Population Genetics

Population Genetics Chapter 23.1

Quick Review: Natural Selection Variation  Natural Selection  Speciation Organisms better suited to the environment SURVIVE & REPRODUCE at a greater rate than those less suited to the environment and this is how… SPECIES EVOLVE

Quick Review: DNA & Mutations A change in genetic material may change a protein Mutation  Variation  Natural Selection  Speciation

Hardy & Weinberg Mutation  Variation  Natural Selection  Speciation I love math! We can study variation at the molecular level AKA: mutations

Gene Pools Collection of genes within a population of a species

Hardy & Weinberg We can study changes in phenotypes of one trait in a population over time We can convert phenotypes into genotypes Thus, a math equation will show if evolution is occurring We can calculate allele frequencies based upon the genotypes

Ex: Allele Frequencies in Snapdragons • Collect data of phenotypes of a population • 320 red flowers, 160 pink flowers, & 20 white flowers • Convert phenotypes to genotypes • 320 RR • 160 RW • 20 WW • Calculate allele frequencies • R alleles = 320 +320 + 160 = 800 • W alleles = 20 + 20 + 160 = 200

Ex: Allele Frequencies in Snapdragons • Allele Frequency • 800 R alleles / 1000 total alleles (80% or 0.8) • 200 W alleles / 1000 total alleles (20% or 0.2)

Ex: Allele Frequencies in Snapdragons • Hardy-Weinberg: • If evolution is not occurring in this population • Then allele frequency will remain constant over time • Therefore at any moment the population will have: • 80% R alleles & 20% W alleles • If 10 years later: • 50% R alleles • 50 % W alleles • Then microevolution is occurring

Applying H.W.E. • This happens to nearly all populations for all traits • p represents the dominant allele (R) • q represents the recessive allele (W) p = .8 & q = .2 p + q = 1

Solve this story problem In certain Native American groups, albinism is due to a homozygous recessive condition. The frequency of the allele for this condition is currently .06 of the Native American population. What is the frequency of the dominant allele? p + q = 1 P + .06 = 1 p = .94

Extrapolating H.W.E. • H.W.E. Equation 1: • p + q = 1 (shows allele frequencies) • H.W.E. Equation 2: • (1) * (1) = 1 • (p + q) * (p + q) = 1 • p2 +2pq + q2 = 1 • 500 Snapdragon Example • p = .8 & q = .2 • (.8)2 +2(.8*.2) + (.2)2 = 1 • .64 + .32 + .04 = 1 • 320 + 160 + 20 = 500

Applying H.W.E. p2 = homozygous dominant condition 2pq = heterozygous condition q2 = homozygous recessive condition p2 +2pq + q2 = 1 RR + 2RW + WW = 1

Solve this story problem In a certain flock of sheep, 4 percent of the population has black wool (recessive condition) and 96 percent has white wool. What % of sheep are heterozygous for wool color? p2 +2pq + q2 = 1

H.W.E. Conditions • Our equations are great for: • Finding allele frequencies: p + q = 1 • Finding genotype frequencies: p2 +2pq + q2 = 1 • Showing microevolution if values change over time • When would allele frequencies not change over time?

H.W.E. Conditions • No Mutations • No new genotypes/phenotypes • Very large population size • No minor population disruptions (genetic drift) • Isolation from other populations • No immigration/emigration (gene flow) • Random Mating • No picky females choosing one allele over another • No natural selection • No environmental pressures selecting one allele over another

Population Genetics