1. Populations, Gene Pools, & Microevolution
Chapter 13

2. What you need to know!
How mutation and sexual reproduction each produce genetic variation.
The conditions for Hardy-Weinberg Equilibrium.
How to use the Hardy-Weinberg equation to calculate allelic frequencies and to test whether a population is evolving.

3. Evolution & Gene Pools A single organism does not evolve
One animal has the genes it was born with and they do not change
Populations evolve
Populations are multiple animals of a single species (that can interbreed)
All the genes/alleles in a population are called a gene pool
Microevolution is the change of a species’ relative frequencies of alleles

4. Relative Frequencies
The number of times alleles appear in a gene pool divided by the total number of alleles
What are the Relative Frequencies of fur color for these mice?
Relative Frequency: Brown: 30/50, Black: 20/50
Sample Population
Frequency of Alleles
allele for brown fur
allele for black fur
48% heterozygous black
16% homozygous black
36% homozygous brown

5. Sources of Microevolution
Natural Selection: differential reproductive success of certain phenotypes lead to a(n) increase/decrease of certain alleles
Mutation: introduces new alleles
Gene flow: add or remove alleles to a gene pool based on migration

6. Sources of Microevolution
Genetic Drift: Random change of allele frequency in small populations
Founder Effect: spike in gene change due to genetic drift after a small population inhabits a new region
Bottleneck effect: a small surviving group (near extinction) gives rise to a new population with a dramatically different gene pool

7. Sources of Microevolution
Sexual Selection: choosing mates based on heritable characteristics
Sexual dimorphism: differences between males and females of the species
Distance: Mating more often occurs between close neighbors than distant neighbors
Inbreeding: reproduction with close relatives in small populations

8. Genetic Equilibrium
In 1908, 2 mathematicians (Hardy & Weinberg) stated that the allelic frequency in a given population accounts for changes in populations
They developed the concept of genetic equilibrium: how alleles in a population stay constant from one generation to another (no evolution)

9. Equilibrium Requires No natural selection No mutations No gene flow
No genetic drift
Random mating