You are performing crosses between two mice that are both heterozygous (D1D2) fo

Question

You are performing crosses between two mice that are both heterozygous (D1D2) for a mutation in the centromere region. Assume that the D1 allele is found in 90% of eggs produced by heterozygous females, but that sperm produced by heterozygous males exhibit the normal 1:1 ratio of D1 to D2 genotypes.

a. Which of Mendels rules is violated by the pattern of transmission exhibited by heterozygous females? Briefly explain why.

b. What genotypic segregation ratio will this monohybrid cross produce? Show your calculations but no written explanation is necessary.

c. Explain why it is biologically reasonable to imagine that a mutation in the centromere would alter the genotype ratios in oogenesis but not in spermatogenesis.

Explanation / Answer

a.. law of segregation. According the law of segregation all factors (in this case D1 and D2) segregate equally at the time of meiosis. But here it has not happened and D1 and D2 have been found in the ratio 9:1

b.. 9 (D1D1) :10 (D1D2) :1 (D2D2) ratio will be found instead of 1:2:1

c.. This is because in oogenesis only one one egg is formed from one parent, while in spermatogenesis 4 sperms are formed from one parent spermatogonia.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.