Unit 4 Genetics Bio Test Review Notes PDF

Unit 4 Biology Review Notes Genetics DNA: Deoxyribonucleic acid Located in the nucleus in eukaryotes Contains the genetic information Is double stranded and twisted into a double helix Gene A short section of DNA that is used to produce...

Unit 4 Biology Review Notes Genetics DNA: Deoxyribonucleic acid Located in the nucleus in eukaryotes Contains the genetic information Is double stranded and twisted into a double helix Gene A short section of DNA that is used to produce a proteins Gives organisms traits Chromosomes Structures that organize the genetic material ○ Made of DNA and protein One unbroken DNA molecule forms each chromosome Humans have 46 chromosomes (23 pairs) 22 pairs are autosomes and 1 pair are sex chromosomes (e.g. X and Y) ○ Females are XX and males are XY Haploid vs Diploid Haploid (n): A cell is haploid if it contains one complete set of chromosomes, represented by "n." In humans, haploid cells have 23 chromosomes, one from each pair, which is the chromosome number in gametes (sperm and egg cells). Haploid cells are formed through meiosis, which reduces the chromosome number by half. Diploid (2n): A cell is diploid if it contains two complete sets of chromosomes, represented by "2n." In humans, diploid cells have 46 chromosomes, organized into 23 pairs, with one chromosome of each pair inherited from each parent. Diploid cells are the standard form in most body cells (somatic cells) and are formed through mitosis Why do multicellular organisms do cell division? To grow and replace damaged cells Meiosis The process that forms gametes (sex cells) Involves two stages of cell division and results in cells with half the number of chromosomes Human body (somatic) cell = 46 chromosomes (diploid = 2n) Human gamete = 23 (haploid = n) Somatic cell chromosomes are arranged into 23 homologous pairs ○ Chromosomes in each pair are similar in size, shape, and gene arrangement ○ Each parent gives one member of each pair -> Sperm cell (n=23) + ovum (n=23) = zygote (2n = 46) Stages of Meiosis Meiosis 1 Prophase 1 Nuclear membrane dissolves Chromosomes condense Homologous chromosomes come together (synapse) to form a tetrad Crossing over occurs ○ Homologous chromosomes exchange segments which increases genetic variation Metaphase 1 Chromosome pairs line up side by side at the equatorial plate Anaphase 1 Each chromosome separates from its homologue (pair) Move to opposite poles ○ The separation is called segregation The chromosomes do not separate at the centromere (point where sister chromatids are attached to each other) Telophase 1 Nucleus reforms around chromosomes that are still composed of sister chromatids ○ Chromosomes in the two nuclei are not identical ○ Each nuclear contains one member of the pair Cytoplasm divides (cytokinesis occurs) Meiosis 2 Very similar to mitosis (but with half the number of chromosomes) Prophase 2 Nuclear membrane dissolves Metaphase 2 Chromosomes line up along equatorial plate Anaphase 2 Sister chromatids are separated and move to opposite poles Telophase 2 Nucleus reforms Cytoplasm separates leaving 4 haploid daughter cells Cytokinesis: Cytokinesis is the final step of cell division, occurring after mitosis or meiosis, during which the cytoplasm of the parent cell is divided into two daughter cells. This process ensures that each daughter cell receives its own share of the cytoplasm, organelles, and other cellular contents, allowing them to function independently. It is essential for the completion of cell division. Without it, the two nuclei produced by mitosis or meiosis would remain in the same cytoplasm, unable to function properly as separate cells. Chromatin vs Chromatid Chromatin: Loose, thread-like form of DNA and proteins in the nucleus of a non-dividing cell. It allows for gene expression and DNA replication. Chromatid: Condensed, replicated form of DNA during cell division. Two chromatids (sister chromatids) make up a chromosome, joined at the centromere. Sister Chromatids vs Homologous Chromosomes: Sister Chromatids: Identical copies of a chromosome, joined at the centromere, created after DNA replication. They are separated during mitosis or meiosis II. Homologous Chromosomes: Paired chromosomes, one from each parent, that have the same genes but may carry different alleles. They pair up during meiosis I. ○ They have the same gene sequences, shae and size by they can carry different alleles Tetrad: When foursome of chromatids that form when replicated homologous chromosomes align Crossing over: the exchange of DNA between paired homologous chromosomes (one from each parent) that occurs during the development of egg and sperm cells (meiosis). Role of spindle fibres: Spindle fibers help move and separate chromosomes during cell division. Segregation in meiosis: Segregation is the separation of homologous chromosomes and their alleles into different gametes during meiosis, ensuring genetic diversity. Gamete Production and Sex Cells Spermatogenesis vs oogenesis: Spermatogenesis: leads to the formation of sperms Production of 4 functional sperm (haploid) Spermatogenesis begins at puberty and continues throughout life Sperm being produced in large numbers Oogenesis: helps in the formation of ova Production of 1 functional egg per cycle, and usually two or three polar bodies (non-functional) that discard/disappear is cyclic, with only one egg released per menstrual cycle. cytoplasm is not divided equally so that one egg has ample nutrients (one super healthy egg is better than 4 alright eggs) Menopause: When period stops for good Marks the end of women's menstrual cycles and fertility It is diagnosed after a woman has gone 12 consecutive months without a menstrual period typically occurring between the ages of 45 and 55 Autosomes: are the non-sex chromosomes that carry the majority of an organism's