Question

1.    a- A child is born with anuelpoidy (XXX) for their sex chromosomes. Can you determine whether the non-disjunction event that resulted in this anueploidy occurred in the mother or the father?

1. b-If the anueploidy occurred in the father, would it have occurred during meiosis I or meiosis II?

**please Explain***

Answer 1

a.

The chromosomes are reduced to half of the original number of parents when they are passed on to offspring after meiosis. Sometimes, the chromosomes fail to separate properly and inherited with an extra copy. This phenomenon is called nondisjunction. The nondisjunction may occur in either Meiosis I or meiosis II.

Usually males have XY chromosomes and females have XX chromosomes. When nondisjunction occurs during mitosis or meiosis it may result in addition of an extra copy. In females, sex aneuploidy may be resulted with addition of an extra X chromosome. This is XXX condition rather than normal XX condition. The condition is usually resulted by nondisjunction during maternal meiosis I but in few cases during meiosis II. The XXX condition is called trisomy of sex chromosome.

b.

The XXX aneuploidy occurs in females and resulted by nondisjunction of maternal chromosomes rather than in paternal chromosomes. If the condition is to occur through paternal chromosomes, it should be result in XXY condition rather than XXX. In case of aneuploidy resulted through paternal chromsomes' disjunction, it may take place in meiosis I and in few cases in meiosis II.