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Chapter 7: Problem 17

Three loci, mitochondrial malate dehydrogenase that forms \(a\) and \(b(M D H a, M D H b),\) glucouronidase that forms 1 and \(2(G U S 1\) \(G U S 2\) ), and a histone gene that forms \(+\) and \(-(H+, H-),\) are located on chromosome \(\\# 7\) in humans. Assume that the \(M D H\) locus is at position \(35, G U S\) at position \(45,\) and \(H\) at position 75 A female whose mother was homozygous for \(M D H a, G U S 2,\) and \(H+\) and whose father was homozygous for \(M D H b, G U S 1,\) and \(H-\) produces a sample of 1000 egg cells. Give the genotypes and expected numbers of the various types of cells she would produce. Assume no chromosomal interference.

Short Answer

Expert verified
Answer: 630

Step by step solution

01

Determine the parental genotypes

The mother is homozygous for MDHa, GUS2, and H+, and the father is homozygous for MDHb, GUS1, and H-. Thus, the mother's genotype is (MDHa MDHa, GUS2 GUS2, H+ H+) and the father's genotype is (MDHb MDHb, GUS1 GUS1, H- H-).
02

Calculate recombination frequencies

The recombination frequency is calculated according to the map distance: recombination frequency = map distance / 100. Given the map distances of the loci, we have: - MDH - GUS: (45 - 35) / 100 = 0.1 - GUS - H: (75 - 45) / 100 = 0.3 - MDH - H: (75 - 35) / 100 = 0.4
03

Determine possible gametes

The female can produce four possible gametes based on the recombination frequencies: 1. MDHa GUS2 H+ (no crossover) 2. MDHa GUS2 H- (crossover between GUS and H) 3. MDHa GUS1 H+ (crossover between MDH and GUS) 4. MDHa GUS1 H- (double crossover)
04

Calculate the probabilities of each gamete

Using the recombination frequencies calculated in Step 2, we can now determine the probabilities of each gamete being produced: 1. Probability(MDHa GUS2 H+) = (1 - 0.1)(1 - 0.3) = 0.63 2. Probability(MDHa GUS2 H-) = (1 - 0.1)(0.3) = 0.27 3. Probability(MDHa GUS1 H+) = (0.1)(1 - 0.3) = 0.07 4. Probability(MDHa GUS1 H-) = (0.1)(0.3) = 0.03
05

Calculate the expected number of each type of egg cell

The female produces a total of 1000 egg cells, so we can now calculate the expected number of each type of egg cell based on the probabilities in Step 4: 1. Expected number of MDHa GUS2 H+ cells = 0.63 * 1000 = 630 2. Expected number of MDHa GUS2 H- cells = 0.27 * 1000 = 270 3. Expected number of MDHa GUS1 H+ cells = 0.07 * 1000 = 70 4. Expected number of MDHa GUS1 H- cells = 0.03 * 1000 = 30
06

Final answer:

The female is expected to produce the following types and numbers of egg cells: 1. 630 MDHa GUS2 H+ cells 2. 270 MDHa GUS2 H- cells 3. 70 MDHa GUS1 H+ cells 4. 30 MDHa GUS1 H- cells

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Most popular questions from this chapter

What three essential criteria must be met in order to execute a successful mapping cross?

In Drosophila, a cross was made between females expressing the three X-linked recessive traits, scute bristles \((s c),\) sable body \((s)\) and vermilion eyes ( \(v\) ), and wild-type males. All females were wild type in the \(\mathrm{F}_{1}\), while all males expressed all three mutant traits. The cross was carried to the \(\mathrm{F}_{2}\) generation and 1000 offspring were counted, with the results shown in the following table. No determination of sex was made in the \(\mathrm{F}_{2}\) data. (a) Using proper nomenclature, determine the genotypes of the \(\mathrm{P}_{1}\) and \(F_{1}\) parents. (b) Determine the sequence of the three genes and the map distance between them. (c) Are there more or fewer double crossovers than expected? (d) Calculate the coefficient of coincidence; does this represent positive or negative interference?

Explain the meaning of the term interference.

Review the Chapter Concepts list on page \(136 .\) Most of these center on the process of crossing over between linked genes. Write a short essay that discusses how crossing over can be detected and how the resultant data provide the basis of chromosome mapping.

In a series of two-point map crosses involving five genes located on chromosome II in Drosophila, the following recombinant \((\sin -\) gle- crossover) frequencies were observed:$$\begin{array}{lr} p r-a d p & 29 \\ p r-v g & 13 \\ p r-c & 21 \\ p r-b & 6 \\ a d p-b & 35 \\ a d p-c & 8 \\ a d p-v g & 16 \\ v g-b & 19 \\ v g-c & 8 \\ c-b & 27 \end{array}$$ (a) If the adp gene is present near the end of chromosome II (locus 83 ), construct a map of these genes. (b) In another set of experiments, a sixth gene ( \(d\) ) was tested against \(b\) and \(p r,\) and the results were \(d-b=17 \%\) and \(d-p r=23 \% .\) Predict the results of two-point maps between \(d\) and \(c, d\) and \(v g,\) and \(d\) and \(a d p\)
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