Groupings Species Orgs that may interbreed to produce fertile offspring Orgs that may interbreed to produce fertile offspringPopulation Local group of orgs of one species Local group of orgs of one species Evolution = change in the genetic makeup (allele frequencies) of a population Evolution = change in the genetic makeup (allele frequencies) of a population

Hardy-Weinberg Principle Allele frequencies are constant in a non-evolving population

Quantifying Evolution Gene Pool entire set of alleles present in the population entire set of alleles present in the populationEvolution change in frequency of alleles in the population change in frequency of alleles in the population p = frequency of one allele (usu. dom.) q = frequency of another allele (usu. Rec.) p + q = 1

Quantifying Evolution  p 2 = frequency of homozygous dominants  q 2 = frequency of homozygous recessives  2pq = frequency of heterozygotes p + q = 1 p 2 + 2pq + q 2 = 1

Hardy-Weinberg Probs  In pea plants, the allele for normal height is dominant over the allele for short height. In a pop of 1000, 490 are short. How many individuals would you expect to be homozygous dominant? Heterozygous? q 2 =.49 q 2 =.49 q=.7 q=.7 p=.3 p=.3 p 2 =.09 p 2 =.09 2pq=.42 2pq=.42

Hardy-Weinberg Probs  In the US, 64% of people have free earlobes. What is the frequency of the dominant allele? p 2 + 2pq=.64 p 2 + 2pq=.64 q 2 =.36 q 2 =.36 q=.6 q=.6 p=.4 p=.4

Hardy-Weinberg Conditions Hypothetical conditions that must exist in a population for no evolution to occur (allele frequencies constant)

Population Characteristics Hinder Evolution (Hardy-Weinberg Conditions)  Infinitely Large  Random Mating  Equal Survival  Isolation  No mutations Help Evolution (Natural Conditions)  Small  Genetic Drift Genetic DriftGenetic Drift  Natural Selection  Gene Flow Gene Flow Gene Flow  Mutations POPULATION SIZE MATE SELECTION VARIATION OF ADAPTIVENESS INTERACTION W/ OTHER POPS DNA CHANGES

Genetic Drift Random fluctuations in allele frequencies Example:  2 red, 2 blue orgs seek shelter  50% survive. All are red  Blues eliminated by chance (17%)  4 red, 4 blue head for shelter  50% survive. All are red  Blues eliminated by chance (1.4%)

Genetic Drift Bottleneck Effect Catastrophe cuts pop size Catastrophe cuts pop size  Decreased variety of traits  Altered allele frequencies  Genetic drift more likely  Founder Effect Small group emigrates to new habitat Small group emigrates to new habitat

Gene Flow  Introduction of new traits through immigration  May be beneficial or insignificant  New traits  altered trait frequencies 

Practice Within a population of butterflies, the color brown (B) is dominant over the color white (b). 4% of all butterflies are white. Calculate the following: a)The percentage of butterflies in the population that are heterozygous. b)The frequency of homozygous dominant individuals.

More Practice The allele for a hitchhiker's thumb is recessive compared to straight thumbs. In a population of 1000 individuals, 339 show the dominant phenotype. How many individuals would you expect for each of the three possible genotypes for this trait.