Question

If the female gamete carries 22+XX chromosomes, while male gamete is normal, predict the probable defects in the baby formed as a result of fusion between these gametes from the options given below.

i. Triple X syndrome
ii. Klinefelter’s syndrome
iii. Turner’s syndrome
iv. Edwards' syndrome
[1 mark]

• A. i and ii
• B. ii and iii
• C. i and iv
• D. iii and iv

Answer 1

The correct option is A i and ii

Gametes are haploid cells. The number of chromosomes in human gametes (egg and sperm) is 23.

The normal male gametes (sperms) in humans have 22 autosomes and one X or Y chromosome (22+X or 22+Y).

The normal female gametes (eggs) in humans have 22 autosomes and one X chromosome (22+X).

The female gamete mentioned in the question carries two copies of the X chromosome instead of a single copy in the egg. So the condition is 22+XX. The probable reason for this might be nondisjunction (failure of separation of homologous chromosomes during meiosis I or failure of separation of sister chromatids during meiosis II).

If the sperm (22+X) fertilising the egg (22+XX) carries an X chromosome, then the zygote formed will carry 44 autosomes and XXX sex chromosomes. This will lead to triple X syndrome in the female offspring (22+XXX).

If the sperm (22+Y) fertilising the egg (22+XX) carries a Y chromosome, then the zygote formed will carry 44 autosomes and XXY sex chromosomes. This will result in Klinefelter’s syndrome in the offspring. The affected offspring will develop into sterile males. Hence option a is correct.

This has been explained via the following cross:


Edwards' syndrome is a genetic condition in babies that causes severe disability. It is caused by an extra copy of chromosome 18 (trisomy). Here the condition is 45+XX or 45+XY.

Turner's syndrome is a genetic disorder affecting females. This is caused by the missing of one X chromosome. So the condition here is 44+XO.