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Biology 1001A Chapter Notes - Chapter 18: Genotype Frequency, Allele Frequency, Genetic Drift

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pinkserval403
27 Jan 2020
School
Western University
Department
Biology
Course
Biology 1001A
Professor
Tom Haffie

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Document Summary

In observational experiments there is no control so experimenters use a null model: hardy-weinberg principle: the conditions under which a population of diploid organisms achieves genetic equilibrium, 1. The population is closed to migration from other populations: 3. The population is infinite in size (there is no genetic drift: 4. All genotypes in the population survive and reproduce equally well (selection is not acting on the trait being considered: 5. Individuals in the population mate randomly with respect to the trait being considered.

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Related Questions

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.

Hemoglobin and Fitness Instructions Directions: Neutral Evolution

1. Obtain 20 beans of two different colors (e.g., white and red). Count out 16 white and 4 red beans. The white beans represent the Hn allele and the red beans represent the Hs allele. This is the genetic makeup of your starting population. (Note: You can use any objects that can readily be categorized into two groups, such as coins, colored rocks, or paper clips.)

2.Calculate the frequency of both alleles [f(Hn) and f(Hs)] and record them in Table 1. In our experiment frequency is a measure of how many copies of a given allele exist in the gene pool (i.e., a proportion). Use decimal values. 


3.Arrange the beans into pairs. These pairs represent the genotype of each of 10 individuals in the population. Record the number of individuals with each genotype [f(Hn Hn), f(Hn Hs), and f(HsHs)] in Table 1. 


4.Now imagine that the individuals are living and reproducing with each individual reproducing at the same rate (i.e., all individuals produce two copies of each of their alleles into the next generation). Obtain enough beans to represent the next generation— the offspring generation—and then let the parental generation “die”. 


5.Calculate the frequency of each allele in the offspring generation and record it in Table 1. 


Answer the questions that follow in Table 1. 


Table 1

f(HnHn) f(HnHs) f(HsHs) f(Hn) f(Hs)
oiginal generation
offspring generation

Answer the following questions to help you understand the exercise:

What happened to the frequency of the common allele? 


What happened to the frequency of the rare allele? 


What happened to the frequency of the common and rare alleles when the starting frequencies were different from yours

What happens to allele frequencies from one generation to the next if there are no evolutionary forces acting on the population?