Module 5 - Hereditary Reproduction PDF

Module 5 - Hereditary IQ: How does reproduction ensure the continuity of a species?? 5.5.1: Explain the mechanisms of reproduction that ensure the continuity of a species, by analysing sexual and asexual methods of reproduction in a variety of organisms, including but not limited to: - animals...

Module 5 - Hereditary IQ: How does reproduction ensure the continuity of a species?? 5.5.1: Explain the mechanisms of reproduction that ensure the continuity of a species, by analysing sexual and asexual methods of reproduction in a variety of organisms, including but not limited to: - animals: advantages of external and internal fertilisation - plants: asexual and sexual reproduction - fungi: budding, spores - bacteria: binary fission (ACSBL075) - protists: binary fission, budding Reproduction - The process of creating new individuals or offspring from their parent(s). - Allows favourable continuity of a species. - Two types: asexual and sexual reproduction. Asexual Reproduction - https://www.youtube.com/watch?v=i9zj9V8OWRk - The production of identical offspring form just one parent. - Produces new offspring by mitosis. - The offspring are clones as they are genetically identical to the parent unless mutations occur - causing problems due to lack of genetic variation. - Efficient and simple as individuals do not need to find a mate. - Rapid rate of reproduction. - Works well in environments that are ideal and relatively static. - Energy is not wasted in production of gametes. Advantages and Disadvantages of Asexual Reproduction Advantages: - Efficient form of reproduction - Amount of time and energy to produce offspring is minimal - Population sizes can increase rapidly in optimal environments - There is no need to find a sexual partner - Offspring are genetically identical to the parent cell, so they are well suited to a stable environment. Disadvantages: - Rapid population growth can lead to overcrowding and increased competition for resources.  - The lack of genetic variation in a population can cause death of the entire population if conditions change (e.g. disease or a severe drought) because they are not adaptable to adapt. Methods of Asexual Reproduction - Binary fission: splitting of one cell into two, of equal size. - Budding: outgrowths from a parent cell, each smaller than the parent. - Spore formation - Fragmentation - Vegetative propagation in plants - Parthenogenesis Binary Fission - https://www.youtube.com/watch?v=KIpcCyuypzg - Bacteria reproduce through binary fission. - A single parent cell splits into two approximately equal daughter cells which occurs more quickly in prokaryotes due to the lack of organelles and smaller amounts of DNA. - An exponential process because the population doubles after every cycle of division (C= 2n). - Protists also reproduce via binary fission - slightly different due to being eukaryotes (membrane bound nucleus). Spores - Zombie fungus: https://www.youtube.com/watch?v=vijGdWn5-h8 - Spore rain: https://www.youtube.com/watch?v=Mrphn1zOWaE - The formation of structures that are resistant to adverse environmental conditions and can give rise to complete organisms when conditions become favourable - E.g. Fungi  - Unlike a gamete, a spore does not need to fuse with another cell to produce a new individual. - Spores also differ from seeds, as each spore is a single cell and therefore does not contain an embryo or a food supply. - When environmental conditions are favourable, fungi reproduce asexually. They develop large numbers of spore producing units, or sporangia. Budding: E.g. Fungi (yeast) Budding process: - https://www.youtube.com/watch?v=iyWtp_L0Kzc - Parent yeast cell produces a small outgrowth that grows larger and forms a bud. - The nucleus of the parent cell splits off a smaller daughter nucleus, which migrates into the daughter cell. - Bud detaches from the parent by pinching inwards at the base. - The bud is much smaller than the parent but is genetically identical. - Repeated budding forms a chain of connected - but independent cells. Fragmentation - A form of asexual reproduction of multicellular organisms in which an organism breaks into two or more parts, each of which regenerates the missing pieces to form a complete new organism. - E.g. Planaria https://www.youtube.com/watch?v=QXfTs2-AVvA - Planaria is a flatworm that is able to use fragmentation to reproduce asexually Fragmentation vs Regeneration Parthenogenesis(Gk) - Virgin birth - https://www.youtube.com/watch?v=0ISJ2qTAESQ - The development of an egg in the absence of fertilisation is an unusual form of asexual reproduction known as parthenogenesis - Parthenogenesis occurs in many types of invertebrates including scorpions, nematodes, mites, water fleas, wasps, some bees, and other insects. Parthenogenesis may occur in some vertebrate animals as well, such as amphibians, some fish, reptiles, and in a few bird species. - Can occur only in females (development of egg) - The Zebra Shark: https://www.youtube.com/watch?v=KH0KItspmvs Protists Binary fission: - A membrane-bound nucleus that needs to be replicated means that it is a different type of binary fission - The body of an individual is pinched into two parts or halves; the parent cell disappears and is replaced by a pair of daughter nuclei in two new cells, although these need to mature to be recognisable as members of the parental species Budding: - Occurs when a new identical organism grows from the body of the parent  - Usually occurs on the outside of the cell from which it detaches to live independently or sometimes remains in contact to form a colony - As the division of cytoplasm is unequal, the new organism is much smaller than the parent at first. Animals - Regeneration: when a detached part of an individual grows into another individual. - Fission can occur in multicellular animals to produce 2 new offspring e.g. jewel anemone and flatworms. - Budding: producing genetically identical but smaller buds as outgrowths from the parent e.g. hydra and sponges. - Fragmentation: the body of an organism breaks into two or more parts, each of which regenerates the missing pieces to form a new, complete individual. - Parthenogenesis: the development of an egg in the absence of fertilisation. Plants - Vegetative Propagation - The growth of specialised plant tissues that can grow into a new plant if it becomes separated from the parent plant. - Can produce a rapid increase in the number of plants growing in an area so that they can outcompete, or displace, neighbouring species. However, under constant competition from sister and parent plants for resources. - Some plants also undergo asexual reproduction when broken off pieces of branch regenerate into identical new plants - fragmentation. - Occurs when new individuals arise from portions of the root, stem, leaves or buds of adult individuals and are genetically identical to their parents. Include: - rhizomes - runners - tubers - bulb and corn - suckers - budding - fragmentation Vegetative Propagation Examples Runners (modified stems) - Long thin modified stems that grow along the surface of the soil e.g. strawberries can be produced at very alternate nodes on a stem runner. - Advantage- enables reproduction in harsh climates and is rapid Rhizomes (modified stems, underground) - They give rise to a new shoot at each node, farmers often propagate them by splitting the rhizomes e.g. ginger Suckers (modified roots) - roots of some plants give rise to suckers or shoots which give rise to new plants - Trees and shrubs that sucker, such as reeds, wattles and blackberries, can spread quickly into a vacant patch of habitat after disturbance Apomixis - produce offspring from generative tissue without involving fertilisation or the production of seeds - It’s seen in plants such as kangaroo grass, lemon and orange trees and dandelions. Moss Spore Capsule Perennating Organ: Example Summary Sexual Reproduction: Two organisms of the same species get together and combine their genetic material (fusion of gamete: fertilisation) to create a new organism that’s genetically a bit different. Asexual Reproduction: reproduction that doesn’t require mixing genetic material, and allows reproduction whenever, like creating a genetic clone. Vocabulary: - Meiosis - Mitosis - Haploid (n): 23 - Diploid (2n): 46 - Gamete: sperm (male) or ovum (female) - Zygote: fertilised egg Asexual reproduction examples: - Binary fission (e.g. in bacteria and protists) - Reproduction in fungi by budding and spores - Budding (e.g. in corals, hydras and protists) - Fragmentation (e.g. in sea stars and annelid worms) - Vegetative propagation in plants: runners(e.g in strawberries) - Vegetative propagation in plants: bulbs (e.g. in daffodils) - Vegetative propagation in plants: stem tubers (e.g. in potatoes) Protists (Ciliates) - A micronucleus contains a normal diploid set of chromosomes or a macronuclei which contains many sets of chromosomes. - Under stressful environments, they can reproduce