Concepts from Lecture 19

Concepts from Lecture 19 - Concepts from Lecture 19. Causes...

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Unformatted text preview: Concepts from Lecture 19. Causes of Microevolution and Hardy‐Weinberg Equilibrium The Modern Synthesis is the integration of Mendelian genetics (how alleles are passed down from parent to child) with Darwinian evolution and the concepts of many important theoretical population geneticists. Populations are really the smallest unit of evolution – selection acts on individuals but the populations are what evolve. What is a gene pool? All the gene loci in all the individuals in a population. What is a population? A collection of individuals that are capable of interbreeding and producing fertile offspring and geographically localized. (This geographical localization is intentionally vague as it depends on the species, population, and geography involved really – i.e. fish may have a large range so that the geographic range that encompasses the population is much larger than that of a snail population). We study the change in allele frequency in population to study evolutionary charge at the microevolution level. Genotype frequency – proportion of a genotype in the population Allele frequency – proportion of an allele in the population Allele frequencies and Genotype frequencies will NOT change if a population is in Hardy‐Weinberg equilibrium. Hardy‐Weinberg was developed independently by Godfrey Harold Hardy 1877‐1947 (UK) Wilhelm Weinberg 1862‐1937 (Germany) The main equations that apply IF HW is met is that p2 + 2pq + q2 = 1 and p + q = 1 p = frequency of the common allele q = frequency of the more rare allele (but really it doesn’t matter which one is p or q) In the example from class (Slide 14). A population has A1 allele at 80% and and A2 allele at 20% then p (for A1) is 0.80 and q (for A2) is 0.20. A typical problem using these equation. If you are told what the frequency of a RECESSIVE disease is (i.e. Cystic Fibrosis) then you are being told the HOMOZYGOUS RECESSIVE GENOTYPE frequency. So if the disease is seen in 1 / 10,000 births. Then the frequency of homozygous recessive genotypes is 1/10,000 – so q2 = 1/ 10,000 or 0.0001. This means that q = square root ( 0.0001) = 0.01 If p + q = 1, then p = 1 – q = 0.99 If the question is – what is the expected frequency of CARRIERS we are asking what is the frequency of HETEROZYGOUS individuals. From the HW equation Heterozygous are 2pq. So to find this we just do 2 * 0.99 * 0.01 = 0.0198 or 1.98% of the population would be homozygous. And if you wanted to know how many people were homozygous for the dominant allele it would be = p2 or 0.99 * 0.99 = 0.98 or ~98% ...
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This note was uploaded on 08/15/2010 for the course BIO 5c taught by Professor Zhu/cardullo/rao during the Spring '08 term at UC Riverside.

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