BIO 102 Lecture Notes - Lecture 2: Allele Frequency, Genotype Frequency, Genetic Drift

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lemondinosaur366

2 Feb 2017

School

Quinnipiac University

Department

Biology

Course

BIO 102

Professor

Jack Kronengold

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Document Summary

Evolution is a property of populations not individuals. Different members of species may have slightly different nucleotide sequences - alleles. Specific alleles interact with the environment to influence the development of physical and behavioral traits. Gene pool - all of the alleles in all individuals of a population. Population genetics - the frequency, distribution and inheritance of alleles in populations. Diploid organisms (homologous chromosomes) contributes two alleles of each gene to the gene pool. Allele frequency - proportion of times a certain allele occurs in a population. Evolution = the change of allele frequency within a population. Population geneticist - defines evolution as the changes in allele frequencies that occur in a gene pool over time. Equilibrium population - a hypothetical population in which evolution does not occur. Under certain conditions allele and genotype frequencies in a population will remain constant no matter how many generations pass. Allele frequency doesn"t change as long as following conditions are met:

Related Questions

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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11.The evolutionary force of drift changes allele frequencies more quickly in which of the following kinds of populations?

a. large populations

b. small populations

10.Larger populations generate larger numbers of mutations.

True

False

9.Overdominance can result in changes in genotype frequencies, without changes in allele frequencies.

True

False

8.Protein coding genes usually evolve faster than pseudogenes.

True

False

7.Favorable mutations are not directly induced by environmenntal conditions where they increase fitness, instead they occur by chance, and if they happen to increase fitness, their frequency will increase in a population.

True

False

6.Consider a single gene with two alleles, A and a, in a population. What is the frequency of the Aa genotypes in zygotes drawn from a gene pool where A=0.3 and a=0.7, if they are in Hardy-Weinberg proportions?

1. 0.3

2. .09

3. 0.49

4. 0.42

5. 0.7

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. â¨

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. â¨

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 generationâ the offspring generationâand then let the parental generation âdieâ. â¨

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

Answer the questions that follow in Table 1. â¨

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? â¨

What happened to the frequency of the rare allele? â¨

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? â¨

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BIO 102 Lecture Notes - Lecture 2: Allele Frequency, Genotype Frequency, Genetic Drift

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