sexually through conjugation. - This benefits the species as it introduces genetic variation which helps the population adapt to the changing environment. The Sex Life of Plants Flower Part Function Male, Female, Neither Petal Attracts pollinators with its colour Neither and scent. Protects reproductive organs. Sepal Protect the flower bud before it Neither opens. Stem (pedicel) Supports the flower and transports Neither nutrients and water. Ovary Contains ovules, which develop into Female seeds after fertilisation. Stigma Receives pollen during fertilisation. Female Style A tube that connects the stigma to Female the ovary, allowing pollen to travel down. Anther Produces and releases pollen, which Male contains male gametes. Filament Supports the anther, positioning it Male to release pollen. Pollen Contains male gametes for Male fertilisation. Types of Pollination - Self-pollination: the transfer of the pollen grain from the anther of a flower to the stigma of the same flower in the same plant or to the different plant which is genetically similar. - Cross pollination: the process of applying pollen from one flower to the pistils of another flower. Advantages and Disadvantages of Sexual Reproduction Advantages: - Genetic variation → increased chances of survival (natural selection). Disadvantages: - Slow reproductive rate. - Competition for mates. - Meiosis can also lead to negative traits. - Potential for STD’s. - Costly (making gametes, mating, parenting). Sexual Reproduction - Union of male and female gametes (sperm and egg) to form a unique individual. - Each offspring of two parents has a unique genetic identity while at the same time continuing the species line creates genetic variation. This is due to meiosis. - After fertilisation, two haploid cells fuse to form a zygote → embryo → foetus. - Sexual reproduction involves the fusion of haploid gametes (sperm and ovum) to form a zygote (diploid). - Once the zygote forms, it continues to divide by mitosis. - Requires large amounts of energy, also time consuming to find a mate. Animals - Reproductive strategies involve complex behavioural, physiological and structural adaptations for attracting mates, mating, and protecting and nurturing developing offspring. - Animals may use external or internal fertilisation. External Fertilisation - A male’s sperm fertilises a female's egg outside of the female’s body. - Usually occurs in aquatic animals. - Usually occurs more rapidly due to more gametes being produced and released into the environment. - Parents have no control over the gametes ounces released but also do not need to expend energy on gestation. - Gametes are exposed to predation, disease and natural processes once released. - E.g. spawning by amphibian and bony fish. Sexual Reproduction in Animals: Internal Fertilisation - https://www.youtube.com/watch?v=sz3Yv3On4lE - Key to successful fertilisation: gametes must meet and not dehydrate in the process. - Internal fertilisation is typical of many terrestrial organisms. - The internal environment: protects gametes from dehydration, protects loss to external elements and protects the fertilised eggs and developing young from immediate predation. - Therefore, fewer eggs are required for the survival of a sufficient number of offspring. - The internally fertilised egg may develop a shell and be laid in the external environment (oviparous) to complete its development (in reptiles and birds), or it may continue to develop inside the female’s body. - In most mammals, the fertilised egg becomes an embryo that is nurtured inside the female parent’s body, obtaining nutrients through a placenta, and is born alive (viviparous development). - The gametes of all mammals undergo fertilisation internally. - Mammals are divided into: - Placental: e.g. humans and dogs, completion of embryonic development inside the uterus. - Marsupial: e.g. the red kangaroo, develop internally then continues embryonic development in a pouch. - Monotremes: e.g. platypus and echidna, they are oviparous.  Internal Fertilisation External Fertilisation Advantages - Terrestrial - Fast and prolific - Less gametes - No parenting produced - Wide dispersal of - Higher chance of young success - Female can continue - Gametes and zygotes to reproduce while are protected young develop - Developing young are protected Disadvantage - Slower - More gametes need - Mating can be to be produced complicated - No control over - Potential for STD’s gametes once - Costly released - Parenting is hard - Decreased chance of fertilisation - Must be aquatic Sexual Reproduction in Plants - Ferns. - Vascular system. - Characterised by the absence of flowers and fruit, the production of tiny spores instead of seeds, and by altering generations of free living, spore producing plants and gamete producing plants. Sexual reproduction in plants - Gymnosperms - Vascular, non-flowering seed plants including conifers (cone producing) - The seeds of gymnosperms are produced by cones instead of flowers and when mature they are exposed rather than surrounded by a fruit - Pollinated by wind between the seed cone (female) and pollen cone (male) - An unusual feature of conifer reproduction is that it can take two or more years from the haploid stage of pollination to the diploid stage of fertilisation and the release of the seed. Sexual Reproduction in Plants - Angiosperms (flowering plants) - https://www.youtube.com/watch?v=HLYPm2idSTE - Flowers are the reproductive organs of plants. - A flower can have both female and male parts or only one. - The stamen are the male parts of the flower: - Anther - where pollen (male gametes are found) grains are formed. - Filament - stalk that carries the anther. - The carpel are the female parts of the flower: - Stigma - sticky surface where pollen adheres (sticks). - Style - joins the stigma to the ovary. - Ovary - where ovules are formed. - The process of gamete transfer is called pollination. - In order for fertilisation to occur, the male gametes inside pollen must be carried front he anthers down the style to the ovary. - Once pollen has been deposited on the stigma, a pollen tube germinates and grows down the style, carrying inside it the sperm to an ovule contacted in the ovary. - In flowering plants, fertilisation occurs internally inside the ovary. Parts of a Flower Pollination - Plants depend on wind,water and animals to carry their pollen, from the anthers of one flower to the stigma of a flower either on another plant (cross pollination) or on the same plant (self pollination). - Cross pollination ensures greater variation in the offspring. - After the sperm cell fuses with the egg cell inside the ovule, the fertilised ovule develops, protected within the ovary. - The ovule containing an embryo is now termed a seed and the surrounding ovary grows to become a fruit. Comparison of Pollination Wind pollinated Bird pollinated Insect pollinated Petals Small, inconspicuous, dull Large, colourful Large, colourful Scent Absent Rarely fragrant, birds have High fragrant, insects are little sense of smell attracted to scents Pollen Small grains, light and Sticky or powdery pollen, Large grains, sticky, small powdery, large amounts small amount amount produced Image Fertilisation Successful fertilisation can only occur following acceptance of the pollen grain by the stigma and of the pollen tube by the style. Seed Dispersal - https://www.youtube.com/watch?v=3G1arGl8RvA - After fertilisation, the ovary develops into the fruit and the ovules become seeds. - When the seeds are mature they need to be dispersed away from the parent plant. - It is an advantage for seeds to be dispersed over a wide distance as this helps present overcrowding and competition for light, water and soil nutrients. - Widespread distribution also increases the chances of continuity of the species in other locations, in case there is a sudden change in the local environment, such as fire or disease. Seed Germination - The embryos in seeds lie dormant until the conditions are appropriate. - Water, oxygen, temperature and day length are major environmental factors that influence seed germination. - Many seeds can remain dormant and only germinate when conditions are favourable. - If the seed lands in unsuitable soil that provides sufficient water, oxygen and warmth, it germinates.  - Once the seedling becomes established, it grows and develops into an adult plant that can begin the reproductive cycle once again. Summary of Sexual Reproduction in Plants - https://www.youtube.com/watch?v=eZSowWehZTA - https://drive.google.com/file/d/1eyElc9_5hBd9OyYU9qbenIPFlhitZXQ5/view 1. Pollination- plants depend on agents such as wind, water and animals to carry their pollen from the anthers of one flower to the stigma or the same or another plant. 