Sexual and Asexual Reproduction

Reproduction

• Organisms overcome dying and perpetuate their species through reproduction
• There are two types of reproduction: sexual and asexual

Sexual Reproduction

• Requires two different organisms
• Offspring are created through the fusion of two sex cells: spermatocytes and oocytes

Asexual Reproduction

• Only needs one organism
• Offspring are created through separation

Union of Gametes

• Involves two types: isogamy and heterogamy
• Isogamy occurs when Chlamydomonas produces gametes or Spirogyra undergoes conjugation
• Heterogamy can be seen in animal sperm and egg

Special Terms for Sexual Reproduction:

• Bisexual Reproduction
• Hermaphrodites

Cycles

• Gametophyte: A plant (or the haploid phase in the life cycle)
  • Produces gametes by mitosis to produce a zygote
  • Describes as the Haploid generation
• Sporophyte: A plant (or the diploid phase in the life cycle)
  • Produces spores by meiosis to produce gametophyte
  • Describes as the Diploid generation
• Syngamy: The fusion of two gametes to form a zygote

Asexual Reproduction Characteristics

• Number of parents involved: One
• Gametes: There is no need for gamete union
• Genetic Composition: Genetically identical to the parent
• Offspring: Clone

Sexual Reproduction Characteristics

• Number of parents involved: Two
• Requires sperm to fertilize the egg
• Genetic Composition: Generally hybrids of parents

Stages of Fertilization Life Cycles

• Haplontic Life cycle:
  • The haploid stage (gametophyte) is multicellular
  • The only diploid stage is the fertilized egg cell
  • Sporophytic generation is represented only by the one-celled zygote
  • No free-living sporophytes exist
  • Meiosis in the zygote results in the formation of haploid spores
• Diplontic life cycle:
  • The diploid stage (sporophyte) is multicellular
  • The haploid stage (gametophyte) is represented by the single-celled gametes
• Haplodiplonotic life cycle:
  • Occurs in marine algae and plants
  • Involves two multicellular individuals
    • The diploid zygote forms a sporophyte
    • Gametophytes are produced by spores
    • Gametes form a diploid zygote

Floral Morphology

• Receptacle (Torus): shortened, conical, or disk-shaped at the upper end of the stalk of the flower

Floral Organs

• The four sets of floral organs are the calyx, corolla, stamens, and pistil
  • Calyx, corolla, and receptacle are accessory organs
• Stamen and pistil are essential organs

Calyx

• Outermost green leaf-like structure
  • Sepal - a lobe of the calyx
  • Gamosepalous - sepals are united forming a tube
  • Polysepalous - sepals are free from one another

Corolla

• Inside the calyx with bright colored, delicate petals
  • Gamopetalous - petals are united forming a corolla tub
  • Polypetalous - petals are free from one another
  • Hypogynous - corolla arises from the receptacle below the ovary
  • Epigynous - corolla originates from the top of the ovary
  • Perigynous – corolla borne on the calyx
  • Perianth - when there are petals of the same structure and color
• Sepals enclose the outer flower parts in the bud and are generally green
• Petals are the conspicuous, colored, and attractive part of a flower

Stamens

• The male germ cells/sperms/part of the flower
  • The grouping of the stamens is called androecium
    • Filament
    • Anther

Pistil

• Found at the center and considered the female part of the flower
  • Collectively known as gynoecium
    • Ovary – stout basal portion containing ovules
    • Style – slender structure on top of the ovary
    • Stigma – the enlargement at the tip of the style
• The stigma receives a sticky viscid substance, which helps in pollination -The style is the passage of the sperm of the nuclei in going to the ovary to fertilize the egg cell

Plant Sources

• Monoecious plants:
  • Staminate and pistillate flowers exist on the same plant.
  • Example: Squash and corn
• Dioecious plants:
  • Staminate and pistillate flowers exist on separate plants
  • Example: Papaya

Pollen Development

• Stamen which consists of the filament and anther, makes up the male parts
• The anther is the location where pollen is produced

