Module 8
1. Module 8
1.7. Page 5
Module 8—Populations, Individuals, and Gene Pools
Lesson Summary
In Lesson 1 you investigated the following focusing questions:
- How do biologists quantitatively describe the composition of a population’s gene pool?
- What are the five conditions of the Hardy-Weinberg principle that affect frequency of alleles in a population’s gene pool, resulting in microevolution?
- What happens when conditions of the Hardy-Weinberg principle are not met?
A gene pool is described by how common each allele is in the population. The term used is frequency, and it is calculated by counting the number of the recessive or dominant alleles in the gene pool and dividing that number by the total number of alleles. When calculating frequencies, it is important to remember that each individual in the population carries two alleles.
When gene pool allele frequencies remain the same over time, the population is in Hardy-Weinberg equilibrium. Conditions needed for HWE are
- a closed population
- a large population
- no net change in mutation rate
- random mating
- no natural selection
If these conditions aren’t met, allele frequencies will change and, by definition, the population will evolve. Therefore, the conditions for evolution are
- an open population (gene flow)
- a small population (genetic drift)
- change in mutation rate
- non-random mating
- natural selection
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
frequency: number/total
gene flow: movement of alleles into or out of a population by immigration or emigration
Hardy-Weinberg Equilibrium: a principle that states that allele frequencies in a population will remain the same over time as long as the population is large, there is no gene flow, natural selection is not occurring, there is no change in mutation rate, and no mate selection is occuring
If allele frequencies do change, it indicates that microevolution is occurring in the population.
microevolution: a change in the frequency of alleles in the gene pool that results in a change in the characteristics of the population; does not result in a new species
natural selection: the process by which organisms with heritable traits survive in a particular environment, passing on their successful traits to the next generation
Those selected have greater reproductive fitness that either increases fertility or decreases mortality.
population: organisms of a particular species in a particular place at a particular time