Mechanisms of Evolution Concept 4: Analyzing the evolution of populations through Hardy-Weinberg (microevolution) Chapter 23 in Campbell, pg in Holtzclaw

Goal: To analyze how populations change over time

The Evolution of Populations You must know: How mutation and sexual reproduction each produce genetic variation The conditions for Hardy-Weinberg Equilibrium How to use the Hardy-Weinberg equation to calculate allelic frequencies, to test whether a population is evolving.

Genetic Variation Crossing Over Independent Assortment Fertilization Gene pool = a population’s genetic make-up

Remember... Homozygous... (dominant) (recessive) Heterozygous... (dominant will “show”)

Preservation of Genetic Variation Diploidy – “hiding” recessive alleles Heterozygote advantage Ex) sickle cell anemia - malaria

What alters allele frequencies? Three major factors: 1. Natural Selection – causes adaptive evolution 2. Genetic Drift Founder Effect Bottleneck Effect 3. Gene Flow (Mutations also alter allele frequencies, but rare)

Natural Selection – causes adaptive evolution Relative Fitness Fitness compared to other members of the population… (your contribution to the gene pool of the next generation!) Three ways natural selection can work: Directional selection Disruptive selection Stabilizing selection

Try This! In what sense is natural selection more “predictable” than genetic drift?

Try This! In what sense is natural selection more “predictable” than genetic drift? Natural Selection: Alters allele frequency in a nonrandom way Tends to increase the frequency of alleles that increase an organism’s fitness and decrease the frequency of alleles that decrease an organism’s fitness Genetic Drift: Alters allele frequency by chance alone

Introducing… The Hardy-Weinberg Principle! Clarifies the factors that alter allele frequency A non-evolving population is in Hardy- Weinberg equilibrium.

Conditions for Hardy-Weinberg Equilibrium: No mutations Random mating No natural selection Extremely large population size (no genetic drift) No gene flow

The Hardy-Weinberg Formula p 2 + 2pq + q 2 = 1 where p + q = 1 See Handout...

Try This! In a certain population of 1000 fruit flies, 910 have red eyes while the remainder have sepia eyes. The sepia eye trait is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color? Hint: The first step is always to calculate q 2 ! Start by determining the number of fruit flies that are homozygous recessive…

Try This! Answer: You should expect 490 to be homozygous dominant. Calculations: q 2 for this population is 90/1000 = 0.09 q = = 0.3 p = 1 - q = = 0.7 The homozygous dominant frequency = p 2 = (0.7)(0.7) = Therefore, you can expect 49% of 1000, or 490 individuals, to be homozygous dominant.

Now… Handout!

The Evolution of Populations Do you know? How mutation and sexual reproduction each produce genetic variation The conditions for Hardy-Weinberg Equilibrium How to use the Hardy-Weinberg equation to calculate allelic frequencies, to test whether a population is evolving.