BIS 2B Lecture Notes - Lecture 5: Allele Frequency, Zygosity, Round-Off Error

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31 Jul 2018

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From generation to generation within a population, the genotypes of offspring result from putting alleles together in pairs (because individuals are diploid). If there are only 2 alleles in a population (let"s call them a & a), these alleles can come together in 3 different genotypes: aa, aa or aa. The frequency of a particular genotype depends on the frequency of the alleles within it. The likelihood of getting a particular genotype depends on how likely the alleles are to meet each other. In other words, it all depends on the frequency (commonness or rarity) of each allele. Then, we can see that the likelihood of getting the genotype aa, that is a is contributed from the male, and a is contributed from the female (the genotype. Aa in the offspring) would be 30% once for the first allele and 30% again for the second allele. Mathematically, we say the f(aa) = 0. 3 x 0. 3 or f(aa) = (0. 3) 2.

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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¨

greyotter669

a) Lets think beyond the individual. A population of tortoises lives on the island of San Cristobal in the Galapagos islands.

Tortories are diploid.

There are 100 individuals on the island.

The gene responsible for shell shape is autosomal and has two forms: Rounded (R) or Saddleback(r).

The frequency of R in the population is 0.7; the frequency of r is 0.3

How many R copies of the gene are in the population?

b) Let us assume that all individuals have equal opportunity to mate and that alleles are equally distributed among males and femals.

Use the Punnet Square method ( or a modification of this) to calculate the expected frequency of each tortoise shell genotype in the next generation.

(HINT: Think of a coin flip as a punnett square, then think of a coin that is not "fair", meaning it is more likely to land on heads. how would you modify the ###s you use to calculate probabilities { which in this case are equal to expected frequencies}

I'm sorry for putting two questions on one request but I'mrunning out of uses for my subscription period. Please help!

1. Answer the following questions

(a âd) given the following information.

Please show your mathematical equations used and your work forfull credit, highlight your final answer:

Suppose we have one locus with two alleles with the followingabsolute viabilities

and initial allele frequencies.

Absolute viability:

AA = 0.95

AB = 0.95

BB = 0.65

Initial allele frequency:

Frequency A (p) = 0.2

Frequency of B (q) = 0.8

a. What are the relative fitnesses of the genotypes?

b. What is the average fitness in the population?

c. Assuming a general selection model what will the frequency ofboth alleles A and B be after one generation of selection?

d. What will the percent (%) change in the allele frequency of Abe after one generation of selection?

Will it be an increase or decrease change?

2. In wild Soay Sheep horn size is largely determined by asingle gene with two alleles. Let us assume for simplicity thatsheep with the dominant allele, H⁺, have large horns andsheep with recessive allele, H^s, have short horns. Belowis a table showing the relative reproductive success of individualswith the following genotypes. Assume relative reproductive successis our measure of relative fitness of genotypes.

Answer the following question (a-Âe).

Relative Reproductive Success:

H+H+ is 1

H+Hs is 1

HsHs is 0.60

a. What is the selection coefficient (s) value against therecessive allele (Hs)?

b. What type (mode) of selection is occurring at this locus ANDwhat is the relationship of the relative fitnesses of thegenotypes?

c. You want to model selection at this locus to determine therate at which the advantageous allele frequency will change afterselection. What is the proper equation to use to determine theallele (H+) frequency change after one generation of selection?

d. Assume before selection the initial allele frequencies areH+=0.1 and Hs=0.9. What will the change in H+ frequency be afterone generation of selection against the Hs allele? Show yourmathematical work and highlight your final answer.

e. Draw a predicted graph of the rate of change for H+AND Hs over say 600 generations. I am interested in if you can (a)label your axes correctly, (b) indicate the initial allelefrequencies correctly, and (c) show the predicted trendlines for the change in allele frequencies over generations.You should make one graph with two lines (one for H+ and one forHs). Label your lines as H+ and Hs, This eans you do notneed to perform any math to make your plots.)

burgundyyellowjacket390

BIS 2B Lecture Notes - Lecture 5: Allele Frequency, Zygosity, Round-Off Error

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