Unit 5 Heredity AP BIO

Prophase I

• Synapsis and crossing over/recombination occurs

• Exchange of DNA between homologous chromosomes, leading to genetic variation

Metaphase I

• Tetrads (homologous pairs) line up at the metaphase plate

• Independent Orientation - Tetrads line up at the metaphase plate

Anaphase I

• Homologous pairs separate

  • Sister chromatids are STILL attached, tetrads separate

Synapsis

• Homologous chromosomes pair up and physically connect to each other forming a tetrad

Crossing over/Recombination

• Occurs at the chiasmata (ends of chromosomes)

• Exchanges DNA between the homologous

• Every chromatid produced has a unique combination of DNA

Chiasmata

• The tips/hands of chromosomes where crossing over occurs during meiosis.

Telophase I & Cytokinesis

• Nuclei and cytoplasm divide

• Creates a haploid set of chromosomes in each daughter cell

Prophase II

• No crossing voer

• Spindle forms

Metaphase II

• Chromosomes line up at the metaphase

• Chromatids are unique

Anaphase II

• Sister chromatids separate and move towards opposite poles

Telophase II & Cytokinesis

• 4 haploid cells

• Nuclei reappear

• Each daughter cell is genetically unique

Genetic Variation (Meiosis)

• Plays a role in natural selection!!

• Crossing over

  • Produces recombinant chromosomes; they exchange genetic material

• Independent assortment of chromosomes

  • Chromosomes are randomly oriented along the metaphase plate

• Random Fertilization

  • Any sperm can fertilize any egg

True Breeding

• Organisms that produce offspring of the SAME variety over many generations of self pollination

P Generation

• The parental generation in a breeding experiment, typically homozygous for a trait. This generation is used to produce the F1 generation.

F₁ Generation

• First Filial

• Hybrid offspring of P generation

F₂ Generation

• Second FIlial

• Offspring of F1 generation

Allele

• The specific version of a singular gene

  • e.g. brown eye color and blue eye color

Dominant Trait

• Always expressed

Recessive Trait

• Not always expressed

Homozygous

• An organism that has a pair of identical alleles for a character

  • Dominant - AA

  • Recessive - aa

Heterozygous

• An organism that has two different alleles for a gene

  • e.g. Aa

Genotype

• The genetic makeup (alleles) of an organism

Phenotype

• An organism’s physical appearance, determined by their genetic makeup

Testcross

• ALWAYS with a homozygous recessive

• Used to determine the genotype of a gene

  • e.g. (rr) crossed with (R?) to figure out if it is homozygous dominant or heterogenous

The Law of Segregation

• The two alleles for each gene will separate during meiosis, as diploid cells become haploid

• This ensures that each gamete receives only one allele for each gene, leading to genetic diversity in the offspring

The Law of Independent Assortment

• Alleles of genes on non-homologous chromosomes will separate during Meiosis I WITHOUT influencing each other

• The inheritance of one trait will not affect the inheritance of another trait, leading to genetic variation among offspring

Aneuploidy

• An abnormal chromosome number

Monosomy

• A type of aneuploidy

• A single copy of a chromosome

Trisomy

• A type of aneuploidy

• Three copies of a chromosome

Shortened Chromosomes

• A form of chromosomal abnormality

• Usually occurs from breakage or improper recombining of genetic information

Lengthened Chromosomes

• A form of chromosomal abnormality

• Usually occurs from accidental duplication of segments of genetic information

Autosomal Dominant

• A pattern of inheritance where only one copy of an altered gene is sufficient to cause a genetic disorder

• Offspring have a 50% chance of inheriting the trait if one parent carries the dominant allele

Autosomal Recessive

• A pattern of inheritance where two copies of an altered gene are needed to cause a genetic disorder

• Offspring have a 25% chance of inheriting the trait if both parents are carriers of the recessive allele

Non-Nuclear DNA

• Traits found on either the mitochondria or chloroplasts

• Both chloroplasts and mitochondria are randomly assorted to gametes and daughter cells

  • In animals mitochondria are transmitted by the egg, NOT the sperm

    • ALL mitochondrial DNA is maternally inherited

  • In plants, mitochondria and chloroplasts are transmitted in the ovule, NOT the pollen

