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Biology 1201A Lecture 12: Lecture-12-Notes

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10 Dec 2015

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Western University

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Document Summary

Meanings of gene pool, genotype frequencies, allele frequencies, genetic equilibrium. Gene pool: sum of all the alleles at all gene loci in all individuals in a. Genotype frequency: % of individuals in a population possessing a population. particular genotype. allele frequency: abundance of one allele relative to others at the same gene locus in individuals of a population. Genetic equilibrium: point at which neither the allele frequency nor the genotype frequencies change in succeeding generations. How to calculate allele frequencies, given observed genotype frequencies. How to calculate genotype frequencies expected under genetic equilibrium let p equal one allele, q equal another allele equation that predicts genotype frequencies in offspring generation: (p+q)x(p+q)=p^2+2pq+q^2 if population is at genetic equilibrium, p^2 is predicted frequency for. Identify populations that are, or are not, at genetic equilibrium, given observed genotype frequencies. If populations genotype frequencies do not match predictions of null model, evolution is occurring and population is not at genetic equilibrium.

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Related Questions

Part A

Consider a population of wildflowers in which the frequency of the red allele C^Ris p = 0.7.

What is the frequency of the white allele (C^W) in this population?

Part B

This Punnett square shows allele combinations for all possible genetic crosses in the wildflower population described in Part A.

	C^R p = 0.7	C^W q = 0.3
C^R p = 0.7	C^RC^R ?	C^RC^W ?
C^W q = 0.3	C^RC^W ?	C^WC^W ?

What are the expected genotype frequencies in the offspring generation?

What are the expected genotype frequencies in the offspring generation?

0.49 C^RC^R(red flowers), 0.42 C^RC^W(pink flowers), 0.09 C^WC^W(white flowers)

0.49 C^RC^R(red flowers), 0.21 C^RC^W(pink flowers), 0.30 C^WC^W(white flowers)

0.09 C^RC^R(red flowers), 0.21 C^RC^W(pink flowers), 0.42 C^WC^W(white flowers)

0.09 C^RC^R(red flowers), 0.42 C^RC^W(pink flowers), 0.09 C^WC^W(white flowers)

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.