Animal Genetics Exam 2

Population Genetics

_____: The study of populations over time with particular attention paid to the genetic structure.

Populations

Population Genetics

_____: Group of individuals of the same species that can interbreed.

Genetic Structure

Population Genetics

_____: Alleles (A,a) & Genotypes (AA, Aa, aa) → Gene and genotypic frequencies

• Allele and gene frequency mean the same thing.

Gene Frequency

________: proportion of the total loci for a particular allelic series occupied by a particular allele.

abundance

Gene Frequency

• The relative ____ or rarity of an allele in a population as compared to the other alleles in that population.

probability

Gene Frequency

• Also the _______ of any one gamete carrying a particular gene.

Codominance

Example Gene Frquency : Coat color in cattle

RR= Red

Rr = Roan (Mixture)

rr= White

• R = r (this is an example of _______, which is seen when both alleles are expressed)

Gene Frequency

• The probability of drawing the gene at random from all possible genes at that locus in the population.

• Assume a herd of 500 Shorthorns:

  • 130 reds, 265 roans, and 105 whites.

    • What are the frequencies?

    • How many total genes/alleles?

    • How many red alleles?

    • Frequency of the red and white allele?

codominance

Gene and Genotypic Frequency

• With _____ (like past example) → easy to calculate frequencies (both gene and genotypic)

  • Both alleles in a heterozygote are fully expressed, with niether one being dominant or recessive to the other.

Gene Frequencies Summary

Gene Frequencies Summary

One to One

Gene or Genotypic Frequency

Codominance

• _________ relationship between the phenotypes and genotypes → each genotype expresses one phenotype.

• Easy calculations of gene and genotypic frequencies.

NOT

Gene or Genotypic Frequency

Dominance

• ____ a one-to-one relationship

• calculations of gene and genotypic frequencies are NOT straightforward

assumptions

Dominance

• Cannot separate the two dominant genotypes unless we evoke some ____

Hardy-Weinberg Law

_________ (1908)

• In a large, random mating population, in the absence of forces which change gene frequencies, both gene and genotypic rations ratios remains constant from one generation to the next.

Hardy-Weinberg Equilibrium

If a population meets the conditions of the Hardy-Weinberg Law the population is said to be in ____________

Large population

Hardy-Weinberg Lab (1908)

**Assumptions for this to true:

1. __________ - ensures limited change by chance alone (genetic drift)

equal opportunity

2. Random mating - every individual has an _________ of mating with another individual of the opposite gender. Defined by TRAIT, not SPECIES.

• Mutation

• Migration

• Selection

3. No forces to change gene frequency

• (______, _______, ________)

heritable change

Forces that can change Gene Frequency

1) Mutation - sudden ______ (happens all the time) in genetic material

• at equilibrium theoretically no mutations are occuring.

breeding animals

Forces that can change Gene Frequency

2) Migration - movement of ____ animals from one population to another.

genotypes, phenotypes

Forces that can change Gene Frequency

3) Selection (artifical or natural) - relative success in becoming a parent based on ______ or ______.

• **all genotypes and phenotypes are able to mate.

p

Nomenclature

• __ = f(D) → frequency of dominant allele

q

Nomenclature

• _____ = f(d) → frequency of recessive allele

1

p + q = ____

p²

Genotype - DD

Frequency - ___

2pq

Genotype - Dd

Frequency - ____

q²

Genotype - dd

Frequency - ____

H-W equilibrium

Assuming ____________ we can now press on

Review Math

Review Math

• p

• p²

At Equilibrium

With a generation:

• there is a relationship between gene and genotypic frequencies such that if the f(A) is ____ then f(AA) is ____

constant

At Equilibrium

Across generations:

• gene and genotypic frequencies remain _____

  • If a population is at equilibirum and there are no forces gene and genotypic rations remain the same year after year (generation after generation)

At equilibrium review

At equilibrium review

randomly

Important to know when and if a population is in equilibirum!

• Assume a population not in equilibrium begins to mate _____.

• How does this affect the gene and genotypic frequenciesn at autosomal loci?

one generation

Returning to Equilibrium

• For any single autosomal locus, with any number of alleles, it takes just _______ of random mating for a population to return to equilibrium.

  • Condition: IF the allele freqeuncies are the SAME IN MALES AND FEMALES!

two generations

Returning to Equilibrium (Autosomal Locus)

• When allele frequences in males and females are NOT the same, returning to equilibrium requires _________ of random mating.

avergae

Two Generations of Random Mating

1. In the first generation, male and female gene frequencies become equal to the ____ of the frequencies in the parents.

equilbrium

Two Generations of Random Mating

2. In the second generation the population reaches _____.