Module 8

1. Module 8

1.11. Page 4

Lesson 2

Module 8—Populations, Individuals and Gene Pools

Lesson Summary

This lesson focused on the following question:

What factors cause changes in the diversity of gene pool composition?

Gene pools are said to be changing when the frequency of the dominant and recessive alleles are changing. Another term meaning “gene pool change” is microevolution. Microevolution will occur if any of the following are taking place in the population:

genetic drift: chance changes in allele frequencies due to small populations

Genetic drift typically decreases variation in a population. The founder effect and bottleneck effects are examples of genetic drift.
natural selection: Organisms with certain phenotypes/genotypes have a selective advantage over others in a particular environment. Natural selection typically decreases diversity, especially in very competitive environments because one phenotype is much more successful and produces more young, passing on the favoured allele(s). Heterozygotes typically have the same advantage as the homozygous dominant genotype, unless there is a heterozygote advantage.
change in mutation rates: a change in allele frequencies caused by a greater rate of mutation from one allele to the other

Changes in mutation rates typically decrease variation in a population. Mutations resulting in new alleles will increase variation.
non-random mating (mate selection): choosing mates based on their phenotypes

These observable traits are usually displayed for prospective mates during formal courtship rituals. As a result, one allele is preferred over the other, which, after mating, translates to an increase in that allele in the offspring produced from that mating. Mate selection typically reduces variation in a population.
gene flow: Immigration and emigration increase diversity within populations, but decrease diversity/variation between populations.

If one allele becomes heavily favoured over the other, then there is a loss of variation in the population. In general, the more variation there is in a population gene pool, the better the population’s chances of surviving when environmental conditions change. Without plenty of variation in the gene pool, rapid environmental change commonly results in extinction.

Lesson Glossary

Consult the glossary in the textbook for other definitions that you may need to complete your work.

bottleneck effect: a type of genetic drift similar to the founder effect; occurs when a natural disaster thins the population to a small group that happens to be unrepresentative of the original group

Allele frequencies of the two groups will be dissimilar.

fecundity: fertility

founder effect: a type of genetic drift that occurs when a small population that is not representative of the main population migrates away

Allele frequencies of the two groups will be dissimilar.

genetic drift: a change in allele frequencies caused by chance events in a small gene pool, such as inbreeding caused by isolation of a small non-representative group or a few non-breeding individuals (bachelors)

Founder effect and bottleneck effect are examples of genetic drift.

mate selection (non-random mating): the process of choosing mates based on the presence of certain traits or phenotypes and, thus, genotypes

Traits are usually displayed in some form of courtship ritual.

mortality: death; may be due to kill-off (predation) or die-off (disease, starvation, or exposure)