Genes and Variation EQ How is the gene

Genes and Variation EQ: How is the gene pool affected by selection pressure?

Genotype and Phenotype Genotype: particular combination of alleles Phenotype: physical, physiological, and behavioral characteristics

Allele Frequency Number of times an allele occurs in a gene pool, as a percentage of the total occurrence of alleles In 50 alleles: In 100 alleles: 40 are B (black) 20 alleles are B (black) 30 alleles are b (brown) 60 are b (brown)

Alleles in a Population Evolution involves any change in the frequency of alleles in a population over time. Mice population = 25 mice 12 4 9

Single-Gene Traits Phenotypic ratios are determined by the frequency of alleles and by whether the alleles are dominant or recessive. 77% 23%

Overview: Genes and Variation Evolution occurs due to the change of the relative frequency of alleles in a population over time. The alleles in an organism do not change during the organism’s lifetime.

Evolution Versus Genetic Equilibrium If a population is not evolving, the population is in genetic equilibrium. (Allele frequencies are not changing) Hardy–Weinberg principle Population should remain constant if all 5 conditions are met: 1. Large population 2. Random mating 3. No natural selection 4. No immigration/emigration 5. No mutations

Hardy–Weinberg Principle and In words, this is stated: (frequency of AA) + (frequency of Aa) + (frequency of aa) = 100% and (frequency of A) + (frequency of a) = 100% If p = 0. 40 and q = 0. 60: 48% 36% Probability of genotype aa: AA: 16%

Hardy–Weinberg Principle And Try this: Population of quackers Dominant: B = dark feathers Recessive: b = light feathers In a population of 50 ducks, 10 were light and 40 were dark. (Frequency of homozygous recessive organisms - bb)= q 2 = ____ (Frequency of recessive allele - b) q = _______ (Frequency of dominant allele - B) p = _______ (Frequency of homozygous dominant organisms - BB) p 2 = ______ (Frequency of heterozygous organisms - Bb) 2 pq =____