AP Biology Big Idea 1 Evolution Adapted from

AP Biology Big Idea #1 - Evolution Adapted from Rebecca Rehder Wingerden ©

Simply put… • Evolution is simply a change in the genetic makeup of a population over time.

Natural Selection is a major mechanism of evolution a. According to Darwin’s theory of natural selection, competition for limited resources results in differential survival. - Individuals with more favorable traits are more likely to survive and produce more offspring, - Thus passing traits to subsequent generations (Descent With Modification). “I think” Darwin’s 1837 sketch

Natural Selection is a major mechanism of evolution b. Evolutionary fitness is measured by reproductive success (aka: Darwinian Fitness). (c) Seed-eater (a) Cactus-eater (b) Insect-eater Beak Variation in Galapagos Finches

Natural Selection is a major mechanism of evolution c. Genetic variation and mutation play roles in natural selection. • A diverse gene pool is important for the survival of a species in a changing environment. Variation in a population

Natural Selection is a major mechanism of evolution d. Environments can be more or less stable or fluctuating, – and this affects evolutionary rate and direction; – different genetic variations can be selected in each generation.

Natural Selection is a major mechanism of evolution e. An adaptation is: – a genetic variation that is favored by selection and is manifested as a trait that provides an advantage to an organism in a particular environment. f. In addition to natural selection, chance and random events can influence the evolutionary process, especially for small populations. PBS Evolving Ideas - How Does Evolution Really Work? (7: 00 min. ) - http: //www. youtube. com/watch? v=xkw. RTIKXaxg Bozeman Biology: Natural Selection (11: 00 min. ) - http: //www. bozemanscience. com/001 -natural-selection

In the absence of evolutionary influence… a. …a population is said to be in Hardy-Weinberg equilibrium. • Conditions for a population or an allele to be in Hardy-Weinberg equilibrium are: - 1. A large population size (No Genetic Drift – Pop. Gen Sim) - 2. Absence of migration (No Gene Flow) - 3. No net Mutations - 4. Random mating (No Sexual Selection) - 5. Absence of environmental selection (No Natural Selection) • These conditions are seldom met in real populations.

Hardy-Weinberg h. Mathematical approaches are used to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population. – The Hardy-Weinberg principle describes a population that is not evolving. – If a population does not meet the criteria of the Hardy. Weinberg principle, then it can be concluded that the population is evolving.

Hardy-Weinberg • By convention, IF there are only 2 alleles at a locus, p and q are used to represent their frequencies. - p = A, and q = a • The frequency of alleles in a population will add up to 1 (= 100%) – For example, p + q = 1 • If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then – p 2 + 2 pq + q 2 = 1 – where p 2 (AA) and q 2 (aa) represent the frequencies of the homozygous genotypes and 2 pq (Aa) represents the frequency of the heterozygous genotype.

Selecting alleles at random from a gene pool 1) The allele frequencies of the population are 0. 8 (80%) and 0. 2 (20%). Frequencies of alleles p = frequency of CR allele = 0. 8 CW allele = 0. 2 2) If all of these alleles could be placed in a large bin, 80% would be CR and 20% would be CW. Alleles in a population 3) Assuming mating is random, each time two gametes come together, there is an 80% chance the egg carries a CR allele and a 20% chance it carries a CW allele. Gametes produced Each egg: 80% chance 20% chance Each sperm: 80% chance 20% chance

Selecting alleles at random from a gene pool 80% CR ( p = 0. 8) 20% CW (q = 0. 2) Sperm If the gametes come together at random, then the genotype frequencies of this generation are in Hardy-Weinberg equilibrium: CR (80%) CW (20%) Egg CR (80%) CW (20%) 64% -p 2 CR CR Gametes for each generation are drawn at random from the gene pool of the previous generation. 16% -pq CR CW 4% -q 2 CW CW 64% CRCR / 32% CRCW / 4% CW CW Gametes of this generation: 64% CR + 16% CR = 80% CR = 0. 8 = p 4% CW + 16% CW = 20% CW = 0. 2 = q 64% CRCR / 32% CRCW / 4% CWCW plants With random mating, these gametes will result in the same mix of genotypes in the next generation

Applying the Hardy-Weinberg Principle • We can assume the locus that causes phenylketonuria (PKU) is in Hardy-Weinberg equilibrium given that: – The PKU gene mutation rate is low – Mate selection is random with respect to whether or not an individual is a carrier for the PKU allele! • PKU metabolic disorder resulting from homozygosity for a recessive allele: – left untreated leads to mental retardation – newborns are tested for PKU at birth – symptoms can be lessened with a phenylalanine-free diet

Applying the Hardy-Weinberg Principle • If the occurrence of PKU is 1 per 10, 000 births…what is the frequency of heterozygote carriers? • The frequency of the recessive PKU allele is: – q 2 = 0. 0001 – q = 0. 01 • The frequency of the normal allele is: – p = 1 – q = 1 – 0. 01 = 0. 99 • The frequency of heterozygous carriers is: – 2 pq = 2 x 0. 99 x 0. 01 = 0. 0198 – or approximately 2% of the U. S. population Bozeman Biology: Solving Hardy Weinberg Problems (11: 00 min. ) http: //www. bozemanscience. com/solving-hardy-weinberg-problems Bozeman Biology: Population Genetics and Evolution (6: 00 min. ) http: //www. bozemanscience. com/ap-bio-lab-8 -population-genetics-evolution Bozeman Biology: Microevolution (7: 00 min. ) http: //www. bozemanscience. com/microevolution