Evolution of Populations Population- group of individuals of the same species that live in the same area and interbreed. Gene Pool- populations genetic makeup Allele Frequency- how common is an allele in a population

Evolution of Populations Genetic Variation- differences among individuals in the composition of their genes or other DNA sequences 1.Mutations – change in the nucleotide sequence of an organism’s DNA 2.Sexual Reproduction- allows for the unique combination of alleles that each individual receives from its parents

Evolution of populations Evolution = change in allele frequencies in a population hypothetical: what conditions would cause allele frequencies to not change? non-evolving population REMOVE all agents of evolutionary change 1.very large population size (no genetic drift) 2.no migration (no gene flow in or out) 3.no mutation (no genetic change) 4.random mating (no sexual selection) 5.no natural selection (everyone is equally fit)

Hardy-Weinberg equilibrium Hypothetical, non-evolving population preserves allele frequencies Serves as a model (null hypothesis) natural populations rarely in H-W equilibrium useful model to measure if forces are acting on a population measuring evolutionary change W. Weinberg physician G.H. Hardy mathematician

Hardy-Weinberg theorem Counting Alleles assume 2 alleles = B, b frequency of dominant allele (B) = p frequency of recessive allele (b) = q frequencies must add to 1 (100%), so: p + q = 1 bbBbBB

Hardy-Weinberg theorem Counting Individuals frequency of homozygous dominant: p x p = p 2 frequency of homozygous recessive: q x q = q 2 frequency of heterozygotes: (p x q) + (q x p) = 2pq frequencies of all individuals must add to 1 (100%), so: p 2 + 2pq + q 2 = 1 bbBbBB

H-W formulas Alleles:p + q = 1 Individuals:p 2 + 2pq + q 2 = 1 bbBbBB BbBbbb

What are the genotype frequencies? Using Hardy-Weinberg equation q 2 (bb): 16/100 = q (b): √.16 = p (B): = 0.6 q 2 (bb): 16/100 = q (b): √.16 = p (B): = 0.6 population: 100 cats 84 black, 16 white How many of each genotype? population: 100 cats 84 black, 16 white How many of each genotype? bbBbBB p 2 =.36 2pq=.48 q 2 =.16

Using Hardy-Weinberg equation bbBbBB p 2 =.36 2pq=.48 q 2 =.16 Assuming H-W equilibrium Sampled data bbBbBB p 2 =.74 2pq=.10 q 2 =.16 How do you explain the data? p 2 =.20 2pq=.64 q 2 =.16 How do you explain the data? Null hypothesis

1.You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: 1.The frequency of the "aa" genotype. 2.The frequency of the "a" allele. 3.The frequency of the "A" allele. 4.The frequencies of the genotypes "AA" and "Aa." 5.The frequencies of the two possible phenotypes if "A" is completely dominant over "a."

Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on an exam, calculate the following: The percentage of butterflies in the population that are heterozygous. The frequency of homozygous dominant individuals

1.Cystic fibrosis is a recessive condition that affects about 1 in 2,500 babies in the Caucasian population of the United States. Please calculate the following. 1.The frequency of the recessive allele in the population. 2.The frequency of the dominant allele in the population. 3.The percentage of heterozygous individuals (carriers) in the population.

Heterozygote Advantage In tropical Africa, where malaria is common: homozygous dominant (normal) die or reduced reproduction from malaria: H b H b homozygous recessive die or reduced reproduction from sickle cell anemia: H s H s heterozygote carriers are relatively free of both: H b H s survive & reproduce more, more common in population Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. Frequency of sickle cell allele & distribution of malaria

Other Ways Allele Frequencies Are Altered Natural selection can cause adaptive evolution. Some alleles are consistently favored over others. Allows organisms to have a better match with their environment. Genetic Drift- Chance events can cause an unpredictable fluctuation in allele frequencies. 1. Founder Effect- When a few individuals become isolated from a larger population.

2. The Bottleneck Effect- sudden change in environment can acuse a severe drop in population size. Summary of genetic drift Significant in small populations Can cause allele frequencies to change at random Can lead to a loss of genetic variation within population

Gene Flow- transfer of alleles in or out of a population due to movement of fertile organisms Reduces genetic difference Affects how well a population can adapt to local environment conditions Can improve or deter ability Plays a big role in human evolution

Adaptive Evolution Consistently caused by natural selection Relative fitness- contribution an individual makes to the gene pool of next generation relative to contribution of other individuals

Directional, Disruptive and Stabilizing Selection 1. Directional selection- conditions favor individual exhibiting one extreme of a phenotypic range, thereby shifting populations frequency curve

2. Disruptive selection- conditioned favor individuals at both extremes of phenotypic range.

3. Stabilizing selection- acts against both extreme phenotypes and favors intermediate