Question

Due to nondisjunction of the sex chromosomes in males, some of the sperms carry 22+XY while others carry 22+O.

Which of the following syndromes are likely to appear in the offspring if these sperms fertilise normal eggs carrying 22+X?

• A. Edwards syndrome and Down’s syndrome
• B. Cri-du-chat syndrome and Klinefelter’s syndrome
• C. Klinefelter’s syndrome and Down’s syndrome
• D. Klinefelter’s syndrome and Turner’s syndrome

Answer 1

The correct option is D Klinefelter’s syndrome and Turner’s syndrome

Sperms and eggs are gametes which on fusion result in the formation of the zygote. The sperms carry 22 autosomes and either X or Y chromosomes. The eggs carry 22 autosomes and X chromosome.

Gametes are produced by meiosis and during meiosis, if the homologous chromosomes or sister chromatids fail to separate (nondisjunction), it results in chromosomal abnormalities in eggs and sperms.

If the normal egg (22+X) is fertilised by the sperm carrying 22+XY (aneuploid sperm), it will result in the offspring developing Klinefelter’s syndrome as the zygote will have 44+XXY chromosome complement.

If the normal egg (22+X) is fertilised by the sperm carrying 22+O (aneuploid sperm), it will result in a zygote with 44+XO. Hence, the offspring will suffer from Turner’s syndrome.

In the given question, the nondisjunction is seen in the sex chromosomes and not in the autosomes and thus the resulting offspring will neither have Edwards syndrome nor Down’s syndrome.

Edwards syndrome is a chromosomal disorder caused due to nondisjunction of the 18th chromosome (autosome) that results in the trisomy of the 18th chromosome.

Down’s syndrome is a chromosomal disorder caused due to nondisjunction of the 21st chromosome (autosome) that results in trisomy of the 21st chromosome.

Cri-du-chat syndrome is caused due to the deletion of part of the 5th chromosome.