Question

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

Answer: 630

Step-by-step solution

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-).

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

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)

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

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

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