Microevolution Topic 8

Population: a group of individuals of a single species that live in the same area at the same time

What happens as a result of microevolution?

Some changes occur in phenotype are readily observed, like the change in the frequencies of brown/green beetles

Other important changes may be very subtle and hard to physically observe

Therefore, biologists frequently examine the alleles of genes within the organisms

What happens as a result of microevolution?

• Changes to phenotypes and genotypes

We can tell microevolution is taking place because of the changes in genotype and allele frequencies

For a given population, how can we tell if evolution is taking place?

How do you measure allele and genotype frequencies?

• gene pool: all the alleles of all the genes in a certain population

• genetic structure: allele frequency & allele distribution (genotype frequency) for a single gene

  • size of the population (N)

  • frequency of each genotype

  • frequency of each allele

What are actual allele & genotype frequencies?

Actual genotype frequency = (# of particular genotype)/ (population size)

Actual allele frequency = 2(#Homozyguous) + 1(Heterozyguous)/ 2(Populations size)

Example: Calculare actual genotype frequencies

AA 90/200 = 0.45

Aa 40/200 = 0.2

aa 70/200 =0.35

200 = N

2(200) =400

((90 ×2) +40)/400 =0.55 (allele frequency of A)

((2 × 70) +40)/ 400=0.45 (allele frequency of a)

Expectation if evolution is not occurring

If there are no mechanisms of microevolutions acting then..

• all individuals experience Equal Reproductive Success

• predicted genotypic rations are achieved in the next generation

• the frequency of alleles and

If evolution isn’t occurring, what does that mean?

Expected genetic structure

Define the allele frequencies as A = p and a = q

• males = f(A) = p, f(a) = q

• female gametes (fA) = p, f(AA) = p x p = p²

The Hardy-Weinberd Equation is a tool used to predict the expected allele frequencies in a population, given the allele frequencies

p²+ 2pq + q² = 1

Calculating expected allele frequencies

65/215 =0.302

Testing for evolution

Null hypothesis - there is no difference between the actual and the expected structure, therefore the population isn’t evolving

• requires comparison of actual numbers of individuals with each genotype compared to expected number of individuals

How to determine if a population is in HWE?

1. determine the actual (observed) allele frequencies

2. calculate expected genotype frequencies

3. May also need to determine expected genotype numbers

4. Do a statistical test known as the