The possibility of a female becoming haemophilic is extremely rare because mother of such a female has to be at least `overset("(i)") "____"` and father should be `overset("(ii)") "____"`

Options

A. (i) haemophilic, (ii) carrier
B. (i) carrier, (ii) haemophilic
C. (i) haemophilic, (ii) normal
D. (i) haemophilic, (ii) haemophilic

Answer

B

Explanation

Haemophilia is genetically due to the presence of a recessive sex linked gene h, carried by X-chromosome. A female becomes haemophilic only when both its X-chromosomes carry the gene `(X^(h)X^(h))` However. Such females generally die before birth because the combination of these two recessive alleles is lethal. A female having only one allele for normal blood clotting present on the other X-chromosome is dominant. Such females are known as carriers. In case of males, a single gene for the defect is able to express it self as the Y-chromosome is devoid of any corresponding allele (X^(h)Y)`. The possibility of human female becoming haemophilic is extremely rare because she has to be homozygous recessive for the trait, i.e., her father must be haemophilic and mother must be atleast a carrier.