22- Mary is SsMm, and these two genes are located on the same chromosome. Allele

Question

22- Mary is SsMm, and these two genes are located on the same chromosome. Alleles ‘M’ and ‘S’ are her paternal copies. During prophase I crossing over occurred between the alleles of gene M, and the first polar body she produced this month carried ssMm (all the gene copies on the replicated cs). The gamete (egg cell) she produced this month would contain:   

A- SM only    B- sm only    C- Sm only    D- sM only    E- SM or Sm     F- sm or sM     G- sm or SM or Sm or sM

8- Genes B and D are located on the same chromosome. Mark is “BbDd” and the sperm that made him was Bd. A crossing over occurs at locus B of one of his primary spermatocytes (this means a crossing over occurs between two non-sister chromatids, and as a result, the B and b alleles of this chromosome are exchanged). How many copies of allele B would be present in each of the resulting secondary spermatocyte in prophase II?   

A- One     B- Two    C- Four    D- both A and B are possible

15- Gene A is X-linked. How many copies of gene A do exist in the primary spermatocyte of Mark in G1?   

A- One with any genotype    B- Two with any genotype    C- One only if Mark is A-, and zero if Mark is a-    D- Two only if Mark is A-    E- Two only if Mark is a-    F- None if Mark is a-    G- two of the above could be the answer

Explanation / Answer

1) SM or Sm - If after crossing over, the alleles carried by the first polar body is ssMm, then the ooocytes will carry the remaining alleles that is SM or Sm. Since, the first polar body and the secondary oocyte will contain only one member of each original chromosome pair.

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