Microevolution

1. A change in allele frequency Microevolution

2. Q: How do scientists know when this occurs? • A: They compare it to a non-changing population • = Ideal population (like a “perfect” car… it only exists in a showroom)

3. 5 Characteristics of an “Ideal Population” • Population is very large • Large depends on the population, but thousands or hundreds are assumed • Mating is random • No phenotype has a greater chance of mating

4. No mutation of alleles • No immigration or emigration • No movement into or out of population • No selection occurs • No survival advantage goes to one phenotype over another

5. If these 5 conditions are met… • There is no change in allele/genotypic frequencies… • and no evolution • When these rules are broken, microevolution is said to be occurring.

6. For Hardy-Weinberg Equilibrium: • p stands for the frequency of the dominant allele Ex. “A” • q stands for the frequency of the recessive allele. Ex. “a” • In H-W, or 100% of the alleles

7. p2 = frequency of homozygous dominant genotype Ex. “AA” • q2 = frequency of homozygous recessive genotype Ex. “aa” • 2pq = frequency of heterozygous genotype Ex. “Aa” 

8. Example 1: • Approximately 9% of Americans of African descent suffer from sickle cell anemia, which is inherited as a recessive trait. • What is the frequency of the sickle cell allele? • Approximately what percentage of this sub-population carries the sickle cell allele?

9. Example 2: • Cystic fibrosis is known to occur as a recessive trait in human populations. In a genetic study, the frequency of the recessive allele for a population was found to be 2.0%. • What percentage of the population would be expected to exhibit Cystic Fibrosis? • What percentage of the population would be normal, but carry a CF allele?