Question

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 1

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,

Explanation: