The incidence of Down syndrome, also known as trisomy 21, increases with increasing maternal age. Which of the following errors most likely produces this condition? A. Nondisjunction during meiosis II in either the male and female gameteB. Nondisjunction during either meiosis I or II in the female gameteC. Nondisjunction during either meiosis I or II in the male gameteD. Nondisjunction during meiosis I in either the male and female gamete

Answer:. Nondisjunction during meiosis I in either the male and female gamete

The failure of homologous chromosome to separate at mitosis, or failure of sister chromatids to separate at Anaphase of meiosis I or ii is called non-disjunction.

In this cell division anomaly the unsegregated chromosomes are separated into cells as single chromosomes, therefore extra copies are therefore inherited. This result is one of the cell having an extra copies of chromosomes than others (chromosomes 21.

If this extra chromosome copies is segregated into a sperm or egg, the resulting zygote cells will have extra copy as chromosome 21, and hence Down syndrome.

→It is more common in Meiosis 1 than ii, because of longer duration of the first stage of division than meiosis ii, given rooms to errors.

→Most common in women (with age increase) than men because of exchange of telomeres in them, which worsen with age. Their Meiotic mechanism which weaken with age, and more prone to errors compare to men,