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Day 5: Causes of Microevolution

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1 Day 5: Causes of Microevolution
Genetic Drift- loss of variation (allele frequencies) due to a sudden environmental act that reduces the population Gene Flow – change in variation (allele frequencies) due to immigration or emigration, movement of individuals into or out of the population Mutation- introduction of a new allele that becomes established in the gene pool Natural Selection- differential reproductive success, due to environmental pressure on a favorable phenotype Non-Random mating -mate choice is no longer based on equal chance or opportunity. Mate choice has become selective and based on some characteristic

2 Day 5: HW equilibrium Evolution occurs at the population level, population is defined as a group of the same species that live in the same area and interbreed, producing fertile offspring. Hardy Weinberg equilibrium theory states that a population’s allele frequencies will remain unchanged generation after generation, no evolution, if the following 5 conditions are held constant: Mutations do not change gene pool Mating is random and each organism has equal opportunity No natural selection, no phenotype is more favorable Population is large and contains variation No gene flow (emigration, immigration in/out of population)

3 Day 5: The equation used to determine if a population’s allele frequency is changing, in other words is the population “evolving”? p2 + 2pq + q2 = 1 p = dominant allele q = recessive allele p2= Homozygous dominant genotype (AA) 2pq= Heterozygous genotype (Aa) q2= Homozygous recessive genotype (aa) Each letter represents the frequency of a particular allele in the population p+q=1

4 Day 5: using the equation
We can look at a population and identify specific traits or phenotypes. We can actually count the number of individuals with those specific traits. Ex. If there are 100 pigs 25 of them are black and 75 of them are pink, or 25% is black and 75% is pink. What if you knew the black allele was Dominant and the pink allele was Recessive. Could you determine which ones had which genotype?

5 Day 5: HW equilibrium problem
If B= Black skin and b= pink skin in a pig If 25% of the population were black and 75% were pink, how many of them are Homzygous recessive bb Homzygous dominant BB Heterzygous Bb Remember that p is the dominant allele and q is the recessive allele. What does bb, BB, and Bb look like? BB- black Bb- black bb- pink p2- black 2pq- black q2= pink Can we calculate q? yes if we know q then we can find p

6 Day 5: practice problems
q= 0.6 a.0.6, b. 0.4, c. AA=.16 and Aa= .48 1. A randomly mating population has an established frequency of 36% for organisms homozygous recessive for a given trait. What is the frequency of the recessive allele in the gene pool ? 2. You have sampled a population in which you know that the percentage of homozygous recessive genotypes (aa) is 36%. Calculate the following The frequency of the a allele The frequency of the A allele Frequency of AA and Aa

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