Question

Primary spermatocytes are diploid (2n) cells with all of the organelles typically found in eukaryotic animal cells. A representation of spermatogenesis from a primary spermatocyte with six chromosomes is shown in Figure 1. Figure 1. A representation of spermatogenesis Primary Spermatocyte Meiosis Secondary Spermatocytes Meiosis II Spermatids Spermatozoa (a) Describe the process in meiosis that ensures that both maternal and paternal chromosomes are passed on to each spermatozoon.

Answer 1

Primary spermatocyte = Diploid cell
i.e. it is the meiocyte = The cell that undergoes meiosis to produce haploid gametes

a. The primary spermatocyte contains two sets of chromosomes i.e. one maternal set and one paternal set
These chromosomes are randomly aligned at the equatorial plate during meiotic-metaphase-I.
Random arrangement of these chromosomes ensures that each daughter cell acquires a combination of paternal and maternal chromosomes.
This phenomenon is referred to as 'Independent assortment'

b. Crossing-over between non-sister chromatids of homologous pair generates recombinant chromosomes i.e. maternal and paternal genomes are mixed to create recombinant chromosomes.

c. Disjunction = Proper separation of chromosomes during cell division
Nondisjunction = Improper separation of chromosomes during cell division
6 chromosomes in primary spermatocyte = 4 chromosomes in one cell + 2 chromosomes in one cell
This could be due to nondisjunction during meiotic anaphase-I

d. Mitochondrial genes are inherited from mother to progeny.
Most of the mitochondria in the zygote are maternally derived.