Population Genetics Studies the genetic variations within a population Characters left: 1000 Preview or Show next comments | View all 0 comments

Variations When different species members have differences in characteristics Ex. Dogs – one species but many varieties

Gene pool All of the genes in a population

Why does the dominant trait take over? Hardy and Weinberg stated the genes in a population will remain stable if under certain conditions

Assumptions of Hardy Weinberg There are no mutations. No genes transferred (No immigration or emigration) Mating is random. The population should be large. No selection is occurring

Hardy-Weinberg theorem An equation used to identify a non-evolving population. Looks at the frequency of each allele HARDY WEINBERG EQUILIBRIUM = There is no change in gene frequency in a population p2 + 2 pq + q2= 1

Mendel genetics – Apply to alleles in one gametes of one pair Mate two individuals heterozygous (Bb) for a trait. 25% offspring are homozygous for the dominant allele (BB) 50% are heterozygous like their parents (Bb) and 25% are homozygous for the recessive allele (bb) and express the recessive phenotype

populations have random alleles The frequency of two alleles in an entire population of organisms is unlikely to be exactly the same. Ex. population of hamsters: A) 80% of all the gametes in the population carry a dominant allele for black coat (B) and B) 20% carry the recessive allele for gray coat (b).

hamsters MENDEL monohybrid cross Results of random union of the two gametes produced by two individuals, each heterozygous for a given trait. As a result of meiosis, half the gametes produced by each parent with carry allele B; the other half allele b.   RANDOM POP Results of random union of the gametes produced by an entire population with a gene pool containing 80% B and 20% b. 0.5 B 0.5 b 0.8 B 0.2 b 0.25 BB 0.25 Bb 0.64 BB 0.16 Bb 0.25 bb 0.04 bb

Allele frequency P = frequency of dominant allele q = frequency of recessive allele Brown eyes vs blue eyes Brown (B) = P Blue (b) = q

Total frequency of alleles in population = 1 THEREFORE p + q = 1 (dom + res = 1) q =1 – p (res = 1 – dom) p = 1 – q (dom = 1 – res) Ex. R = red r = white there are 20% white flowers in a field q freq =.2 (20%) white then p freq = 1 - .2 = .8 (80%) red

Allele frequency of a dominant and recessive trait Similar to punnett square

Ex. Frequency alleles of Red (R) and white (r) flowers p2 + 2 pq + q2 = 1 Frequency freq freq of RR of Rr rr genotype genotype genotype

p2 + 2 pq + q2 = 1 Given: 4% of the population = white flowers (rr) What is the frequency of r? (q) What is the frequency of R? (p) What % of pop. = Rr? q2 = .04 so q = .2 so p = .8 4% rr 2(.8)(.2) = .32 Rr = 32% Rr 64% RR

NOT Hardy Weinberg equilibrium Change of allele frequency in 3 generations

5 agents of evolutionary change Things that CHANGE equilibrium of gene pool

1) Mutation Change in DNA code Mutagen

Mutations The origin of new alleles

2) Gene Flow Migration – Individuals move from one population to next Bring genes into new population

3) Non-Random Mating Self fertilization Inter breeding

4) Genetic drift A change in frequency due to chance

Bottleneck effect Genetic drift due to a reduction in population size Ex skittles

Tsunami bottle neck

Founder effect Genetic drift due to formation of a new colony with organisms with distinctly different phenotypes

5) Natural selection Darwin’s idea Survival of the fittest The environment influences who passes on their DNA

Fitness - ability to pass on traits to offspring The individuals in a population that are most fit are the ones that survive Attract mates better Catch prey better Hide better from predators

Polymorphism – When there are two or more forms of one character aids natural selection by increasing possible phenotypes

Geographic Variation Differences in gene pools between populations Can aid natural selection