Anthropology - 2.2.10.rtf

2.2.10 n = 50 Type M (Genotype MM) = 12 Type MN (Genotype MN) = 26 Type N (Genotype NN) = 12 EXPECTED: f(MM) = p^2 = .5^2 = .25 f(MN) = 2pq = 2(.5)(.5) = .50 f(NN) = q^2 = .5^2 = .25 OBSERVED; f(MM) = 12/50 = .24 f(MN) = 26/50 = .52 f(NN) = 12/50 = .24 This population is an equilibrium because the Observations match the Expectations. n = 50 Type M (MM) = 10 Type MN (MN) = 10 Type N (NN) = 30 1. Fine p and q, the allele frequencies of M and N. p: f(M) = 20+10/2x50 = 30/100 = 0.3 (total number of M alleles over total number of alleles) q: f(N) = 60+10/100 = 70/100 = 0.7 (total number of N alleles over total number of alleles) 2. Find the Observed and Expected EXPECTED: F(MM) = p^2 = .3^2 = .09 F(MN) = 2pq = 2(.3)(.7) = .42 F(NN) = q^2 = .7^2 = .49 OBSERVED: f(MM) = 10/50 = .20 f(MN) = 10/50 = .20 f(NN) = 30/50 = .60 This population is NOT an equilibrium. The expected is not matching the observed. M and N are co-dominant. We know this because there is a heterozygous MN. If you have co-dominant alleles, you will have 3 different genotypes and 3 different phenotypes. With a dominant/recessive system, there are 2 phenotypes and 3 genotypes. Forces of Evolution 1. Mutation - Any mistake in the genetic code. - Some things cause mutations to occur at higher frequency than the background rates. - Mutagens - environmental factors that increase the likelihood of mutations - Radiation, Carcinogens, Pollution. - Two major kinds of mutations: - Chromosomal Mutations - read about in book. Example - Down's Syndrome - Point Mutations - Affect a single base (ATGC) in the DNA or RNA. - Frame Shift Mutations - Addition: An extra base is added. - Deletion: A base is taken away. - Deleterious - a bad mutation - Substitution Mutations - GGA = Proline - CTC = Glutamic Acid - if the T is replaced with A, the codon no longer codes for Glutamic Acid, it codes for Valine. - In the beta chain, Glutamic Acid is the 6th codon. Since it is not, it causes Sickle Cell Anemia. - If CTC is changed to CTG, it is still Glutamic Acid. This is the Idea of Redundancy. Some amino acids are coded for by multiple codons. This helps prevent some genetic mistakes. This mutation has no effect - it is neutral. - Good mutations are called advantageous. - Neither Chromosomal or Point are "worse" than the other - they differ. 2. Genetic Drift - Evolutionary Change due to chance; random. - Whether or not genetic drift will have an impact on gene frequencies has to do with one aspect of the population: its size. - Size is the key for genetic drift. - Larger the population, the less of an effect of drift. - Smaller the population, the more of an effect of drift. - Living in cities is a recent development. For a long time, we lived in small groups. Drift had a large impact on our evolution. - Impact of Drift in small and large populations (examples) - If n = 100,000; f(T) = .8; f(t) = .2 - If 2 t people randomly die, n = 99,998; f(T) = 160,000/199,996 = .80001; f(t) = 39,996/199,996 = .19999 - In this large population, this random event does not have a big impact. - But, if n = 4; f(T) = 7/8 = .875; f(t) = .125 - The result of drift is that you lose genetic variation. - Founder's Effect - Original inhabitants in a new population can have skewed numbers and different numbers than the parent population. 3. Gene Flow