2. Fertilisation- the sperm cell that was transferred by the pollen tube fuses with the egg cell inside the ovule in the female part of the flower 3. Seed dispersal- seeds (fertilised ovules) are dispersed preferably over a wide distance as it prevents overcrowding and competition for light, water and soil. 4. Germination- the plant embryo inside the seed needs to land on suitable soil that provides sufficient water, oxygen and warmth to germinate Sexual Reproduction in Mammals 5.1.2 Analyse the features of fertilisation, implantation and hormonal control of pregnancy and birth in mammals. Marsupial Mammals The under development of the joey is protected and nourished in the external pouch after an early birth, allowing another fertilisation to occur internally. Examples include kangaroos, brushtail possum, wombats and koalas. Both placental and marsupials are viviparous, that is they give birth to developed, live young. Monotreme Mammals - THere are two monotremes, the platy[us and the echidna - The female lays eggs and each puggle develops inside a leathery eggshell, then hatches to be protected and fed milk by its mother. - Monotremes are oviparous, that is they lay eggs in which their young develop. Placental Mammals A uterus provides nourishment and protection, via a placenta and umbilical cord, for the developing embryo and foetus until birth. After birth these mammals are nourished with milk and develop a covering of fur. Examples include humans, horses, dogs, mice, seals, elephants and whales. Ovulation and Meiosis Males continually produce sperm after puberty. Females on the other hand are born with immature egg cells already in their ovaries. After reaching maturity (puberty), the ovarian cycle commences. Later in life females cease to ovulate; this is called menopause. Before a female is born, meiosis has begun in all oocytes (immature egg cells) but is arrested at an early stage. Once she reaches puberty, pituitary hormones control the continuation and completion of meiosis I. Meiosis II begins, but is paused until fertilisation occurs. Meiosis II only completes after fertilisation. Reproductive Mechanisms in Mammals Mammals have several reproductive mechanisms to maximise reproductive access, including: - Internal fertilisation to increase the likelihood that gametes will meet (this occurs in all three subclasses of mammals) - Implantation of the embryo into the uterine wall, with internal development of the embryo (marsupials and eutherians) to increase the embryo’s chance of survival. - Pregnancy to allow the developing young to be protected from the external environment, have a constant nutrient supply and complete a gestation period (short in marsupials; prolonged in eutherians, whose young are well developed when they are born). Fertilisation - https://www.youtube.com/watch?v=_5OvgQW6FG4 - The fusion of two haploid gametes (egg and sperm) to form a single diploid zygote cell. The zygote cell contains the genetic material of both the egg and the sperm. - There are equal genetic contributions from the male and female parents to the zygote and subsequent offspring. - Sperm cells move in one direction towards the egg. Fertilisation occurs in four steps that are similar for all types of mammals. 1. The sperm use enzymes form the acrosome to dissolve and penetrate the protective layer (zona pellucida) surrounding the egg to reach the cell membrane.  2. Molecules on the sperm bind to receptors (specialised proteins) on the egg’s cell membrane to ensure that a sperm of the same species fertilises the egg, then the nucleus of the sperm enters the cytoplasm in the gg cell. 3. Changes at the surface of the egg occur to prevent the entry of multiple sperm nuclei into the gg. 4. Fusion of the haploid egg and sperm nuclei results in a diploid zygote cell (the fertilised egg). Implantation - The zygote continues to travel down the oviduct until it reaches the uterus. - The first stage of development is cleavage - a period of rapid cell proliferation during white single-cell zygote is divided into many hundred of smaller cells by mitosis. - This mitosis transitions the cell to a morula. This is a ball of unspecialized embryonic stem cells. - The continued mitosis causes the morula to become a blastocyst as its cells begin to differentiate. The inner cell mass will give rise to the embryo and the outer layer of cells will help the placenta develop. - After implantation, gastrulation occurs to form a gastrula which eventually becomes a fetus. - The important part of the process is for the blastocyst to adhere to the lining of the uterus. The outer layers of the blastocyst initiate the formation of the placenta. - The placenta brings the blood vessels of the fetus into close contact with maternal blood through diffusion to exchange nutrients, gases and waste Development of the Embryo - Ectoderm- forms epidermis, hair, brain and spinal cord cells - Mesoderm- forms muscle, cartilage, kidney and gonad cells - Endoderm- forms the lungs, bladder, and lining of the digestive system Hormones - Hormones are chemical substances that act as messengers in the body, coordinating many aspects of functioning, including metabolism and reproduction, so that actions within the body are synchronised. - The pituitary gland secretes hormones that stimulate or inhibit other endocrine glands, regulating the release of their hormones for growth, metabolism and reproduction. Hormones of the Reproductive System - Sex hormones specifically affect the growth and functioning of the reproductive organs or the development of secondary sex characteristics. - The reproductive organs only mature and begin their reproductive function when stimulated by hormones secreted during puberty. - In humans, puberty generally occurs between 10-24 in girls and 12-16 in boys. - There are 3 types of sex hormones: androgens, oestrogens, progestogens. Androgens - https://www.youtube.com/watch?v=-SPRPkLoKp8 - Androgens control the development and functioning of male sex organs and secondary sex characteristics such as deepening of the male voice, increase in the growth and thickness of hair and in the size of muscles and bones. - Cells in the testes secrete the androgen testosterone, which plays a primary role in spermatogenesis (sperm production). - Androgens are present in males and females and their production increases during puberty in both sexes, but it’s higher in males. Sex Hormones - Oestrogens - Oestrogens control the development and functioning of the female reproductive system and secondary sex characteristics such as enlarged breasts, pubic hair and widening of the hips. - Oestrogens are present in both males and females, but occur in much higher levels in females of reproductive age. - Promotes menstrual cycle - Oestradiol is a type of oestrogen hormone. Sex Hormones - Progestogens - https://www.youtube.com/watch?v=Wp4JjMJYLqk - Progesterone is the most common progestogen and it plays a primary role in pregnancy - prepares uterus for, and maintains pregnancy, specifically, it prepares the endometrium for implantation of the fertilised ovum and pregnancy. - It also stimulates the secretion of milk in mammary glands (lactation) and a drop in its levels plays a role in initiating menstruation. Hormonal Control of the Female Reproductive Cycle - Endocrine glands regulate and control the ovarian and menstrual cycles in a coordinated manner, synchronising these cycles to ensure fertility → increases the probability of successful reproduction, biological fitness → continuity of species. - Oestrogen and progesterone regulate the: Ovarian cycle- controls the production and maturation of gametes (ova) Menstrual cycle- prepares uterus for implantation of a fertilised egg Maintenance of pregnancy Preparation for and maintenance of lactation The pituitary gland secretes: - Follicle stimulating hormone (FSH), stimulates maturation of follicles in the ovaries of females, controls when eggs in the ovaries ripen and causes the ovaries to release oestrogen. - Luteinising hormone (LH), promotes final maturation of the ovarian follicle, ovulation and development of the corpus luteum in females. It also stimulates the secretion of testosterone. Controls when eggs are released into the oviduct. - Prolactin in females which acts on breast tissue to prepare for and maintain milk production. Ovarian Cycle - Females are born with all their ova however, they are immature and they mature during puberty. - The ova in the ovaries become surrounded by a single layer of cells that envelop them and begin to divide, resulting in the formation of primary (dormant) follicles in the ovary. - Hormones, during puberty, trigger the development and maturation of ova each month (except during pregnancy), until menopause. Ovarian Cycle - Follicular Phase - Under the influence of FSH, one of the ova will mature within a group of nutritive cells called a follicle. - The follicle cells secrete fluid, which pushes the egg to one side of the follicle. - The enlarged follicle moves to the surface of the ovary and creates a bulge. It is now mature and is called a Graafian follicle. The development from the primary follicle to the Graafian follicle takes approximately 10-14 days. - During this phase, the