Module 8

Module 8—Populations, Individuals, and Gene Pools

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Describing Gene Pools

When people are interested in the genetic composition of a population, they are interested in its gene pool. Consider a population of only ten field mice on the southern Alberta prairies. Assume that mice have two different alleles for coat colour, brown (B) and white (b). The genotypes for the mice are shown in the diagram below.

Imagine that each mouse can throw its two alleles for coat colour into a basket—this is the gene pool of the population.

The gene pool can be described in three ways:

• by its genotype frequencies
• by its phenotype frequencies
• by its allele frequencies

Frequency is measured by dividing the number of a particular subgroup by the total group. The symbol f indicates frequency. The following examples show how to calculate genotype, phenotype, and allele frequency in the population for these field mice.

Note: The shorthand f(BB) will be used to replace the long-hand "frequency of the BB genotype.”

Note: The shorthand f(Black) will be used to replace the long-hand “frequency of the brown phenotype.”

Note: The shorthand f(B) will be used to replace the long-hand “frequency of the B allele.” Remember that there are ten individuals, so there are 20 alleles in total.

For population geneticists, the most useful way to describe a gene pool is by its allele frequencies. Do you know why?

Self-Check 

SC 1. In a population of ten mice, suppose three have the homozygous dominant genotoype, two are heterozygotes, and five have the homozygous recessive genotoype. What is the frequency of each genotype in the population? What is the frequency of the dominant and recessive alleles?