BIOB51H3 Lecture Notes - Lecture 9: Allele Frequency, Genotype Frequency, Genetic Drift

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cyanmarten183

10 Mar 2020

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Hardy-weinberg assumptions: allele frequencies of a population will not change if, population is infinitely large, genotypes do not confer differences in fitness, there is no mutation, mating is random, there is no migration. If these conditions are met, you get the hardy-weinberg equilibrium. Predictions from hardy-weinberg: allele frequencies can be used to predict genotype frequencies p2+2pq+q2. =1: p = the frequency of one allele at a locus, q = the frequency of the other allele at the same locus, hence, p + q = 1. Key concepts ii: hardy weinberg serves as the fundamental null model in population genetics, hardy weinberg is useful because it provides mathematical proof that evolution will not occur in the absence of selection, drift, migration, or mutation. Biob51- evolutionary ecology: mutation: the main source of genetic variation, migration: movement of alleles between populations, drift: chance disappearance of alleles.

Related Questions

How can evolutionary biologists use Hardy-Weinberg equilibrium while studying populations of organisms that they suspect may be evolving?

a Scientists can tell a population is evolving if the allele frequencies change.

b Scientists can tell a population is evolving if the genotype frequencies are constant.

c Scientists can tell a population is evolving if the frequencies of homozygous dominant and homozygous recessive individuals are not equal.

d Scientists can tell a population is evolving if the frequencies of homozygous dominant and homozygous recessive individuals are equal.

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Consider a single locus with three alleles: A₁, A₂, and A₃.

1) Write down all of the diploid genotypes possible at this locus.

2) Derive the equation for the frequency of allele A₁ as a function of the genotype frequencies.

Consider the following two datasets:

At the M locus:

In a study of 1000 adults, the following genotype numbers were found:

M₁M₁ - 213 individuals

M₁M₂ - 489 individuals

M₂M₂ - 298 individuals

At the S locus:

In a study of 4555 adults, the following genotype numbers were found:

S₁S₁ - 3564 individuals

S₁S₂ - 979 individuals

S₂S₂ - 12 individuals

Assignment: For both loci

Calculate the frequency of the alleles.

Calculate expected number of each genotype if the population were in Hardy-Weinberg equilibrium.

Identify which locus most clearly violates at least one of the H-W assumptions

Q1. What are alleles?Different forms of the same gene.Different genes.The different characteristics of an organism.Genes found only in humans.Q2. If you add up the frequency of homozygotes + the frequency of heterozygotes for one gene (i.e. at one locus) in a population, what number do you get?Q3. People who are heterozygous for the sickle-cell allele:Are susceptible to malaria but not sickle-cell anemia.Are susceptible to sickle-cell anemia but not malaria.Are not susceptible to either sickle-cell anemia or malaria.Are susceptible to both sickle-cecell anemia and malaria.Q4. In the case study in this lab, which genotype is represented by "2pq" in the Hardy-Weinberg equation?Homozygous HbAHomozygous HbSHeterozygous HbA/HbSNo specific genotypeQ5. Suppose that, in an isolated village, the proportion of individuals that have sickle-cell anemia is 0.1 (or 1 of every 10 people). What proportion of the population should be sickle-cell carriers, according to Hardy-Weinberg expectations?Q6. When you simulated the elimination of malaria at the beginning of the lab, once the allele frequencies stabilized, what was the frequency of the HbA allele?Q7. When you investigated regional differences, what was the frequency (over many generations) of the HbS allele in the village in the "slightly wet" part of Africa?Q8. What is the number of deaths due to sickle-cell anemia in a region without mosquitoes expected to be?Very lowVery highModerateRelated to the frequency of malaria allelesQ9. As long as there are multiple alleles of a gene in a population, why will the frequencies of the alleles always change over time?Because natural selection changes all allele frequencies in populations over time.Because genetic drift causes random fluctuations of allele frequencies in populations.Because diseases will eliminate some of the alleles, generating fluctuations in their frequencies.Because allele frequencies fluctuate before the alleles eventually become fixed.Q10. Imagine a huge population with a gene that has ten functionally equivalent, neutral alleles. A small but genetically representative group of individuals from the big population is transported to an island, forming a small population. Which of the statements below best describes what will likely happen over time, and why?Because natural selection doesn't act on neutral alleles, the frequencies in the two populations should remain the same over time.Genetic drift will cause one allele to first become fixed in the island population, and later to become fixed in the original, large population.Genetic drift will result in the allele frequencies of the two populations diverging over time, with alleles being lost sooner in the island population.The allele frequencies of the two populations will change similarly due to a combination of genetic drift natural selection.

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BIOB51H3 Lecture Notes - Lecture 9: Allele Frequency, Genotype Frequency, Genetic Drift

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