cells lining the follicle secrete oestradiol (an oestrogen hormone). This causes a surge in the production of LH, which results in ovulation and stimulates the next phase. - The Graafian follicle bursts, releasing the egg, known as ovulation. The funnel-shaped open ends of the uterine tube contain cilia which draw the egg into the tube towards the uterus. - If sperm are present, fertilisation may occur. Ovarian Cycle- Luteinising Phase - Lasts for 14 days and begins after ovulation, when the burst follicle in the ovary enlarges and changes colour, building up a yellow protein called lutein - corpus luteum. - The corpus luteum secretes large amounts of oestrogen and progesterone, which acts on the uterus, preparing it for pregnancy by thickening the lining. Menstrual Cycle - The cycle changes in the ovary (ovarian cycle) is accompanied by a cycle of chances in the uterus (menstrual cycle aka uterine cycle) → occurs in sync. - An average menstrual cycle lasts approximately 28 days. - It starts with menses (menstrual period), which lasts about 4 days. This is where the endometrium (lining of the uterus) breaks down and tears away. This is accompanied by bleeding, which is known as menstruation. - The first day of menses marks the beginning of the follicular phase, which ends on the day of ovulation. - Following menstruation, a new endometrial lining forms in the uterus over about 5-12 days, known as the pre-ovulation phase. - Ovulation takes place in an ovary about 13-15 days after the start of menstruation. - After ovulation, the corpus luteum secretes progesterone and oestrogen into the bloodstream. - Progesterone prepares the endometrium which becomes highly vascularised, reaching a peak 8 or 9 days after ovulation, around the time of expected implantation. - If a fertilised ovum implants in the uterus, pregnancy results and the uterine wall is maintained by the secretion of progesterone and oestrogen. - During pregnancy, a placenta forms, attaching the developing embryo to the uterine wall. - The placenta secretes progesterone, oestrogen and human chorionic gonadotropin (HCG) to maintain pregnancy. Ovarian Cycle and Menstrual Cycle Hormonal Control of the Male Reproductive Cycle - Spermatogenesis (production of sperm) involves the interaction between: Hypothalamus in the brain Pituitary gland at the base of the brain Leydig cells in the testes - Luteinising hormone (LH) stimulates the production of testosterone and Follicle stimulating hormone (FSH) stimulates the production of a protein by Sertoli cells (nurse cells that help develop sperm) in the testes, to maintain testosterone at a level high enough to promote spermatogenesis. Hormonal Control Pregnancy and Labour - The first hormone in pregnancy is hCG (human chorionic gonadotropin) from the placenta to stimulate blood flow to the pelvic area. - Just before birth the levels of oestrogen and progesterone changes - Oxytocin increases to cause uterine contractions. The pressure from the fetus on the pelvis places pressure on the cervix and stimulates further release of oxytocin to begin labour. - Oxytocin maintains contractions under which the placenta is pushed out and the uterus starts shrinking. This also promotes the protective mother instinct and works with prolactin to stimulate lactation. Pregnancy and Birth - The fetus continues to develop over the period of gestation, growing in size, with cells and tissues becoming specialised whilst protected by the amniotic cavity - Pregnancy begins when the zygotes implants in the female’s uterus and ends when the fetus leaves the uterus.  - In humans, it is divided into 3 trimesters. - Monitored using ultrasound technology. True/False Identify each of the following as true or false a. Human females produce new eggs throughout their lifetime. F b. Human males and females both have separate openings for the urethra and reproductive tubes. T c. A gastrula is the stage that implants and forms a placenta. d. A mature egg is much larger than a sperm. T e. Multiple fertilisation of one egg is common. F f. Cleavage uses mitosis to produce many cells from a single zygote. g. The placenta mixes blood of the mother and fetus. h. Ultrasound scans are used for safe monitoring of a fetus. T Jhemain Hormones - GnRH (hypothalamus → pituitary gland): RSH and LH. - HCG (human chorionic gonadotropin) - Testosterone - Oestrogen - Oxytocin Mitosis and Meiosis Inquiry question: 5.2 - How important is it for genetic material to be replicated exactly? model the processes involved in cell replication, including but not limited to: - mitosis and meiosis (ACSBL075) - DNA replication using the Watson and Crick DNA model, including nucleotide composition, pairing and bonding (ACSBL076, ACSBL077) assess the effect of the cell replication processes on the continuity of species (ACSBL084) 5.2.1 - Model the processes involved in cell replication, including but not limited to mitosis and meiosis Why do cells replicate? - Restoring the nucleus-to-cytoplasm ratio - Growth and development- as the new individual continues to grow in size, new cells become specialised for different purposes. More replications follow and the specialised cells become organised into tissues - Maintenance and repair- the production of identical new cells to replace those that are damaged or die as a result of normal functioning or injury - In unicellular organisms, cells replicate for reproductive purposes Levels of Organisation Vocabulary: - Mitosis: mitosis is a part of the cell cycle in which replicated chromosomes are separated into two new daughter cells. The daughter cells have the exact same genetic materials as the parent cell. - Homologous pair: a pair of chromosomes that match in size. - One is inherited from the mother and one from the father - Diploid: describes a cell with a full set of chromosomes. Contains two of each type of chromosome.  - Haploid: describes a cell with half a set of chromosomes. Contains one of each homologous pair. - Daughter cell: cells that are formed after cell division from the parent cell. The Cell Cycle Cell cycle is the life cycle of a cell, involving growth, replication of DNA (deoxyribonucleic acid) and division to produce two identical daughter cells.The cell cycle has three main phases: - Interphase - Mitosis - Cytokinesis. These phases always occur in this order. Mitosis is only one part of this cycle and usually takes about an hour or two. A complete cell cycle in actively dividing cells may take about 18–22 hours. The cell spends a large amount of time preparing for division (a stage called interphase, which precedes mitosis). The cell cycle is the period between one cytokinesis and the next. The time for a cell cycle is called generation time (T) and varies considerably between different cell types. Mitosis - https://www.youtube.com/watch?v=f-ldPgEfAHI Most animals and plants start off life as just a single cell, but grow to become adults containing billions and billions of cells. How does one cell become billions and billions of cells? The type of cell division that makes animals and plants grow is called mitosis. In mitosis, a parent cell divides into two identical daughter cells. These daughter cells divide in two, and so on. Mitosis is also the way in which old and damaged cells are replaced. The two daughter cells produced by mitosis are genetically identical to the parent cell. What does this mean? All the genes and chromosomes from the parent cell must be copied and passed on to the daughter cells. Normally, a cell only contains one copy of each chromosome, but before dividing a cell must duplicate all its chromosomes. This means that all the genes will also be duplicated. Duplicating Chromosomes A cell’s chromosomes are usually long, thin strands. Just before the cell divides, however, the chromosomes become shorter, thicker and more visible. They are said to condense. Duplicating Chromosomes Each chromosome duplicates and becomes two strands, each one called a chromatid. The two chromatids are joined at the centromere. Chromosome: all genetic material (DNA) compacted together. Chromatid: one copy of a newly copied chromosome which is still joined to the original chromosome. Centromere: a region on the chromosome where sister chromatids are attached. Homologous Pairs: - A pair of chromosomes that match in size. - The same structural features (e.g. same size, same banding patterns, same centromere positions). - The same genes at the same loci positions (while the genes are the same, alleles may be different). Interphase: a period of cell growth and development. - DNA replication (copying) occurs during interphase. So 46 chromosomes gets duplicated to become 92 total chromosomes (23 sets become 46 sets). - During interphase the cell also grows, carries out normal cell activities, replicates all other organelles. - The cell spends most of its life cycle in interphase. Prophase - Chromosomes coil up. - Nuclear envelope disappears. - Spindle fibres. Metaphase (Middle) - Chromosomes line up in the middle of the cell.  - Spindle fibres connect to chromosomes. Anaphase (Apart) - Chromosome copies divide. - Spindle fibres pull chromosomes to opposite poles. Telophase (Two) - Chromosomes uncoil. - Nuclear envelopes form. - 2 new nuclei are formed. - Spindle fibres disappear. Cytokinesis: the division of the rest of the cell (cytoplasm and organelles) after the nucleus divides. - In animal cells the cytoplasm pinches in and in plant cells the cell plate forms. - After mitosis and cytokinesis, the cell returns to interphase to continue to grow and perform regular cell activities. Interactive Mitosis Meiosis 1. Meiosis is the type of cell division that occurs in the sexual reproductive organs of a plant or animal( eukaryotes), and results in the formation of gametes (sex cells) 2. It produces four daughter cells (gametes) that are genetically unique. 3. Meiosis ensures that the chromosome number of each species is maintained (not doubled) during sexual reproduction 4. Meiosis is called a reduction division because, unlike mitosis, it reduces the number of chromosomes in gametes (daughter cells) to half (ln or n) of that in somatic cells (2n). Meiosis: Stages Unlike mitosis, there are two sequential rounds of division in meiosis, called meiosis I and meiosis Il each ,with these sub-phases. Meiosis: Crossing Over and Recombination - Chromatids of homologous chromosomes may exchange portions of their genetic information - The point where crossing over occurs is called a chiasma. - Significance- produces chromosomes with new combinations of genetic information - The random assortment of maternal and paternal chromosomes and their alleles in gametes is also responsible for genetic variation. Comparison Mitosis and Meiosis DNA Replication and Structure The letters ‘DNA’ are shorthand for Deoxyribo(se) Nucleic Acid. The structure of DNA - The DNA molecule actually looks like a spiral staircase, or a ladder that twists. - This spiral is called a double helix - The spiral is right handed, that is, it spirals in a clockwise direction - DNA is a very long and thin molecule that makes up part of a chromosome How many molecules of DNA does a human have? Each molecule of DNA winds itself up like a piece of string around proteins forming an elongated ball. Each ‘ball’ in this case is known as a chromosome. Humans have 46 chromosomes – 23 from each parent - in each of the trillions of cells that make up their body. The egg and sperm have 23 chromosomes. - Chimps have 48 (2N) chromosomes - Dogs have 78 (2N) chromosomes - Horses have 64 (2N) chromosomes - Fruit flies have 4 (2N) chromosomes - Peas have 14 (2N) chromosomes What is the helix of DNA composed of? The long thin helical molecule of DNA is made up of bases represented by the letters A (adenine), T (thymine), G (guanine) & C (cytosine). DNA is also made up of sugar and phosphate molecules. One base, one sugar and one phosphate make up a nucleotide. - The bases are what actually make up the genetic code, they are like the blueprint that gives us our appearance. Two bases join together to form what would be the ‘rung’ of the DNA ‘ladder’. - The ‘uprights’ of the DNA ‘ladder’ are made of alternating sugar and phosphate molecules. They are known as the backbone of the DNA molecule that runs down the outside. Structure of a nucleotide A nucleotide is made of 3 components: 1. A Pentose sugar - This is a 5 carbon sugar - The sugar in DNA is deoxyribose. - The sugar in RNA is ribose. 2. A Phosphate group - Phosphate groups are important because they link the sugar on one nucleotide onto the phosphate of the next nucleotide to make a polynucleotide. 3. A Nitrogenous base In DNA the four bases are: - Thymine - Adenine  - Cytosine - Guanine In RNA the four bases are: - Uracil - Adenine - Cytosine - Guanine Nitrogenous bases - Two types - Pyrimidines: Thymine (T), Cytosine (C), Uracil (U) - Purines: Adeine (A), Guaine (G). Sugar phosphate bonds (backbone of DNA) - Nucleotides are connected to each other by covalent bonds between the phosphate on one nucleotide and the sugar on the next nucleotide - Occur between the –OH group on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon of the next. - This means the free ends of the DNA molecule are different to each other (one phosphate 5’ and other OH on 3’. The strands are said to be ‘antiparallel’ to each other. The Structure of DNA - The sugar and phosphate make the outer backbone of the DNA molecule as they link the nucleic acids - This is only half the story showing one side of the ladder or one side of the helix - To make a double helix the bases form hydrogen bonds with other bases - To make the double helix, the A and T must always bond, and the G and C must always bond - This is because there is exactly enough room for one purine and one pyramide base between the two polynucleotide strands of DNA. - A&T form 2 H-bonds and C&G form 3 H-bonds. - Remember this is only a small section of a molecule of DNA that would really have hundreds of thousands of nucleotides.  - When scientists draw DNA they simplify it. There is no need to draw out the sugar and phosphate back bone every time because we know it is always there. Instead, scientists are generally only interested in the sequence of base pairs. Sometimes they don’t even show the helix or the hydrogen bonds. - https://www.youtube.com/watch?v=o_-6JXLYS-k DNA to Chromosome Can we see DNA Down the microscope? - The bases, sugar and phosphate molecules are too small to see under the microscope on their own. In order to store itself in the nucleus, the DNA molecule folds and folds and folds upon itself so that we can eventually see it as a chromosome. Imagine a piece of string that wraps around itself to eventually form a thick ball that we can see - The reason DNA has to fold so much is because it is so long. A single human cell contains about 1.5 metres of DNA (about 100,000 times longer than the cell itself). The DNA therefore has to package itself up and the chromosome is that package Discovering the structure of DNA - The structure of DNA was identified in 1953 by James Watson and Francis Crick at Oxford University in England using x-ray data collected by Maurice Wilkins and Rosalind Franklin. Watson, Crick and Wilkins shared the Nobel Prize for their work. Franklin died of cancer in her early thirties, which was possibly caused by the radiation she was exposed to when carrying out her research. - X-ray diffraction photograph of the DNA double helix Nature of the Genetic Material - Property 1 - it must contain, in a stable form, information encoding the organism’s structure, function, development and reproduction. - Property 2 - it must replicate accurately so daughter cells have the same genetic makeup. - Property 3 - it must be capable of some variation (mutation) to permit evolution. The Role of DNA - https://www.youtube.com/watch?v=8kK2zwjRV0M - In 1944 Oswald Avery demonstrated that DNA provided the genetic code that carried information from one generation to the next. These genes define our appearance. It undergoes two important procedures to be able to do this.  - Firstly, DNA must be able to make copies of itself so that it can pass on the replicated information to other cells – this is known as replication - Also, DNA must be able to transfer its coded information into a form that can be used by the organism it resides in. It does this by making a polypeptide (which becomes a protein) – this occurs by two processes known as transcription and translation. Replication of DNA - https://www.biointeractive.org/classroom-resources/dna-replication-basic-detail - https://www.youtube.com/watch?v=TNKWgcFPHqw - https://www.youtube.com/watch?v=Qqe4thU-os8 - The DNA molecule unwinds. The hydrogen bonds are then cut by restriction enzymes. DNA polymerase then adds nucleotides from the cytoplasm to the corresponding free bases. Enzymes Involved in DNA Replication Inquiry question - How important is it for genetic material to be replicated exactly? 5.3.1 - Why is polypeptide synthesis important?​ - Construct appropriate representations to model and compare the forms in which DNA exists in eukaryotes and prokaryotes - Model the process of polypeptide synthesis, including: - transcription and translation - assessing the importance of mRNA and tRNA in transcription and translation - analysing the function and importance of polypeptide synthesis - assessing how genes and environment affect phenotypic expression - Investigate the structure and function of proteins in living things Prokaryotic DNA - Simple cells e.g. bacteria - Contain single chromosomes in the form of a circular strand of DNA - It floats in a dense region called the nucleoid - It is not a helix, rather two circles of single stranded DNA twisted around each other. - Non chromosomal DNA called plasmids which aren’t essential for the survival of the bacteria but do provide selective advantages e.g. antibiotic resistance - Approximately 1300μm (1.3mm) - Genome is compact- no introns Eukaryotic DNA - Enclosed within a membrane-bound nucleus in the cell. - Consists of multiple separate chromosomes. - Human cells contain approximately 2 metres of DNA, organised into 46 chromosomes. - The number of chromosomes in eukaryotes doesn't necessarily indicate the complexity of the organism. - The Chinese giant salamander has 60 chromosomes but is less complex than humans. - Eukaryotic cells often have a significant amount of non-coding DNA, known as introns.  - In humans, only 3% of DNA is coding DNA (exons), which contains sequences for making products like proteins or RNA. - Non-coding DNA may play a role in gene spatial organisation and gene expression control. - There are two theories regarding introns: they may have accumulated during eukaryotic evolution, or they were lost from prokaryotes as they evolved to simplify their genomes for rapid division. Non-nuclear DNA in eukaryotes - Located in Chloroplasts and mitochondria. - Inherited independently of nuclear DNA - mtDNA is used to study evolutionary relatedness, construct evolutionary trees, investigate family relatedness and identify people in forensic science. RNA - Important role in polypeptide synthesis to produce functional proteins​ - Ribonucleic acid ​ - RNA only exists as a single strand​ - RNA polynucleotide strands are much shorter than DNA​ - Ribose sugar in the backbone​ - Nitrogenous bases are G, C, A and U (replaces T)​ - Three main forms: messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA)​ Forms and storage of DNA Prokaryotes - Double-stranded, circular DNA chromosomes​ - Contained in the nucleoid region​without a membrane. - No telomeres due to being joined in a circle​ - Plasmids- double stranded DNA which replicates independent of chromosomal replication​ - No histone proteins to condense DNA due to much less genetic material​ Genome Size: Typically smaller. Genetic Variation: Prokaryotes rely on horizontal gene transfer and mutations for genetic diversity. Eukaryotes - Chromosomes contain a single DNA molecule and associated histone proteins​ - Linear chromosomes with a constant number in each species​  - Histones allow the DNA to wind up- average length of DNA in a single chromosome is 4.76cm long​ - The chromosomes must condense when preparing to divide​ Genome size: Larger and more complex Genetic variation: Mechanisms like sexual reproduction and genetic recombination. Polypeptide Synthesis Inquiry Question: Why is polypeptide synthesis important? Model the process of polypeptide synthesis, including: - transcription and translation - assessing the importance of mRNA and tRNA in transcription and translation - analysing the function and importance of polypeptide synthesis Key Terms: - Gene: a section of the DNA is being transcribed into mRNA - mRNA: a mobile copy (transcript) of the DNA segment (gene). It is translated at the ribosome - Ribosome: this facilitates the translation of mRNA into a polypeptide - tRNA: brings amino acids to the ribosome. - Nucleus: where DNA is stored, and transcription occurs - Cytoplasm: where translation occurs Role of Proteins - Enzymes - Help to speed up reactions in living cells by binding to active sites - Antibodies - Antibodies are proteins that are produced by the immune system to fight infection and remove foreign viruses or bacteria. Substances that trigger the release of antibodies are called antigens  - Structural Proteins - Structural proteins provide support for our bodies and cells. The most prominent structural proteins are the keratins, which form skin, fur, hair, wool, claws, nails, hooves, horns, scales, beaks and feathers. - Transport Proteins - The last type of protein we are going to look at are transport proteins. These proteins move molecules around our bodies. E.g haemoglobin - The order of the nucleotides in DNA determines which polypeptides are synthesised. - Groups of three nucleotides are called triplets - When a DNA triplet is transcribed into mature mRNA, the triplet is then called a codon Role of RNA - mRNA- messenger RNA- carries a complementary copy of the nucleotide sequence of DNA that specifies the amino acid sequence for a particular polypeptide - rRNA- ribosomal RNA- together with proteins, rRNA forms a ribosome which is where the information in the mRNA is translated into a chain of amino acids - tRNA- transfer RNA- transfers amino acids from the cytoplasm to the ribosomes, where they are joined to form a polypeptide chain based on the sequence of Gene Expression The process by which the information stored in a gene synthesises a functional gene product In eukaryotic cells this occurs in three stages: - Transcription- occurs within the nucleus - RNA processing- occurs within the nucleus - Translation - occurs in cytoplasm on ribosomes Exons- regions of a gene that are usually ‘expressed’ as proteins or RNA Introns- non-coding regions of a gene that are spliced out of the mRNA during processing Transpiration - Process of producing single-stranded mRNA from DNA - Occurs in the nucleus - The strand of DNA being transcribed is the template strand (non-coding) RNA Processing - Forms mature mRNA from pre-mRNA, after removing non-coding sequences (introns) so that only coding sequences (exons) are carried to the ribosome for translation - Only in eukaryotes as prokaryotes do not carry introns - Also includes: - The addition of a 5’ cap. - The addition of a poly(A) tail, both of which make the mRNA more stable and prevent degrading) - Splicing (removal of introns) Translation - Process in which the codons on mRNA are translated into a sequence of amino acids resulting in a polypeptide - Occurs on ribosomes - Ribosomes act as docking stations for the tRNA to deposit their specific amino acids for the mRNA molecule Modelling Polypeptide Synthesis - Try not to dump large amounts of information onto your model- your report is for information. - Don’t spend a ridiculous amount of money- you can even use coloured paper, paddle pop sticks, pipe cleaners, the arts and craft section of kmart would be a good place to visit - PLAN your model! Use an A4 piece of paper to pencil in what your model will look like - Presentation is key, a model is informative but also looks good! Make it neat, well presented and aesthetically pleasing. Protein Synthesis Prokaryotic protein synthesis Eukaryotic protein synthesis 30S and 50S ribosomal subunits 40S and 60S ribosomal units Each mRNA may contain the coding Each mRNA contains the coding sequence for sequences of several genes one gene Overlap between transcription and No overlap. Transcription and processing in translation- coupled. Due to DNA and the nucleus. Translation and protein synthesis ribosomes being in the cytosol together in the cytoplasm No processing Have introns and exons so splicing is required No 5’ cap or poly (A) tail is added to mRNA 5’ cap and poly (A) tail is added to mRNA Function and Importance - Highly regulated mechanisms are required to determine that the correct polypeptides and proteins are produced when and where they are required - Amino acids- linked by a chemical bond (peptide bond) and form polypeptides - Polypeptide- many peptide bonds- a non-functioning component - Protein- fully functioning molecule Key Points - Each DNA triplet or codon codes for one amino acid may also provide specific instructions, such as ‘start translation’ and ‘stop translation’ - The genetic code for determining amino acid sequences works in sets of three bases (nucleotides): on DNA, the set of three is called a triplet; on mRNA, it is called a codon; on tRNA, it is an anticodon. For example, the coding for lysine if: DNA triplet TTC, mRNA codon AAG, tRNA anticodon UUC (remembering that RNA has U instead of T). Genetic Variation Inquiry Question 4: How can the genetic similarities and differences within and between species be compared? conduct practical investigations to predict variations in the genotype of offspring by modelling meiosis, including the crossing over of homologous chromosomes, fertilisation and mutations (ACSBL084) model the formation of new combinations of genotypes produced during meiosis, including but not limited to: – interpreting examples of autosomal, sex-linkage, codominance, incomplete dominance and multiple alleles (ACSBL085) – constructing and interpreting information and data from pedigrees and Punnett squares collect, record and present data to represent frequencies of characteristics in a population, in order to identify trends, patterns, relationships and limitations in data, for example: – examining frequency data – analysing single nucleotide polymorphism (SNP) Meiosis - Meiosis is an important cell division process that is required for sexual reproduction and creating genetic Variation. - It produces four daughter cells (gametes) that are genetically unique. - Meiosis occurs only in eukaryotes and only to form the gametes Genetic Variation and Meiosis Crossing Over and Variation - Crossing over (synapsis) ensures that not all linked genes on a chromosome are inherited together. - The