1. Evolution of populations Ch 21

2. I. Background  Individuals do not adapt or evolve  Populations adapt and evolve  Microevolution = change in allele frequencies in a population  Requires inherited traits : genetic variability

3. II Sources of Genetic Variation  A. mutation….only gamete mutations passed on  1. point mutation : sickle cell anemia  2. may be silent….no Δ amino acid  3. may be neutral…. No change in phenotype  a. introns  b. amino acid Δ makes no difference  4. may be beneficial or detrimental  5. may be lethal

4.  B. Chromosomal Changes – change many loci  1. duplication of genes (cross over error)  2. transposable elements  a. transposons just move  b. retrotransposons leave a copy at original position and move = more copies of gene  3. large changes often harmful, but a few extra copies often good  4. extra copy can take on new function

5.  C. Sexual Reproduction  1. crossing over  2. independent assortment  3. fertilization 2 n possible zygote chromosome combinations   D. rapid reproduction = higher rate of mutation

6. III. Hardy-Weinberg Principle  A. detects microevolution of particular genes  1. determines what gene frequencies would be if there were NO evolution (null hypothesis)  2. compare null hypothesis with data collected from population  3. null hypothesis supported = no evolution  4. data differs from null hypothesis = evolution

7.  B. Based on Population Gene Pools  1. population = all individuals of a species in an area that reproduce together  2. gene pool = all copies of every allele at every locus in all individuals of a population  3. if all alleles of a gene are the same in the gene pool the gene is said to be fixed  4. frequency of that gene would be 100% 

8.  C. Genotype Frequencies  1. If you know the genotypes…..  2. And there are 500 individuals in population  3. # individuals/ total population = % of population with that genotype

9.  D. Allele Frequencies (ƒ)  1. Number of dominant alleles =  a. # homozygous dominant x2 plus  b. # heterozygous  2. total frequency =  100%  p = dominant alleleƒ  q = recessive alleleƒ  p + q = 1 (100%) 

10.  E. Null Hypothesis : no evolution  1. frequencies of alleles will remain constant from generation to generation determined only by segregation and recombination of alleles  2. so in next generation each allele is equally likely to join with any other allele in offspring  3. mating must be completely random and all allele combinations must survive equally well  4. so we use multiplication rule of probability to predict % of genotypes of offspring

11.  F. Rule of Multiplication (probability 11.9)  1. A is 80% of gene pool so each egg has 80% chance to get an A  2. sperm has same 80% chance so.. Chance of AA indiv. =.8 x.8 or p x p = p 2

12.  3. a is 20% of gene pool so each egg has 20% chance to get an a  4. sperm has same 20% chance so.. Chance of aa indiv. =.2 x.2 or q x q = q 2

13.  5. The remainder of population is heterozygous  6. There are 2 ways for a zygote to get one of each allele  Egg A & sperm a = .8 x.2 (p x q)  Egg a & sperm A = .2 x.8 (q x p)  So heterozygotes =  2(.2 x.8) or  2pq

14.  G. Hardy-Weinberg Formula =  p 2 + 2pq + q 2 = 1  p 2 = frequency of homo dominant  q 2 = frequency of homo recessive  2pq = frequency of hetero  1 = 100 % of population

15.  H. conditions for Hardy-Weinberg Equilibrium  1. no mutations  2. random mating  3. no natural selection  4. extremely large population  5. no gene flow into/out of population  a. immigration  b. emigration

16. IV. Causes of Evolution  A. Natural Selection  1. Differential fitness of one allele  2. example  a. 0% of fruit flies had DDT resistance in 1930  b. 37% had allele for resistance in 1960  c. null hypothesis rejected  d. explanation : natural selection favored files with DDT resistance allele.

17.  B. Genetic Drift : Chance events cause random change in allele frequency  1. Small population size maximizes effect  a. may decrease genetic variation & fix alleles  2. Founder Effect  a. new population started by few individuals  b. fewer alleles, different % s than main pop.  3. Bottleneck Effect  a. Population nearly wiped out  b. few remaining ind. have limited gene pool  c. population may recover but genetic variation only recovers very slowly with out immigration

18. Florida Panther separate subspecies for 100 years  Population dropped to under 50 in 1970  Inbreeding increased incidence of disorders  kinked tail 88%, but only 27% in other pop.

19. Desert Bighorn Sheep  Island population of desert bighorn sheep  20 founders in 1975 650 in 1999  Genetic variation significantly less than mainland

20.  C. Gene Flow  1. alleles move into or out of population  2. individuals move  a. emigration – out  b. immigration – in  3. gametes move  4. increases genetic diversity  5. makes populations more similar

21. Big horn sexual selection  http://www.youtube.com/watch?v=E6Fx3CaJhg k http://www.youtube.com/watch?v=E6Fx3CaJhg k