Population Genetics and Evolution Gene Pools Hardy-Weinberg 5 Fingers of Evolution

The bell curve Traits vary and can be mapped along a bell curve, which shows that most individuals have average traits, whereas a few individuals have extreme traits.

What causes phenotype variations? *Genetic variations cause variations in phenotypes How do variations come about within the same species? 1) Mutations in gametes form new alleles 2) Sexual reproduction -Crossing over in meiosis -Independent assortment -Fertilization

The Gene Pool Gene Pool – all of the alleles for every gene of a particular population

Allele Frequencies Allele frequency- how often an allele occurs in a populations gene. w W w w w w W w w w w w w w w w w w W w w w W w Calculate the Allele frequencies for W and w!

Genotype Frequencies Genotype Frequencies- the percent of the population that is homozygous dominant, heterozygous and homozygous recessive at any given time. Example: Population total: 2396 AA = 910 Aa=695 aa= 791 Calculate genotype frequencies…

Genotype Frequencies Dimples are dominant to no dimples. 20% of the population has no dimples. How many people of a population of 5437 are homozygous recessive?

Hardy-Weinberg Equilibrium It is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable. Allele frequencies and genotype frequencies do not change. 5 Conditions for Equilibrium 1) Large Population (no genetic drift) 2) Random mating 3) No mutations 4) No gene flow – no immigration or emigration 5) No natural selection If at least one of these conditions is NOT met, then the population is EVOLVING!

5 Causes of Evolution 1) Genetic drift occurs in small populations 2) Sexual selection occurs when certain traits increase an individual’s success at mating 3) Mutations- a change in DNA changes allele frequencies 4) Gene flow- genes move in and out of the population due to immigration and emigration 5) Natural Selection (3 types)…

Gene Flow Movement of fertile individuals between populations (immigration and emigration -Gain/lose alleles from one population -Reduce genetic differences between populations

Genetic Drift Genetic Drift 2 Types: Bottle neck-A random event such as a fire or flood that causes change. It kills individuals regardless of traits —any one can die or be lucky enough to survive Founder Effect- Individuals leave a large population to establish a new population. Only alleles that came with the founders will be passed on.

Polydactyly in Amish population Founder Effect A few individuals isolated from larger population Certain alleles under/over represented Polydactyly in Amish population

3 Types of Selection

The bell curve Traits vary and can be mapped along a bell curve, which shows that most individuals have average traits, whereas a few individuals have extreme traits.

Directional Selection Favors the formation of more-extreme traits.

Stabilizing Selection Favors the formation of average traits.

Disruptive Selection Favors extreme traits rather than average traits

Natural Selection Genetic Drift

Genetic Drift vs. Natural selection -A random event such as a fire or flood that causes change. It kills individuals regardless of traits —any one can die or be lucky enough to survive Natural selection -An prolonged or permanent change in the environment which causes individuals with certain traits to succeed and others to die

Big Ideas *Natural selection acts directly on phenotypes *Gene pools and allele frequencies change as a result of evolution