1. Population Genetics
Chapter 4

2. Population Genetics
The study of biological populations and the changes in genetic composition
Involves the examination and modelling of changes in the frequencies of traits in populations
Individual organisms do not evolve, populations do
Largest reproductive population is the species
Speciation - the formation of a new, distinct species

3. Evolution and Variation
From a modern genetic perspective, we define evolution as a change in allele frequency from one generation to the next
Allele frequency refers to the indicators of the genetic makeup of a population, the members of which share a common gene pool, or the sum of alleles carried by the population
Factors that produce and redistribute variation:
Mutation
Gene Flow
Genetic Drift and Founder Effect
Recombination

4. Evolutionary Change
Certain conditions must be assumed for a population to remain in genetic equilibrium:
Mutation must not be taking place
The population must be infinitely large
Individuals from neighboring populations must not introduce new alleles
Mating must take place at random
Natural selection must not be occurring

5. Mutation Mutation is a molecular alteration in genetic material:
Is always random
Must occur in a gamete to effect evolution
Rates for any given trait are usually low
When combined with natural selection, evolutionary changes can occur and can occur more rapidly
Only way to produce new genes
Can occur due to mistakes in DNA replication, exposure to chemicals, temperature fluctuations, exposure to radiation, etc.

6. Gene Flow The exchange of genes between populations.
If individuals move temporarily and mate in the new population (leaving a genetic contribution), they don’t necessarily stay there
Consistent feature of human evolution
Example: The offspring of U.S. soldiers and Vietnamese women represent gene flow, even though the fathers returned to their native population

7. Genetic Drift
Genetic drift occurs solely because the population is small:
Alleles with low frequencies may not be passed to offspring and eventually disappear from the population
Population Bottleneck
Reduction in the size of a population due to environmental events
One cause of genetic drift

8. Founder Effect
Occurs when a small band of “founders” leaves its parent group and forms a colony elsewhere
A new population is established and as long as mates are chosen within this population, all the members will be descended from the founders
A once rare allele that was carried by even one of the founders can eventually become common

9. Recombination
The production of offspring with combinations of traits that differ from those found in either parent
Leads to a novel set of genetic results
Doesn’t change allele frequencies, or cause evolution
Changes the composition of parts of chromosomes
Affects how some genes act, and slight changes of gene function can become material for natural selection to act upon

10. Genetic Equilibrium Punctuated Equilibrium Genetic Equilibrium
Evolution marked by periods of rapid change and/or speciation, set between long periods of little or no change
Genetic Equilibrium
Evolution can be defined as a change in the gene pool of a population
If not evolving, these frequencies remain constant
The calculation for genetic equilibrium is known as Hardy-Weinberg equilibrium
The formula is: p2+2pq+q2=1
p = frequency of dominant alleles
q = frequency of recessive alleles

11. Hardy-Weinberg Formula
Genetic equilibrium is only a hypothetical state
Populations are always evolving
The Hardy-Weinberg Formula can be used to measure the strength of evolutionary forces by making comparisons between the hypothetic situation of no change and the observed situations of change
The formula can be used to test hypotheses about evolutionary change and also to measure the increase, decrease, of static situation in regard to specific genetic conditions including genetic diseases

12. Non-random Mating
The equilibrium model assumes that individuals in the population are mating at random
A consanguineous mating is a mating between relatives
May have a significant effect on rare alleles
Another example of nonrandom mating would be assortive mating
Similar mates reproduce with one another more frequently

13. Differential Fertility
Genetic equilibrium assumes that all mating is equally fertile, but this is obviously not the case
Differential fertility and mortality are both examples of natural selection, the heart of evolutionary theory
Factors that result in greater fertility will be passed on to the next generation with higher frequency
Conditions that result in decreased fertility or higher mortality will tend to be eliminated