Egg Development

• Carpel, consisting of the stigma, style, and ovary, are the female part
• The ovary contains the ovules
• The megaspore mother cell undergoes meiosis, and produces megaspores
• Typically, only one megaspore survives during disintegration
• Three rounds of mitosis, but only 7 cells are formed

Pollination

• Involves the transfer of pollen grains from the anther to the stigma
• Self-pollination occurs when pollen grains are transferred from the anther to the stigma of the same flower
• Cross-pollination occurs when pollen grains are transferred from the anther of a flower on one plant to the stigma of a flower on another plant

Types of Flowers (Based on the Agent of Pollination)

• Entomophilous flowers are insect pollinated flowers
  • Modifications include bright color, scent, possess sticky pollen/spiny pollen, sticky stigmas, and produce nectar
• Anemophilous flowers are wind pollinated flowers
  • Modifications include inconspicuous flowers lacking scent, small and dry pollen grains, expanded stigmas, and do not produce nectar
• Hydrophilous flowers are water pollinated flowers
  • Modifications are similar to wind-pollinated flowers
• Zoophilous flowers are animal-pollinated flowers
  • Modifications are similar to entomophilous flowers

Fertilization

• After pollen is transferred from the anther to the stigma, one of the two cells in the pollen grain grows a thin pollen tube down through the style into the ovule in the ovary
• The second cell divides to create two male gametes/sperm cells, which then move down the pollen tube and enter the ovule
  • Double fertilization then occurs
    • One sperm fuses with the egg to make a zygote
    • One sperm fuses with the endosperm mother cell to make triploid endosperm
    • Synergids will disintegrate
• Post-fertilization, the ovule develops into a seed, and the ovary surrounding it develops into a fruit

Seed Germination

• The seed undergoes imbibition to break dormancy
• Nutrients stored in the endosperm or cotyledons are digested and transferred to the growing regions of the embryo
• Epigeal Germination

Gas Exchange/Respiration

• The uptake of molecular oxygen from the environment
• The discharging of carbon dioxide to the environment
• Often called the respiratory exchange
• Oxygen is needed in tissues for aerobic respiration to occur and extract ATP from food
• Carbon dioxide must be released to prevent physiological pH in tissues from being acidic

Principles Influencing Gas Exchange

• The environment should be moist and large enough
• Prevent desiccation

Diffusion of Gases

• Respiratory systems rely on the diffusion of gases down pressure gradients -Fick’s Law governs the amount of diffusion of a gas across a membrane
  • The amount of diffusion is proportional to the surface area and difference in partial pressure between the two sides
  • The amount of diffusion is inversely proportional to the thickness of the membrane

Surface-to-Volume Ratio

• As an animal grows, the surface area increases at a lesser rate than its volume causing making diffusion of gases into the interior more difficult
• Animals must have a body design that keeps internal cells close to the surface
• Animals must have a system to remove the gases inward

Ventilation

• Refers to the movement of the respiratory medium (air or water) over the respiratory surface
• Bony fishes move the gill covers (operculum) for water carrying oxygen to flow the gills
• In humans, the muscles of the thorax contract to expand and contract the chest cavity to allow air to move in and out of the lungs

Factors Affecting the Rate of Diffusion

• Temperature
  • Increase in Temperature causes increased rate of diffusion
• Molecular Mass
  • Decrease in Molecular mass causes increased rate of diffusion
• Thickness of barrier
  • Increased (Thicker) cell wall causes decreased rate of diffusion
• Concentration gradient
  • Increased Concentration gradient causes increased rate of diffusion
• Surface-area-to-volume ratio
  • Increased Surface area-to-volume ratio causes increased rate of diffusion

Respiratory Pigments and Proteins

• Animal adaptations for gas exchange include respiratory pigments that bind and transport gases
• Hemoglobin is the respiratory pigment of vertebrates
• Hemocyanin is the respiratory pigment of invertebrates like arthropods and mollusks
• Blood cannot carry sufficient oxygen and carbon dioxide in dissolved form to meet the body’s requirements
• Hemoglobin helps enhance its capacity

