Maternal nondisjunction, the failure of homologous chromosomes or sister chromatids to separate properly, is associated Down syndrome and other types of aneuploidy in humans. Maternal age is associated with nondisjunction, although no age effect is seen in males. How might these findings be explained with respect to gametogenesis?

Answer and explanation:

Gametogenesis is a process in which gametes are formed from germ cells through meiosis. The genetic content of germ cells will be reduced from diploid (2n) to haploid (n). This means that the normal number of chromosomes of the species will be reduced by half.

This process in men takes place in the testicles and its purpose is to produce sperm. In the case of women, it occurs in the ovaries and the result is the production of oocytes.

Gametogenesis is performed in two successive chromosomal and cytoplasmic divisions, which are called meiosis I and meiosis II. In meiosis I the homologous pairs are joined and then separated by the mitotic bone, distributed at the poles of the cell. Then, in meiosis II, the sister chromatids of each chromosome are going to separate and are distributed in the new cells. Between both meiosis there is no division of DNA, for this reason it is that the chromosomal number is divided in half. Both meiosis include prophase, metaphase, anaphase and telophase.

As the failure to properly separate homologous chromosomes or sister chromatids is associated with Down syndrome, we can infer that it has to do with failures that occur in meiosis that will give rise to gametes.

An important difference is that gametogenesis in men occurs throughout life so they will always have "new" spermatozoa, instead, in women the gametes begin their meiosis during the prenatal stage, the oocytes will remain at rest and continue the process in each menstrual cycle from puberty (a group of oocytes is activated in each cycle and meiosis continues, being able to be fertilized or not). That is, women are born with all the oocytes they will have during their entire life. Thus, as the cycles pass the oocytes will be increasingly old and will have more risks of suffering problems during the separation of chromosomes in meiosis.