Evolution of Populations Genes & Variation--What causes Genetic Variation in Populations?

Mutations Gene Shuffling Crossing Over

Gene Pools and Allele Frequencies What is a gene pool? (All of the genes and information from all members of a particular species) What are Allele Frequencies? (How many times that allele occurs in the gene pool---eg. Black fur B = 40%)

Sources of Genetic Variation Mutations Gene Shuffling -- 23 chromosomes can produce 8.4 million different combinations of genes Crossing Over -- Further, “Shufffles the deck” Producing more combinations

New Combinations of Alleles

Single Genes & Polygenic Traits Single Gene Traits AA, Aa, aa Polygenic Traits AABBCC, AaBbCc (3 Genes)-------->

Natural Selection on Single gene Traits Can Lead to changes in the Allele Frequencies and consequently----> Evolution Example--Black and brown lizards Red (mutation) doesn’t survive as well on a dark background

Natural Selection on Polygenic traits Can affect the distributions of phenotypes in 3 ways--- 1) Directional selection 2) Stabilizing selection 3) disruptive selection

Stabilizing Selection -->Selects for the average form

Directional Selection -->Selects for an extreme

Diversifying Selection--Selects for both extremes

Natural Selection on Single Gene Traits

Genetic Drift

Genetic Drift in The Amish

Example of Genetic Drift An example is the frequency of total color-blindness among the inhabitants of Pingelap, an island in Micronesia. In approximately 1775, a typhoon reduced the population of the island to only 20. Among survivors, one of them was heterozygous for achromatopsia.

After few generations, the prevalence of achromatopsia is 5% of population and 30% as carriers (by comparison, in the United States, only 0.003% of the population has complete achromatopsia.

Amish polydactyl (6 fingered) Achondroplastic Dwarf

Evolution vs. Genetic Equilibrium Evolution = Genetic Change What does Genetic Equilibrium = ? NO CHANGE ! POPULATIONS WOULD STAY THE SAME, “IN EQUILIBRIUM”

Remember the Blue-footed Booby?

Hardy-Weinberg Equilibrium

Conditions for Equilibrium (Hardy--Weinberg) What would the conditions have to be for no change? ie. No Evolution 1. No mutation 2. No natural selection 3. Large population 4. All members of the population breed

5. Random mating 6. everyone produces the same number of offspring 7. no migration in or out of the population

Speciation

Isolating Mechanisms GEOGRAPHIC REPRODUCTIVE BEHAVIORAL TEMPORAL

GEOGRAPHIC ISOLATION Leads to--> Reproductive Isolation

REPRODUCTIVE ISOLATION Species can no longer reproduce with the, “New” species Eg. 2 species of fruitflies Guava or Banana? The evolution of different mating location, mating time, or mating rituals:

TEMPORAL ISOLATION Mating at different times of the year Other frogs-- Green frogs--> April Bullfrogs--> June

BEHAVIORAL ISOLATION Courtship rituals--(Dances, Flashes,) Food preferences

Firefly--> Flashes

Misconception: “Natural selection gives organisms what they ‘need.’ ”