1. Tardigrade
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  3. Biology
  4. 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.

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Q. 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.

Principles of Inheritance and Variation

Solution:

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.