Principles of Inheritance and Variation Question 57
57. The recessive genes located on X-chromosome in humans are always
(a) lethal
(b) sub-lethal
(c) expressed in males
(d) expressed in females
Show Answer
Answer : c
Hints & Solution
(c) Males have only one $X$ chromosome. Hence any gene present on the one $X$ chromosome expresses itself in males. Females have two $X$ chromosomes. The mutant allele must be present on both the $X$ chromosomes to express itself phenotypically. If only one copy of allele is present, then the female only becomes a carrier showing no external manifestation of the gene. Sublethal condition can never arise in males.
