Bellwork  Define in your own words  Allele  Homozygous  Heterozygous  Recessive  Dominant

Hardy-Weinberg  If a population is not evolving, do you expect the genes (alleles) to change in a population in the next generation?

Hardy-Weinberg  If a population is not evolving, then gene frequencies should stay constant in a population from generation to generation. Parent generation Offspring

Why do scientists use Hardy-Weinberg  To determine if a population is evolving – scientists see if gene frequencies in populations reflect Hardy-Weinberg expectations, if not, than the population is evolving.

Criteria for Hardy-Weinberg  No Mutations  Random mating  No Selection  Extremely large population  No Gene Flow

Mutation  Rates are very low in nature  1-10 times per 100,000 cell divisions  Mutation is not common, but it is the source of variation and thus makes evolution possible

Nonrandom mating  Mating with individuals that live nearby or with related individuals  Does not change frequency of alleles, but increases the proportion of homozygotes in a population

Natural Selection  Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those that do not have such traits.  Ex. Sickle cell anemia and malaria

Natural Selection  Natural selection is the most powerful mechanism for genetic change  Natural selection acts on phenotypes not genotypes  Ex. Hemophilia expressed in homozygous recessive individuals, would only select against infected individuals not carriers  Usually, 1 recessive homozygous individual per 100, and 18 heterozygous per 100.

Polygenic trait  A trait that is influenced by several genes  Example: Human height and human skin color  Normal distribution

Types of selection  Directional selection  The frequency of a trait moves in one direction

Types of selection  Stabilizing selection  The distribution of a trait becomes narrower

Types of selection  Disruptive selection  When conditions favor individuals at both extremes of a phenotype

Large population size: If not, it can lead to genetic drift  Genetic Drift: The change in allele frequencies due to chance

Types of genetic drift  The Founder Effect – When few individuals become isolated from the larger population  Bottleneck Effect – A severe drop in population size because of a sudden change in the environment, so only a few survive (but not because they are more fit for their environment)

Gene Flow  The movement of individuals from one population to another, which may cause genetic change.

Using Hardy-Weinberg Equation p 2 + 2pq + p 2 = 1  Think of all alleles being in a “pool”  If the frequency of allele “p” is.8 and “q” is.2  What percentage of the population are heterozygous  2pq = 2(.8)(.2) = 32%

Using Hardy-Weinberg Equation p 2 + 2pq + p 2 = 1  Think of all alleles being in a “pool”  If the frequency of allele “p” is.8 and “q” is.2  What percentage of the population are homozygous dominant (p)  p 2 =.8 2 = 64%

Using Hardy-Weinberg Equation p 2 + 2pq + p 2 = 1  Think of all alleles being in a “pool”  If the frequency of allele “p” is.8 and “q” is.2  What percentage of the population are homozygous recessive (q)  q 2 =.2 2 = 4%

 If 4% are homozygous recessive, 64% are homozygous dominant and 32% are heterozygous, then…  4% + 64% + 32% = 100%