exchange of genes during crossing over causes mixing of paternal and maternal genes and introduces genetic variation. - Each pair of chromosomes then separate (anaphase I) and one entire chromosome moves into a daughter cell. This separation of maternal and paternal chromosomes leads to genetic variation depending on which chromosome of each pair ends up in which daughter cell, also known as independent assortment. Variation - Independent Assortment - Meiosis randomly separates homologous chromosomes. - During metaphase I, sister chromatids can line up neatly or randomly. - This causes different combinations to be pulled to either ends of the cell. - This means that the daughter gametes will have a different proportion of - genes from mum and dad. Variation - Random Segregation - According to Mendel, hereditary units or ‘factors’ (now called genes) must have different forms (now called alleles) that separate randomly during the production of gametes. - These forms would then unite after fertilisation, with each parent contributing one allele to the offspring. - Mendel’s hypothesis became known as the Law of Segregation, or Mendel’s first law. Variation - Mutations - Mutations may arise at any point in the process but most commonly occur during replication of DNA prior to the start of cell division. - There are different types of mutations e.g point mutations & chromosomal mutations (Module 6). - Mutations can delete, add or replace letters or entire sections of genetic code. - These mutations will be replicated and can code for beneficial, harmful or ineffectual traits. - Mutations occur randomly and can create variation within genetic code. - https://www.youtube.com/watch?v=DlhpvcgK_28 parent) fail to separate and move to opposite poles of the cell. As a result, oneVariation - Error in Cell division - Nondisjunction Nondisjunction is an error in cell division that results in the improper separation of chromosomes. This leads to daughter cells with an abnormal number of chromosomes, a condition known as aneuploidy. Nondisjunction in Meiosis Nondisjunction can occur during either Meiosis I or Meiosis II: 2. Nondisjunction in Meiosis I: Occurs during anaphase I of meiosis.  Homologous chromosomes (the pairs of chromosomes, one from each daughter cell receives both members of the homologous pair, while the other daughter cell receives none. Outcome: This results in two gametes with an extra chromosome (n+1) and two gametes with one less chromosome (n-1). 3. Nondisjunction in Meiosis II: Occurs during anaphase II of meiosis. Sister chromatids (the duplicated copies of a single chromosome) fail to separate and move to opposite poles of the cell. One daughter cell receives both sister chromatids, while the other receives none. Outcome: This results in two normal gametes (n), one gamete with an extra chromosome (n+1), and one gamete with one less chromosome (n-1). Variation - Fertilisation - Variation is achieved through fertilisation because gametes are haploid (half genetic info). - This means that half of the DNA comes from the mum and half from the dad. - Providing that the mother and father are not related… the offspring will be genetically different to its parents! Inheritance - Terms you MUST know Autosome Chromosomes that are not involved in sex determination. Humans have 22 pairs of Autosomes.  Allosome Sex chromosomes that carry genes that determine determine the sexual characteristics of a person and therefore determine whether they are biologically male or female. Human have 1 pair of allosomes. Genotype The set of alleles present in the DNA (deoxyribonucleic acid) of an individual organism. It is the result of inheritance. Phenotype All of an organism's observable characteristics.It is the result of inheritance and the effects of the organism’s environment. Allele An allele is an alternative form of a gene. Each individual usually only has two alleles for each trait: one inherited from their mother and one inherited from their father. But one gene may have many alleles, and this is what leads to variation in a population. Homozygous When both alleles are same in an organism, eg. TT or tt, the organism is homozygous for that trait. Heterozygous When the alleles are different, eg. Tt, then the organism is heterozygous for that trait. Allele - Alternative forms of the same gene - An individual can only have two alleles - one from mother, one from father - There can be more than two alleles in the population Inheritance - Overview - Genotype: allele combination for a trait, homozygous or heterozygous - ( e.g: RR, Rr, rr) - - Phenotype: observable characteristics determined by genotype and environment (Red, White) Types of Inheritance Mendelian: - Autosomal (also called complete dominance) Non-mendelian: - Codominance - Incomplete dominance - Sex-linkage - Multiple alleles Genotypic and Phenotypic Ratios - Genotypic and phenotypic ratios are used to express the expected frequency of genotypes and phenotypes in the offspring from a genetic cross. - Punnett squares are used to calculate the expected outcomes of a cross and the possible genotypes and phenotypes generated in the offspring. - The ratio of genotypes in the offspring is written in the following order: - homozygous dominant : heterozygous : homozygous recessive. - The ratio of phenotypes observed in the offspring is written as: - Dominant phenotype : recessive phenotype. The term ‘filial’ refers to the offspring of a cross. The symbols for filial generations are sometimes written in the form F1 (first filial generation), F2 (second filial generation), etc. - It is not always possible to tell the genotype of an organism from its phenotype. - Test crosses are carried out between an organism that exhibits a dominant trait and an organism that exhibits a recessive trait, to determine whether the dominant organism is homozygous or heterozygous for the dominant trait. Punnett Squares - Table that can be used to predict the possible offspring genotype and phenotype outcomes for two individuals (parents) - Allow you to predict the probability of offspring inheriting a condition - The genotype of one parent is written along the top, the other parent along the side - The different possible combinations of alleles in their offspring are determined by filling in the cells of the Punnett square with the correct letters (alleles)  - You match the first allele of the top parent with the first allele of the second parent and so on. - You can then calculate the probability of a particular genotype and phenotype arising from the results. Determining probability of a genotype/phenotype from a Punnett Square - Parent 1 - Tt genotype (top row) - Parent 2 - tt genotype (left column) - 2/4 offspring are Tt genotype - 2/4 offspring are tt genotype - The Punnett square shows the following: - 50% probability of being Tt genotype - 50% chance of being tt genotype - Another way of writing this is that the offspring have a ratio of 1 Tt: 1 tt The phenotype can be written as a ratio as well - 2 brown eyes: 2 blue eyes Autosomal Inheritance/ Complete Dominance - The phenotype of the heterozygotes cannot be distinguished from homozygous dominants. - The presence of a dominant allele will always mask the presence of a recessive allele. - Alleles for a gene can be the same- both recessive or dominant - homozygous e.g. HH, hh - Alleles for a gene can be different- one recessive and one dominant - heterozygous e.g. Hh. Incomplete Dominance - The phenotype of heterozygotes appears as a blend of the phenotypes of either type of homozygote. - Special notation is used to represent the alleles that do not show complete dominance. - A letter is chosen to represent the gene – for example, C for colour. The alleles are written as superscripts next to the gene, so the allele for red would be CR and the allele for white would be Cr Codominance - The phenotype of heterozygotes involves both alleles being expressed, with neither dominant over the other. - Occurs when both alleles are expressed, creating a new phenotype. - Neither allele is dominant or recessive. - Special notation used. - Both alleles are written as capital letters. - As neither allele is dominant or recessive, you use a different letter for each allele - E.g. pure-breeding cattle may have white or red coat colour. Red coat = RR, white = WW. A roan cow would be represented as RW.  - https://www.youtube.com/watch?v=YJHGfbW55l0 Karyotype Self Determination In humans, genes on the X and Y chromosome code for the production of sexual reproductive organs and the development of secondary sexual characteristics that define whether an individual is phenotypically male or female Sex Determination and Sex Linkage During meiosis, both autosomes (body cells) and sex chromosomes segregate. ○ A female has 44 autosomes + XX so when halved, it’s 22 + X. ○ A male has 44 Autosomes + XY, so when halved, it’s 22 + X or Y. A zygote can inherit an XX and will be biologically female or an XY and will be male. Sex-linkage refers to genes that are located on the sex chromosomes Most sex-linked conditions are X-linked (linked to the X chromosome) ○ This is because the Y chromosome is shorter and has less genes on it. Most X-linked dominant traits are more common in females. ○ This is because either allele may be dominant for a trait. X-linked recessive traits are more common in males. ○ This is because females can be a carrier without having the condition. ○ Males only have one X chromosome so only need one copy of the allele to have the condition. What is a carrier? - A carrier is a female that possesses a recessive allele for a condition/trait but does not display that condition herself. - The recessive allele she carries is masked by a dominant allele (one allele on each X chromosome) - A carrier female can still pass down the recessive allele for a trait. X-Linked Recessive Conditions - Males will always inherit an X-linked recessive condition from their mother. - Females will only inherit an X-linked recessive condition if they receive a recessive allele from both parents - Examples of X-linked recessive conditions are haemophilia, colour blindness (red-green) X linked disorder - Haemophilia Haemophilia (a bleeding disorder) is an X-linked disorder. Alleles for this gene occur on the X chromosome. A male who inherits one copy of the mutant allele (on the X chromosome from his mother) will suffer from the condition. Because the male has no equivalent allele on the Y chromosome to mask this defective allele, a single copy of this recessive gene results in the male being affected by the recessive gene. Females have two X chromosomes, one from each parent. Therefore if a female inherits a mutant allele for haemophilia on one X chromosome, she will not suffer from the disorder if her other allele is dominant. Such a female is termed a carrier – the defective allele does not affect her, but may be passed to her sons (who would be affected) or to her daughters (who may be carriers or affected, depending on the allele they inherit from their father). If a daughter inherits a pair of defective alleles for haemophilia (one from each parent, on each X chromosome), the condition is lethal. Sex Linked Inheritance The results of this sex-linked genetic cross can be analysed as follows: - Ratio of 1:1 males to females - Phenotypic ratio of 1 normal male: 1 affected male - 50% chance that any offspring will be affected by the disease. - 25% chance that a boy is affected. Note - Some sources (e.g. the textbook, Blitzing, Khan Academy, ) are not consistent in the way the notation used to write genotypes. - For example, the textbook uses “CRCW” to represent a roan cow. - Technically both are correct - use whichever one is easier for you. - HSC markers will take this into account when marking. - They will specify in the exam stimulus material for the question. - Remember to pay attention to the TYPE OF INHERITANCE in the question when working out the “phenotype” for the offspring based off the Punnett Square! - For example, if the question is about codominance, remember that BOTH ALLELES ARE EXPRESSED and in incomplete dominance there is A BLEND OF BOTH Multiple Alleles - Although individual humans can only have two alleles for a given gene, multiple alleles may exist in a population level - Different individuals in the population may have different pairs or combinations of these alleles. - Multiple alleles makes for many possible dominance relationships (one allele might be dominant over several other alleles, or maybe just dominant over one). - Special notation used to represent the alleles. - A letter is chosen to represent the gene, e.g. C for colour. - The alleles are written as superscripts next to the gene. - May have capital letters, lowercase letters, different superscript letters etc. to represent alleles - E.g. coat colour in rabbits. Four alleles: normal, chinchilla, himalayan, albino. Multiple Alleles - Blood Types - Within a population, there may be three or more alleles for a single gene trait.  - Blood cells have molecular markers on their surfaces and these play an important role in allowing a person’s own body cells to be recognised by the immune system as ‘self’ - Don’t get this confused with ‘polygenic’ traits which is when there are two or more genes coding for the same trait e.g. human height. Pedigrees - Chart that shows the presence or absence of a trait within a family across generations. - Pedigrees are used to analyze the pattern of inheritance of a particular trait throughout a family. Pedigrees show the presence or absence of a trait as it relates to the relationship among parents, offspring, and siblings. Reading a pedigree Pedigrees represent family members and relationships using standardized Symbols. By analyzing a pedigree, we can determine genotypes, identify phenotypes, and predict how a trait will be passed on in the future. The information from a pedigree makes it possible to determine how certain alleles are inherited: whether they are dominant, recessive, autosomal, or sex-linked. To start reading a pedigree: 1. Determine whether the trait is dominant or recessive. If the trait is dominant, one of the parents must have the trait. Dominant traits will not skip a generation. If the trait is recessive, neither parent is required to have the trait since they can be heterozygous. 2. Determine if the chart shows an autosomal or sex-linked (usually X-linked) trait. For example, in X-linked recessive traits, males are much more commonly affected than females. In autosomal traits, both males and females are equally likely to be affected (usually in equal proportions). Example: Autosomal Dominant Trait - This pedigree is showing the inheritance of freckles across three generations. - The diagram shows the inheritance of freckles in a family. The allele for freckles(F) is dominant to the allele for no freckles(f). - At the top of the pedigree is a grandmother (individual I-2) who has freckles. Two of her three children have the trait (individuals II-3 and II-5) and three of her grandchildren have the trait (individuals III-3, III-4, and III-5). Example: X-LInked Recessive Trait Pedigree showing the inheritance of color blindness across four generations. The diagram shows the inheritance of color blindness in a family. Colorblindness is a recessive and X-linked trait (X b ). The allele for normal vision is dominant and is represented by X B. In generation I, neither parent has the trait, but one of their children (II-3) is colorblind. Because there are unaffected parents that have affected offspring, it can be assumed that the trait is recessive. In addition, the trait appears to affect males more than females (in this case, exclusively males are affected), suggesting that the trait may be X-linked. Single nucleotide polymorphisms ( SNP’s pronounced as snips) - A single nucleotide polymorphism is a change of a single nucleotide at a specific position on the genome. This may be a substitution (eg changing A for G), insertion (adding a new nucleotide), or deletion (removing a nucleotide) - Single Nucleotide Polymorphisms (SNPs) pronounced ‘snips’, are another way of examining genetic variation. - SNPs usually arise during DNA replication, where a single nucleotide is incorrectly inserted, creating an error in the DNA sequence at a particular location on a chromosome. - To be a SNP, it must occur in 1% of the population. - There are approximately 10 million known SNPs in the human genome (3 billion base pairs) - In non-coding regions (introns) a SNP does not lead to observable differences, however, are important as they can be used to identify disease susceptibility in individuals. - In coding regions (exons), they can be the cause of a phenotypic change such as appearance or enzyme functioning. - Snips are linked to be associated with human diseases such as Asthma, Osteoporosis, diabetes and Alzheimers. SNP (single nucleotide polymorphism) databases are databases that contain information about genetic variation, which researchers can use to investigate a range of genetic conditions. SNP databases are now so large that special software programs have been developed to help analyse the data and make sense of it. Limitations of SNP’s - SNPs represent only single base changes in the DNA sequence, which means they may not capture larger structural variations such as insertions, deletions, or duplications that can contribute to genetic diversity. - Not all SNPs are equally informative. Some SNPs may be located in non-coding regions or may have no functional impact on phenotypes, making them less useful for understanding traits or disease susceptibility. - Genetic variation is not solely determined by SNPs; environmental factors can also play a significant role in phenotypic expression. This means that SNP analysis alone may not provide a complete understanding of genetic variation. - SNPs that are common in one population may be rare or absent in another, limiting the ability to generalise findings across different populations.