Gas Exchange Structures in Plants

• Stomata in Leaves
• Lenticels in Stem
• Root Hairs in Aerial Roots
• Pneumatophores or Lateral Roots of Mangroves

Respiratory Surfaces in Invertebrates

• Cell surface or cell membrane
  • Used in unicellular organisms
• Integumentary exchange
  • Refers to the general body surface or skin
  • Used in animals with a high surface-to-volume ratio
• External Gills
  • Used by invertebrates that live in aquatic habitats
  • Gills are highly folded, thin-walled, and vascularized epidermis that project outward from the body
  • Example: crayfish, lobster, sea star, and nudibranch
• Tracheal System
  • Utilizes fine air-conducting tubules to provide gaseous exchange at the cellular level
  • Not dependent on a circulatory system
  • Example: insects and spiders

Respiratory Surfaces in Vertebrates

• External Gills
  • Thin, vascularized epidermis that projects from the body surface of a few amphibians
  • Example: larval salamander
• Internal Gills
  • Rows of slits or pockets in adult fishes positioned at the back of the mouth
  • Water that enters the mouth can flow over them as it exits just behind the head
    • Water flows over the gills and blood circulates through them in opposite directions
    • This mechanism, called countercurrent flow, is highly efficient in extracting oxygen from water, whose oxygen contents is lower than air
• Lungs
  • Internal respiratory surfaces shaped as a cavity or sac
  • Provide a membrane for gaseous exchange since they are not in direct contact with all other parts of the body
  • Require a circulatory
    • Air moves by bulk flow into and out of the lung
    • Gases diffuse across the inner respiratory surfaces of the lungs
    • Pulmonary circulation allows the diffusion of dissolved gases across lung capillaries
    • In body tissues, oxygen diffuses from blood, interstitial fluid, and cells
    • The pathway of carbon dioxide is in reverse
    • All lungs receive deoxygenated blood from the heart and return oxygenated blood to the heart

Breathing Mechanisms in Vertebrates

• Amphibians ventilate their lungs by positive pressure breathing which forces air down the trachea
• Birds use a system of air sacs as a blower to keep air flowing through the lungs in one direction only, preventing the mixing of incoming and outgoing air
• Mammals ventilate their lungs by negative pressure breathing, pulling air into the lungs when the volume expands muscles and diaphragm contract
  • Incoming and outgoing air mix, decreasing the efficiency of ventilation

Coordination of Gas Exchange and Circulation

• Oxygen Transport
  • Oxygen diffuses down a pressure gradient from the lungs > blood plasma > red blood cells and binds to hemoglobin to form oxyhemoglobin
  • Hemoglobin gives up its oxygen in tissues where partial pressure is oxygen is low, blood is warmer, partial pressure of carbon dioxide is higher, and pH is lower, these 4 conditions occur in tissues with high metabolism
• Carbon Dioxide Transport
  • Carbon dioxide diffuses down its partial pressure gradient from tissues into the blood plasma and RBC > air in alveoli
  • 7% is dissolved in plasma, 23% binds with hemoglobin to form carbaminohemoglobin, and 70% is in bicarbonate form
  • Bicarbonate and carbonic acid formation is enhanced by the enzyme carbonic anhydrase, which is located in the RBC

Respiration Control in Vertebrates

• The nervous system controls oxygen and carbon dioxide levels for the entire body
• Regulates the rate and depth of breathing Brain monitors the pH of the CSF through sensors
• Reflecting carbon dioxide concentration in the blood
• Secondary control is exerted by sensors in the aorta and carotid arteries
  • Monitor blood levels of oxygen and carbon dioxide by monitoring blood pH

Respiratory Adaptations

• Animals living in extreme low-oxygen environments
• Inhabit high altitudes and have larger hearts and lungs
• Hemoglobin has high affinity for binding oxygen
• Diving animals have a high amount of hematocrits, which refers to the ratio of the volume of packed RBC to the volume of whole blood
• The muscles have a high amount of myoglobin which is an oxygen-binding protein

