1. Diversity of Individuals and Evolution of Populations
Chapter 23
Diversity of Individuals and
Evolution of Populations 1

2. I. Evolution occurs with the gradual change in the allele frequency within a population over time
a population of one species has a variety of individuals
for any feature, there can be many phenotypes
phenotypes are determined by alleles
must examine change in allele frequency of a population over time

3. II. Examining population’s allele and genotype frequency to study evolution
population - localized group of individuals of the same species
species - a group of populations that can interbreed
gene pool - all alleles for all genes present in a population
genetic structure of a population - population frequency of alleles & genotypes

4. III. Hardy-Weiberg theorem for a non-evolving population - a look at population structure
Assume a gene with 2 alleles: A and a
allele frequency is: A (0.8 = 80%) and a (0.2 = 20%)
chance of AA offspring = x = 0.64**
chance of aa offspring = x = 0.04**
chance of Aa offspring = (0.8 x 0.2) x 2 = 0.32 **
** this would be expected genotype structure at equilibrium (Hardy-Weinberg equlibrium)

5. Assume a gene with 2 alleles: A and a
frequency of allele #1 (eg. A = 0.8) = p
frequency of allele #2 (eg. a = 0.2) = q
chance of resulting in AA = p x p = p2
chance of resulting in aa = q x q = q2
chance of resulting in Aa = 2 (p x q) = 2 p q
p p q q2 = 1
allows us to calculate population structure

6. IV. Evolution is - a generation-to-generation change in a population’s frequency of alleles and genotypes
change in the Hardy-Weinberg frequency over time is a sign that some alleles can result in a phenotype which gives a “selective” advantage over other alleles
for Hardy-Weinberg equilibrium to be maintained:
large population size must exist
no gene flow from other populations can occur
no net mutations can occur
random mating must be happening
no natural selection can be occurring

7. V. Deviations from Hardy-Weinberg can result from:
genetic drift (population size)
gene flow
mutation results in new alleles
non-random mating (assortive mating, inbreeding)
natural selection (differential success of offspring)

8. VI. Natural selection is dependent upon variation - alleles that give rise to a variety of phenotypes
most phenotypes are the result of multiple genes
polymorphism - variation of a certain item for discussion
sources of polymorphism:
genetic mutation - results in new and different alleles
recombination - results new combinations of alleles

9. VII. Fitness - the relative contribution of an individual to the population gene pool
Think about what is meant by the following:
gene, allele, genotype, phenotype
species
population
natural selection
allele and genotype structure of a population
evolution