Question

Primary spermatocytes are diploid (2n) cells with all of the organelles typically found in eukaryotic animal cells. Spermatogenesis begins with a primary spermatocyte with 6 chromosomes, which undergoes meiosis 1 to produce two secondary spermatocytes with 3 chromosomes in each. Each of the secondary spermatocytes undergoes meiosis 2 to produce 2 spermatids, with 3 chromosomes in each. The 4 spermatids mature into spermatozoa.
(a) Describe the process in meiosis that ensures that both maternal and paternal chromosomes are passed on to each spermatozoon.





(b) Explain why the genetic content of individual chromosomes in a spermatozoon most likely differs from the genetic content of individual chromosomes in a primary spermatocyte.





(c) In some instances, meiosis of a primary spermatocyte with six chromosomes results in two spermatozoa that contain four chromosomes and two spermatozoa that contain two chromosomes. Predict the most likely cause.

Answer 1

Answer: a. Genetic recombination (crossing over)

b. Can also be explained in terms of crossing over

c. Non disjunction of homologous chromosomes in meiosis 1

Explanation:

The process that allows for the transfer of both the paternal and maternal materials to is the crossing over process that takes at meiosis 1 changing them to secondary spermatocytes. While they are still primary spermatocytes, they are still diploid cells having both the maternal and paternal chromosomes. But since the spermatozoon is an haploid cell, it is able to retail some of both parents chromosome by the crossing over event which takes place between homologous paternal and maternal chromosomes allowing them to exchange materials. Thus the chromosomal contents of the primary spermatocyte differs from that of the spermatozoon.

C. This can occur as a result of the one of the homologous chromosome pair refusing to separate at meiosis 1 with one gamete containing 4 chromosomes/8 sister chromatids and the second having 2 chromosomes/4 sister chromatids.