Respiratory Problems

• Asthma
  • Involves the muscles around bronchioles that contract more than usual, increasing resistance to airflow
• Emphysema
  • An abnormal condition of the lungs marked by decreased respiratory function
  • Associated with smoking or chronic bronchitis or old age
• Smoking tobacco products is one of the leading causes of death and strongly linked to cancer, cardiovascular disease, stroke and emphysema

Genetics Terminology

• Genetics studies inherited variation transmission, expressions, and evolution of genetic information
• Heredity is the natural process by which physical and mental qualities are passed from a parent to a child

Timeline of Genetic Discovery

• Domestication of Animals and Plants was a necessary step in human societies, going from hunter/gatherer to agriculture and herding
• Ancient processes include domestication of animals like dogs, sheep, goats, oxen, horses, and camels as well as cultivation of plants such as date palms, cereal crops, rice, and corm
• Myths and Mutants
• Work with animals led to recognition of heritable traits in humans
  • Heredity is biological inheritance within the human species

Early Theories

• Theories of blending of Inheritance were disproved
• Democritus believed that tiny particles controlled inheritance of particular traits as each body part contained these particles responsible for that inheritance
  • The body part particles periodically joined to form sperm and ova.
• According to the Pangenisis theory of Jean Baptiste Lamarck from the late 18th Century, any animal or plant change after birth passed onto offspring when it reproduced
  • Modified ideas of Democritus claim that that environment could induce changes to these particles
• The theory of Preformation from the 17th Century claims that sperm and egg discovered actually contained miniatures of adults.

The Work of Gregor Mendel

• Gregor Mendel discovered genetics
• Selected pea plants for his study because they grew easily in little space exhibited observable traits, could self-pollinate or cross-pollinate, and applied math with biology

Mendel Genes and Dominance

• Mendel studied 7 different pea plants traits that exhibited specific characteristics such as seed color and height
  • Each trait had contrasting characteristics such as green seed color or yellow seed color
  • Mendel crossed plants with 7 contrasting characters
    • P (parental) generation are original generation
    • F1 generation are offspring of P generation

Mendel Experiment

• Crossed purebred tall plants with purebred short plants
  • Purebred organisms produces the same trait in offspring and is also called true breeding

Mendel Conclusions

• Biological inheritance is determined by factors passed from generation to generation called genes
• Genes occur in two contrasting forms called alleles
• Some alleles are dominant while others are recessive

The Principle of Segregation

• Mendel wanted to answer the question of whether recessive alleles disappeared or were still present in F1 plants
  • Allowed F1 hybrid plants to produce F2 by self-pollination
  • 25% of offspring showed recessive characteristics

Math Side: Probability

• Probability is the likelihood that a particular event will occur
• Alleles segregate randomly like a coin flip: 50/50 chance each time
• Punnett Square can be used to represent the possible gene combinations from a genetic cross

Definitions:

• Phenotype is the physical characteristics
• Genotype is the genetic makeup

Independent Assortment

• Mendel determined if alleles separated independently by whether the inheritance of one characteristic linked to another

Two-Factor Cross

• Mendel experimented to determine if alleles segregated independently
• His results were very close to the 9:3:3:1 ratio which proved that genes that segregate independently do not influence each other’s inheritance

Terms in Extra Information

• Parent has two copies of the genetic information (homozygous)
• Each gamete contains only one copy of the genetic information
• Random fertilization unites one copy from each parent
• The F1 progeny contains two different variants, or alleles, of the gene and are therefore heterozygous

Terms

• Pedigree: diagrams that show ancestral relationships and genetic trait transmission across multiple generations
• Allele: one of the possible alternative forms of a gene that are distinguished by phenotypic effects
• Genotype: the allelic or genetic makeup of an organism, more specifically an allelic composition of one or a limited number of genes under investigation
• Autosomes: actual chromosomes normally present inside the nucleus without considering the X and Y (sex) chromosomes
• Gene: discrete unit of inheritance believed to carry the hereditary traits
• Phenotype: the overt appearance of a genetically controlled trait
• Trait: any detectable phenotypic variation of a particular inherited character.
• Homozygous (homozygote): an individual with identical alleles for a gene or genes, producing identical gametes who breed true
• Heterozygous (heterozygote): an individual with different alleles at one or more loci who do produce unlike gametes who do not breed true
• Dominant Trait: trait with contrasting forms that appears in the offspring in a cross between two purebred individuals
• Recessive Gene: gene whose phenotype is not expressed if the dominant allele is also present

