Question

Given below are two statements:
Statement I: Down's syndrome is caused by the absence of one of the X-chromosomes.
Statement II: Turner's syndrome is caused by the presence of an additional copy of the chromosomes.
In the light of the above statements, choose the correct answer from the options given below:

• A. Statement I is incorrect but Statement II is correct
• B. Both Statement I and Statement II are correct
• C. Both Statement I and Statement II are incorrect
• D. Statement I is correct but Statement II is incorrect

Hint:

Down's syndrome results in a total of \(47\) chromosomes due to autosomal trisomy. Turner's syndrome results in a total of \(45\) chromosomes due to sex chromosome monosomy. Klinefelter's syndrome is another key sex-chromosome aneuploidy, involving an extra X chromosome (\(XXY\), \(47\) chromosomes).

Answer 1

The Correct Option is C

Concept:

• Aneuploid disorders are caused by the gain or loss of specific chromosomes due to non-disjunction during cell division.

• Down's Syndrome: Caused by the presence of an extra copy of autosome 21 (Trisomy 21). It is an autosomal disorder and does not involve sex chromosomes.

• Turner's Syndrome: Caused by the absence of one of the sex chromosomes (X chromosome) in females, leading to an \(XO\) karyotype with \(45\) total chromosomes.

Step 1: Evaluate Statement I
Statement I is incorrect: Down's syndrome involves an additional copy of chromosome 21, not the loss of an X chromosome.

Step 2: Evaluate Statement II
Statement II is incorrect: Turner's syndrome is caused by the absence of a chromosome (monosomy \(XO\)), not by an additional copy of a chromosome.

Step 3: Select the corresponding option
Since both Statement I and Statement II are incorrect, option (3) is the correct choice.