1. Generation to Generation in Allelic Or Genotypic Frequency

MICROEVOLUTION I. INTRODUCTION A. Evolution 1. Generation to generation in allelic or genotypic frequency a) Change in a population genetic structure (1) Only one loci needs to be changing for population evolution (2) No such thing as individual evolution II. GENETIC DRIFT A. Too small a population size 1. Sampling error a) 1000 coin tosses (500:500) b) 5 coin tosses (2:3 = 400:600) 2. Common in population under 100 individuals B. Example 1. Parent generation a) AA - Aa - aa b) A = 50%; a = 50% c) Perhaps the homozygous dominant individuals do not mate, therefore, the heterozygote and homozygous recessive only leave offspring 2. F1 generation a) Aa - Aa - aa - aa b) A = 25%; a = 75% C. Bottle neck effect 1. Unselective killing a) Earthquakes, fires, flooding, hunting 2. North American elephant seal a) Hunted to 20 b) Numbers up to 30,000 since protected c) Genes fixed at 20 loci examined 3. South American elephant seal a) Not hunted b) Multiple alleles at all loci examined D. Founder's effect 1. A few individuals colonize a new habitat a) Ponds, islands, etc. b) Even just one, if pregnant or with seed 2. Tristanda Cuhna (a British colony) a) Founded in 1814 by 15 persons (1) One carrier of the recessive allele for retinistis pigmentosis b) Population at 240 in 1960 (1) 4 showed trait and 9 were carriers III. GENE FLOW A. Perhaps pollen from white flower pollinates a population of red flowers 1. Might result in some pink flowers 2. Preference of pollinators for flower color will effect the fate of the white allele IV. MUTATIONS A. Original source of allelic variation B. Types 1. Neutral a) Fingerprints 2. Advantageous a) House fly and DDT b) Antibiotic resistance in bacteria c) Sickle cell anemia 3. Disadvantageous a) Phenylketonuria C. Not much by itself without selection V. NON-RANDOM MATING A. Types 1. Interbreeding / self fertilization 2. Assortive mating a) select partners like themselves B. Effect 1. Increases the number of homozygotes and decreases number of heterozygotes a) With random mating you might expect 1:2:1 ratio of genotypes, but with non- random mating you might get a 5:2:5 ratio b) AA x AA = AA + AA; aa x aa = aa + aa; Aa x Aa = AA + Aa + Aa + aa 2. Allelic frequency does not change, but genotypic frequency is altered a) Recessive phenotype is increased (1) Often defective, hence taboos against close marriages