genetic information. Abnormal Meiosis: Nondisjunction Nondisjunction: Occurs when two homologous chromosomes move to the same pole during meiosis Results in one daughter cell with an extra chromosome and one lacking a chromosome ○ The condition of having an abnormal number of chromosomes = aneuploidy Can occur during mitosis (with little effect) or meiosis (with much greater effect) ○ Mitosis only one cell in trillions but meiosis the gamete cells can fertilize and make a multi-celled organism that has a genetic disorder (sperm + egg -> can fertilize) Radiation greatly increases incidence of nondisjunction Trisomy: Three chromosomes in the place of a normal pair (e.g. human with 47 chromosomes) Monosomy: Single chromosome in the place of a normal pair (e.g. human with 45 chromosomes) Polyploidy: More than two complete sets of chromosomes Occurs when all the chromosomes move to the same pole Common in plants e.g. ferns, wheat, apples, bananas, corn potatoes ○ Can give rise to new species Goldfish, salmon, salamanders, and some lizards are polyploids ○ They can reproduce asexually through parthenogenesis (embryo develops without fertilization) Nondisjunction Disorders: In humans, most meiotic nondisjunction are lethal and usually lead to miscarriage Down syndrome: trisomy of chromosome 21 Have round face, enlarged tongue, large forehead, mild to moderate intellectual disability, heart and thyroid problems, may have infertility Increased age of mother increases incidence (older = chances increased) Turner syndrome: Monosomy of sex chromosomes (XO) Female with one X chromosome Appear female but don’t usually develop sexually Tend to be short, have thick necks and broad chests Fetuses usually miscarry before 20th week Klinefelter syndrome: XXY Appear male but produce low testosterone levels at puberty (results in more feminized appearance) Usually sterile (infertile) may have language problems XXY syndrome: No unusual physical or medical problems but are often taller Increased risk of learning difficulties, delayed speech and language skills Triple-X syndrome: No unusual physical or medical problems but are often taller Increased risk of learning difficulties, delayed speech and language skills May result in infertility Karyotype: A karyotype is an individual's complete set of chromosomes, used to check the chromosomes in your cells to: See whether you have a full set of 46 chromosomes. Mendelian Genetics: Mendel: Austrian monk Discovered the basic principles of heredity through experiments with pea plants. He identified that traits are inherited as discrete units (now known as genes) and follow predictable patterns. Mendel's work laid the foundation for the science of genetics by showing how traits are inherited in predictable ways. Allele: An allele is a version of a gene that determines a particular trait. -> for each single-gene trait, one from each parent, Organisms have two alleles -> each gamete carries one allele for each gene. Mendel’s three laws: 1. Law of Segregation: Each individual has two alleles for a gene (one from each parent), and these alleles separate (segregate) during gamete formation (meiosis). Each gamete gets only one allele from each gene pair. 2. Law of Independent Assortment: Describes how different genes independently separate from one another when reproductive cells develop. The allele a gamete receives for one gene does not influence the allele received for another gene. 3. Law of Dominance: When two different alleles for a gene are present (heterozygous), the dominant allele will mask the expression of the recessive allele. The dominant allele determines the organism’s trait, while the recessive allele remains hidden unless the organism is homozygous recessive. In genetics, what does “F1 mean”? first filial generation (first generation of offspring) -> filial = Latin word offspring Genotype vs Phenotype: Genotype: The genetic makeup of an organism, representing the alleles it carries for a particular trait (e.g., Pp for flower color). Phenotype: The physical expression or appearance of a trait, determined by the genotype (e.g., purple flowers for a Pp genotype). Homozygous vs heterozygous: Homozygous = two identical alleles (e.g., AA or aa). Heterozygous = two different alleles (e.g., Aa). When would a…be used? Punnett square: to predict the genetic outcomes and the probability of different genotypes and phenotypes in offspring. Pedigree: To trace the inheritance of genetic traits, to predict the likelihood of genetic conditions and to identify carriers of recessive traits Symbols in a pedigree: Circles represent females. Squares represent males. Shaded shapes indicate individuals who express the trait or condition. Unshaded shapes represent individuals who do not express the trait. Incomplete dominance vs codominance: Incomplete dominance: The heterozygote shows a blend of the two alleles (e.g., pink flowers from red and white). 3 phenotypes Both alleles are functional (no broken ones = no recessive) Codominance: Both alleles are expressed equally and separately in the heterozygote (e.g., AB blood type with both A and B markers). Both alleles contribute equally and visibly to the organism's phenotype. Both alleles are expressed at the same time, but they do not blend. More than one can be dominant at same time and one recessive that can get hidden Sex linked traits: Autosomal traits and sex-linked traits: Autosomal traits: Traits are located on the autosomes, which are the non-sex chromosomes (chromosomes 1–22 in humans) Follows Mendelian inheritance (both males and females have two copies of each autosome) Both males and females can inherit and express autosomal traits equally Sex-linked traits: The genes for sex-linked traits are located on the sex chromosomes (X and Y chromosomes). Recessive traits on the X chromosomes: More common in males; Y-linked: