Population Genetics and Evolution AP Biology Population Genetics

Population Genetics and Evolution AP Biology

Population Genetics n Macroevolution: evolution on a grade scale n n Ex. Evolution of a new species - modern camel Microevolution: change in the gene frequency within a population over time n Ex. Peppered moths during the Industrial Revolution

Genetics Language Review n Alleles - alternate forms of a gene n Ex. Height in plants - T = tall and t = short n n Alleles can be dominant or recessive Locus (pl. loci) - location of a gene on a chromosome Homozygous - two alleles are identical (tt) Heterozygous - two alleles are different (Tt)

Genetics Language Review cont… n n n Genotype - genetic make-up of an individual Phenotype - physical and physiological traits of an individual Incomplete Dominance - neither of the alleles are dominant and blending occurs n n red, white and pink flowers Co-dominant - both alleles for the trait are dominant n black, white and black-white feathers in chickens

Genetic structure of a parent population of field mice Phenotype Black Mice White Mice Genotype AA Aa aa Number of Mice 196 168 36 (total # of mice = 400) Genotype Frequencies Number of Alleles in Gene Pool (total = 800) Allele Frequencies XXXXXXXX

Phenotype Purple White Genotype AA Aa aa Number of Flowers 320 160 20 (total # of flowers = 500) Genotype Frequencies Number of Alleles in Gene Pool (total = 1000) Allele Frequencies XXXXXXXX

The Hardy-Weinberg Principle n A way to determine how real populations change over time by developing a model of a population that does not change genetically from one generation to the next n n Actual populations can be compared to the hypothetical model If proportions of genotypes do not change from generation to generation, the genotypes are said to be in Hardy-Weinberg Equilibrium

The Hardy-Weinberg equation: 2 p + 2 pq 2 +q =1

Where: n n n p = frequency of dominant allele (ex. A) q = frequency of recessive allele (ex. a) p 2 = frequency of individuals homozygous for allele A 2 pq = frequency of individuals heterozygous for alleles A and a q 2 = frequency of individuals homozygous for allele a

Example: The dominant allele in a population has the frequency of 0. 6 n A) Find the frequency of the recessive allele n n NOTE: p + q = 1 (allele frequency) B) Find the frequencies of the genotypes in this population. n NOTE: p 2 + 2 pq +q 2 = 1 (genotypic frequency)

Solution:

Conditions for Hardy. Weinberg 1. 2. 3. 4. 5. The population is large (unaffected by random gene changes) Mating is random Isolation (no gene flow between populations) No mutations No natural selection (no genotype has a reproductive advantage over another)