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Chapter 5: Problem 18

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 \(-\left(H^{+},\right.\) \(\left.H^{-}\right),\) 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: The expected number of cells in a sample of 1000 egg cells are: - 30 cells with MDHa GUS1 H+ genotype - 70 cells with MDHa GUS1 H- genotype - 270 cells with MDHa GUS2 H+ genotype - 630 cells with MDHa GUS2 H- genotype

Step by step solution

01

Calculate recombination probabilities

To calculate recombination probabilities, find the difference between the given positions of the loci and divide by 100. Recombination probability between MDH and GUS is (45 - 35) / 100 = 0.1, and between GUS and H is (75 - 45) / 100 = 0.3.
02

Determine parental gametes

The mother has genotype MDHa MDHa GUS2 GUS2 H+ H+ and the father has genotype MDHb MDHb GUS1 GUS1 H- H-. The combination of these parental genotypes could produce the following four gametes: 1. MDHa GUS1 H+ 2. MDHa GUS1 H- 3. MDHa GUS2 H+ 4. MDHa GUS2 H-
03

Calculate expected number of cells for each type

Using the probabilities from Step 1 and the four possible gametes from Step 2, we can calculate the expected number of cells for each type in a sample of 1000 egg cells: 1. MDHa GUS1 H+: 0.1 * 0.3 * 1000 = 30 cells 2. MDHa GUS1 H-: 0.1 * 0.7 * 1000 = 70 cells 3. MDHa GUS2 H+: 0.9 * 0.3 * 1000 = 270 cells 4. MDHa GUS2 H-: 0.9 * 0.7 * 1000 = 630 cells So, in the sample of 1000 egg cells, the expected number of cells with each genotype are: - 30 cells with MDHa GUS1 H+ genotype - 70 cells with MDHa GUS1 H- genotype - 270 cells with MDHa GUS2 H+ genotype - 630 cells with MDHa GUS2 H- genotype

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Most popular questions from this chapter

In this chapter, we focused on linkage, chromosomal mapping, and many associated phenomena. In the process, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions? (a) How was it established experimentally that the frequency of recombination (crossing over) between two genes is related to the distance between them along the chromosome? (b) How do we know that specific genes are linked on a single chromosome, in contrast to being located on separate chromosomes? (c) How do we know that crossing over results from a physi- cal exchange between chromatids? (d) How do we know that sister chromatids undergo recombination during mitosis? (e) When designed matings cannot be conducted in an organism (for example, in humans), how do we learn that genes are linked, and how do we map them?

List some of the differences between a linkage map obtained by analyzing crossovers and a physical map obtained by sequencing the DNA.

The gene controlling the Xg blood group alleles \(\left(X g^{+} \text {and } X g^{-}\right)\) and the gene controlling a newly described form of inherited recessive muscle weakness called episodic muscle weakness \((E M W X)\) (Ryan et al., 1999 ) are closely linked on the X chromosome in humans at position \(\mathrm{Xp} 22.3\) (the tip of the short arm \() .\) A male with EMWX who is \(\mathrm{Xg}^{-}\) marries a woman who is \(\mathrm{Xg}^{+}\), and they have eight daughters and one son, all of whom are normal for muscle function, the male being \(\mathrm{Xg}^{+}\) and all the daughters being heterozygous at both the \(E M W X\) and \(X g\) loci. Following is a table that lists three of the daughters with the phenotypes of their husbands and children. (a) Create a pedigree that represents all data stated above and in the following table. (b) For each of the offspring, indicate whether or not a crossover was required to produce the phenotypes that are given.

Why are double-crossover events expected less frequently than single-crossover events?

Are mitotic recombinations and sister chromatid exchanges effective in producing genetic variability in an individual? in the offspring of individuals?
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