Only males inherit Males are more likely to express X-linked recessive traits because they have only one X chromosome (e.g., color blindness is more common in men). Females must inherit two copies of a recessive X-linked allele (one from each parent) to express the trait, but they can be carriers if they inherit only one recessive allele. X chromosome vs Y chromosome: X: Larger, contains between 800 and 900 genes, carries genes for various biological functions, including brain and immune function Y: Smaller, contain around 72 (including the SRY gene that makes males male), determines male sex Sex linked disorders examples: Colour blindness, Duchenne muscular dystrophy, hemophilia Recessive lethal: Trait that , when both recessive alleles are present, results in death or severe malformation of the offspring Occurs most often in males due to sex-linkage ○ E.g. Muscular dystrophy Barr body: An inactive X chromosome in cells with more than one X chromosome (females) ○ A small number of genes remain active Occurs early in embryo development and is random in mammals Not all cells have the same X chromosome deactivated Can lead to a mosaic phenotype (e.g. calico cat) Without the Barr body (and the inactivation of one X chromosome), females would have too much gene activity from the X-linked genes, potentially leading to imbalanced gene expression and cellular problems. By turning off one X chromosome in each cell, females maintain proper gene dosage. Ensuring equal gene expression between males and females. What are fruit flies used for genetics experiments? short life cycle, large number of offspring, simple genetic makeup, observable traits, and low cost. Artificial insemination vs in vitro fertilization: Artificial insemination: Sperm is placed in the female reproductive tract ○ There is no sexual intercourse  Used mostly with sperm donors and livestock breeding In vitro fertilization: Egg cells are removed from the ovaries and are fertilized by sperm outside the body The embryo is then transferred to the uterus Recombinant DNA: refers to DNA molecules that have been artificially created by combining genetic material from different sources created by inserting a foreign gene into an organism E.g. BT corn contains a gene from a soil bacterium that produces a protein that kills corn borers (a moth larva) Gene therapy: Inserting genes into an individual's cells to treat genetic diseases Why is plant cloning generally much easier than animal cloning? Plants are easily cloned by taking root/stem cuttings or using tissue cultures, animal cloning, like somatic cell nuclear transfer (SCNT), is complex and often has high failure rates. Most plant cells can regenerate into a whole organism, while animal cells are typically specialized and cannot do this easily. For animals, if the cell is specialized some genes may be permanently turned off, and it requires turning on all the genes to clone animals When the nucleus is totipotent (able to support the development of an egg into an adult) meaning that it comes from an unspecialized cell, it has a higher success rate. Reasons for using biotechnology in agriculture: Increased Crop Yields: Genetically modified (GM) crops can be engineered to resist pests, diseases, and harsh environmental conditions, leading to higher productivity. Pest and Disease Resistance: Biotechnology can create crops that are resistant to insects, fungi, and viruses, reducing the need for chemical pesticides. Improved Nutritional Content: Genetic modification can enhance the nutritional value of crops, such as increasing vitamin or mineral content. Drought Tolerance: Biotechnology can create crops that withstand drought conditions, helping secure food supplies in areas with water scarcity. Dolly the sheep: lab procedures used: Using somatic cell nuclear transfer (SCNT) The nucleus was taken from a cell from the mammary gland of a Finn Dorset sheep and put into an empty egg cell from a Scottish Blackface Sheep. The egg, now containing the somatic cell nucleus, was stimulated with electricity to begin dividing and developing into an embryo.  Once normal development was confirmed in a lab at six days, the embryo was transferred into a surrogate mother. After the pregnancy, Dolly was born as a genetically identical clone of the sheep that provided the somatic cell. Why is cloning of adult somatic cells harder than embryonic cells? Epigenetic reprogramming: When a somatic cell is used for cloning (like in somatic cell nuclear transfer), the nucleus from the differentiated adult cell must undergo a reprogramming process to revert to a pluripotent state, capable of forming a whole organism. This reprogramming often fails or is inefficient because somatic cells have acquired epigenetic modifications during differentiation, which need to be reset. Differentiation: The process by which unspecialized stem cells become specialized in structure and function. Adult somatic cells are highly differentiated, making them more difficult to reprogram than embryonic cells, which are less specialized. Ethical issues surrounding the use in vitro fertilization: Embryos are potential lives and it’s inhuman to experiment on them when they can use adult stem cells instead. Allowing adoption of embryos will only influence the practice of creating more embryos than needed, many religions go against it as it’s not natural Can be used to check embryos and plant certain ones (e.g. gender) They usually produce a dozen or more embryos but only implant two and three that seem most likely to survive in the womb -> a lot of embryos unused (surplus frozen embryos) are destroyed or go to waste Physically painful -> woman must inject themselves with so many hormones to stimulate egg production Background checks may start to be required -> selection of families that do not donate to (race, intelligence, wealth)