Question

Hemophilia is a hereditary disease carried by
A. Males and expressed by females
B. Females and expressed by males
C. Female and expressed by female
D. Males and expressed by males.

Answer 1

Hint:- Hemophilia is a genetic disorder in which your blood has not clot normally due to the absence of sufficient blood-clotting proteins also called clotting factors. If you are suffering from hemophilia, you would bleed for a long time after an injury than you may if your blood clotted normally.

Complete Answer:-
The gene that encode clotting factor is present on X chromosome, as we know that in humans a male contains XY combination of sex chromosomes while human female represents XX combination of sex chromosomes, due to the presence of single X chromosome male have only single gene for clotting factor while female having two sets of gene encoded clotting factor. If a gene present on X chromosome is mutated or silent in case of male so male would be suffering from haemophilia while females are carrier because they have two sets of genes, if one gene is unable to express a gene present on another X chromosome will be expressed clotting factors. Hence, females would be hemophiliac, if she has both default genes on the both X chromosomes.
Females would be carriers or might express this disorder but it is always expressed in males if the default gene is present.
As per the above discussion the correct answer of this question is option, B Females and expressed by males.

Note:- Female progeny gets X chromosomes form both the parents and male progeny gets X chromosome form mothers and Y chromosome from fathers. Boys always inherited this disorder from mother and girls would be inherited from haemophilia from both parents.