Mendelian Genetics: 1st Mendelian Law

• For every trait governed by a pair of alleles, these alleles segregate or separate during gamete formation in meiosis

Round Versus Wrinkled: Modern Context

• The gene that determines seed shape encodes starch-branching enzyme I (SBEI) that synthesizes amylopectin
• Round (W) seeds contain amylopectin and shrink uniformly when drying
• Wrinkled (w) seeds have a mutation in the starch-branching enzyme I (SBEI) and cannot make amylopectin so they shrink irregularly

Testcross Analysis

• An analysis to figure out the genotype of an organism
• The unknown pea is crossed with one known to be homozygous recessive, where phenotypes of the resulting can be attributed solely to the gene they inherited from the unknown parent
• If the unknown is WW, all the progeny of the testcross will be Ww (dominant) progeny
• If the unknown is Ww, 1/2 the progeny of the testcross will be Ww (dominant) and 1/2 the progeny will be ww (recessive)

The Principle of Independent Assortment

• States that the segregation of the members of any pair of alleles is independent of the segregation of other pairs in the formation of reproductive cells

Genetics and Probability

• The probability of two independent events, A and B, are realized simultaneously as the product of their separate probabilities
• The probability of one or the other of two mutually exclusive events, A or B, are realized as the sum of their separate probabilities

Second Mendelian Law

• A pair of alleles for one trait will segregate or separate independently of another pair of alleles for another trait during meiosis.
• The pedigree analysis determines individual genotypes and to predict how single gene traits are transmitted

Inheritance Patterns in Degrees

• Autosomal dominant
• Autosomal recessive
• X-linked dominant
• X-linked recessive
• Y-linked
• Maternal inheritance (mitochondrial inheritance)

Patterns of Inheritance

• Autosomal Dominant Inheritance Pattern
  • Due to a dominant gene on an autosome
    • Males and females are equally affected - Every affected individual has at least one affected parent - Affected individuals mating with unaffected individuals have at least a 50% chance of transmitting the trait to each child
    • Two affected individuals may have unaffected children - Phenotype generally appears every generation
  • Examples are achondroplasia, Huntington’s disease, widow’s peak, , free lobes, tongue-rolling, brachydactyly, and hypercholesterolemia
• Autosomal Recessive Inheritance Pattern
  • Due to a recessive gene on an autosome
    • Males and females are equally affected
    • An affected individual may have unaffected parents
    • All children of two affected individuals are affected
    • Phenotype may skip a generation
  • Examples are and cystic fibrosis, phenylketonuria, galactosemia, albinism, hemophilia, and sickle-cell anemia
• X-Linked Dominant Inheritance Pattern
  • Due to a dominant allele on the X-chromosome - The trait is never passed from the father to son - All daughters of an affected male and a normal female are affected - All sons of an affected male and a normal female are normal - Females are more likely to be affected than males
  • Examples are hypophosphatemia, Aicardi syndrome, and fragile X syndrome
• X-Linked Recessive Inheritance Pattern
  • Due to a recessive allele on the X-chromosome
    • The trait is never passed from father to son
  • Males are more likely to be affected than females. - The trait or disease is typically passed from an affected grandfather, through carrier daughters, to half of his grandsons
  • Examples are red and green colorblindness, hemophilia, and Duchenne muscular dystrophy
• Y-Linked Inheritance Pattern
  • Due to an allele on the y-chromosome
    • When a male is affected, all of his male children are affected
  • Examples include male infertility and hypertrichosis
• Inheritance, Maternal (Mitochondrial)
  • Transmitted through genes in the mitochondria, not inside nucleus
  • An affected mother will have all offspring affected
  • If the father is affected, NONE of the offspring will be affected
  • Leber hereditary optic neuropathy (LHON)
  • Mitochondrial encelopathy with lactic acididosis and stroke-like episodes (MELAS)