    • Both mitochondrial and chloroplast determined traits are maternally inherited

Chi-square

• A form of statistical analysis used to compare the actual results (observed) with the expected results

  • Helps determine whether data obtained experimentally provided a “good fit” to the expected data

  • Helps determine if deviation results are random or statistical

Observed Values

• The numbers that you get in your data

• Usually no calculations

Expected Values

• Based on probability

• Requires calculations

Genotypic Ratio

• Homozygous Dominant ratio → Heterozygous Ratio → Homozygous Recessive Ratio

  • e.g. 1:2:1 (Rr + Rr)

Phenotypical Ration

• Ratio with trait → Ration w/o trait

  • e.g. 3:1 (brown v. blue eyes)

Phenotypic Plasticity

• The flexibility of phenotypein response to environmental changes, allowing organisms to adapt to varying conditions

Nondisjunction

• Chromosomes fail to separate properly in meiosis I or meiosis II

• This results in gametes with abnormal numbers of chromosomes, potentially leading to conditions like Down syndrome

Homologous Chromosomes

• A pair of chromosomes with the same size, length, and centromere position

• Carries the SAME genetic information

  • One chromosome from mama, one from papa

Autosomes

• Chromosomes that do not determine sex

Sex Chromosomes

• X and Y chromosomes

  • Eggs: X (humans - 22 + X)

  • Sperm: X or Y (humans: 22 + X OR 22 + Y)

• ALL reproduced organisms have a diploid and a haploid number!

Fertilization

• When a sperm cell (haploid) fuses with an egg (haploid) to form a zygote (diploid)

Life Cycle

• Sequence of stages in the reproductive history of an organism from conception to its own reproduction

• Fertilization and meiosis ALTERNATE in sexual life cycles

Meiosis

• A process that creates haploid gametes from diploid cells through two rounds of cell division, resulting in genetic diversity

Crossing Over/Recombination

• Produces recombinant chromosomes that exchanges genetic material

Independent Assortment

• Chromosomes are randomly oriented along the metaphase plate during metaphase I

• They can orient with the maternal or paternal chromosomes closer to a given pole (random!)

Random Fertilization

• Any sperm can fertilize any egg

Heredity

• The transmission of traits from one generation to the next

• Traits are passed from parent to offspring through genes and DNA, which serve as the fundamental units of heredity

Gene Pool

• A populations genetic makeup

  • Consists of all copies of every type of allele

Micro evolution

• Small scale genetic changes in a population

Mutations

• Changes in DNA

• CAN result in genetic variation

• Rates tend to be slow in plants and animals and fast in prokaryotes due to faster generation time

  • Asexual reproduction more common in prokaryotes → Shorter generation time

• Can be harmful, neutral, or beneficial

Osmotrophs

• Food source comes from environment around them

  • Diffusion or transport

• Common in prokaryotes

• Very environment dependent → Bad environment = death

Genetic Drift

• Chance events that cause a change in allele frequency from one generation to the next

  • Can lead to a loss in genetic variation rates

  • Can cause harmful alleles to become fixed

  • Most significant to small populations

Bottleneck Effect

• When a large population is drastically reduced by a NON-SELECTIVE distaster

  • Flood, famine, fires, hurricanes, hunting etc.

• Some alleles may become overrepresented, underrepresented, or absent

Founder Effect

• When a few individuals become isolated from a large population and establish a new small population with a gene pool that differs from the large population

  • Loses genetic diversity

Gene Flow

• The transfer of alleles into or out of a population due to fertile individuals or gametes

  • Emigration/Immigration

Relative Fitness

• The number of surviving offspring that an individual produces compared to the number left by others in the population

Directional Selection

• Selection towards one extreme phenotype

Stabilizing Selection

• Selection towards the mean and against the extreme phenotypes

• Disruptive Selection

• Selection against the mean, both phenotypic extremes have the highest relative fitness

Sexual Selection

• A type of natural selection that explains why many species have unique/showy traits

Hardy Weinberg Equilibrium

• Used to assess whether natural selection or other factors are causing evolution at a particular locus

• Determines what the genetic makeup of the population would be if it were NOT evolving