Question

Assertion : Females, homozygous for genes on the $X$ chromosomes do not express a trait more markedly than do hemizygous males.
Reason : Dosage compensation mechanism accounts for effective dosage genes in males and females.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (A)

Females have two $X$ chromosomes and males have only one $X$ chromosome. Thus, a dosage compensation mechanism must be present through which the effective dosage of genes of the two sexes is made equal. This is achieved by inactivation of one $X$ chromosome in females which gets condensed and become heteropyknotic. Since only one $X$ chromosome is required for normal metabolism in cells of females, the other $X$ chromosome has the capability of being heterochromatic in some cells and euchromatic in others. Therefore, dosage compensation regulates the enzyme level of males and females.