15- Gene A is X-linked. How many copies of gene A do exist in the primary sperma

Question

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

20- Mary is SsMm, and these two genes are located on two different chromosomes. During prophase I crossing over occurred at both loci, and so, the alleles of both loci were exchanged. The first polar body she produced this month carried SsMm. 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

21. 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 at both loci (alleles of both loci were exchanged), 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

Explanation / Answer

15.
Mark = Male = XY
Primary spermatocyte = 2X
So, the primary spermatocyte contains one copy of A if he is A_ and zero copies if he is aa.
Option C is correct.

16.
Parent: SsMm
Gametes produced: SM Sm sM sm
Option G is correct.

17.
Parent: SsMm
These two genes are located on the chromosome. So, they do not assort independently.
Assumption: 1 chromosome contains SM and the other sm after crossing over.
Gametes produced: SM or sm
Option E is correct.

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