Evolution of Populations

A Introduction

1. What is a population?

2.  The "Gene Pool"

"Courtesy of Windows to the Universe, http://www.windows.ucar.edu"

B. Genotype, phenotype and allele frequencies can be calculated

- genotype frequency:

example 1000 individuals

- phenotype frequency:

- allele frequency:

Calculate genotype frequencies in the population using a Punnet Square:

0.7 A and 0.3 a (male population) 

                      X

0.7 A and 0.3 a (female population)                                                                          

- Hardy-Weinberg Equation:

p = frequency of dominant allele (A)

q = frequency of recessive allele (a)

p  + q = 1

p² + 2pq + q² = 1

(AA) + (Aa) + (aa)

What is the frequencies of each of these genotypes when A = 0.7 and a = 0.3?

C. Hardy-Weinberg Equilibrium

Gene Frequencies of a population will not change if the following requirements are met:

Random mating,  No net mutations,  Large Population Size (no genetic drift),  No migration (no gene flow),  No natural selection

Evidence from research:

1. Non-random mating

-mating tends to occur with close neighbors (inbreeding)

-inbreeding does not change overall allele frequency in population, but can increase frequency of homozygous individuals and reduce fitness

2. Mutation (Read textbook to refresh your memory about this topic)

-What is a mutation?

somatic

sex cell

3. Genetic Drift

a. What is it?

In a population of 10,000 how many individuals would carry a rare allele with a q= 0.1?

What about in a population of 10?

b. Bottleneck Effect

c. Founder Effect

4. Migration or Gene Flow

a. The New Face of America

5. Natural Selection

a. Natural selection leads to adaptive change: it is not random

b. Genetic variation is the "raw material" for natural selection

-natural selection acts on the phenotype

structural

biochemical

behavioral

-expression of the phenotype is complex involving both the genotype and the environment:

single gene------single trait (Mendelian)

single gene------many traits (Pleiotropy)

many genes------one trait (polygenic)

-discrete characters: single gene locus with different alleles

-quantitative characters: polygenic with character distributed in a particular pattern (Normal distribution)

c. Sexual reproduction contributes to variation

d. Sex and natural selection

-sexual dimorphism leads to competition among males for females

-sex selection data in guppies

e. Genetic polymorphism is common in populations

-enzymes

f. Maintenance of genetic variation

-diploidy allows recessive alleles to be 'hidden' from selection

-heterozygote advantage

g Modes of natural selection

Evidence for natural selection is based on changes in distribution of phenotypes in the population

-stabilizing

from: http://www.micro.utexas.edu/courses/levin/bio304/popgen/nat.selection.html

-directional

cactus:

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/C21_Directional.html

-disruptive

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/C21_Disruptive.html