Question

Colorblindness and Hemophilia A are X-linked recessive conditions. A woman heterozygous for hemophila mutation and a colorblind man have a son who is haemophilic and has Klinefelter's syndrome (XXY). Which of the following nondisjunction events is the most compatible with the situation described? Please provide an explanation

a. meiosis I, mother

b. meiosis II, mother

c. meiosis I, father

d. meiosis II, father

e. a and b

Answer 1

Ans. E (a and b)

A woman heterozygous for hemophila mutation and a colorblind man have a son is haemophilic and has Klinefelters syndrome (XXY).

haemophilia is a X-linked recessive disorder- these disorders are never passed from father to son.

in the X-linked recessive conditions A Hetrozygous mother acts as carriers and transmit this trait to half of their sons, and it is never passed from father to son.

so in the above case son is haemophilic means trait come from the mother.

in the process of cell cycle the normal separation of chromosomes and sister chromatids in meiosis I and Meiosis II recepctively is termed as disjunction.when this segregation is not normal then it is called as nondisjunction results production of gametes which have unusual number of chromosomes and is a common mechanism for the production of trisomy or monosomy. Nondisjunction is the process can occur either in meiosis I or meiosis II phases of cell cycle.

here is the example of the nondisjunction event of the one X-chromosome during meiosis I in the female leads to production of XXY Karyotype.

M-1 M-1 An An M-1 2n An in

this kind of nondisjunction may occur in Meiosis II also.