question_answer

(i) Explain why a recessive allele is unable to express itself in heterozygous state.

(ii) In human being, the sex of the child is determined by the father and not by the mother. Explain.

Answer:

(i) A recessive allele is unable to express itself in heterozygous state due to the presence of a dominant allele. According to Mendel?s law of dominance, in a dissimilar (heterozygous) pair of factors which occur in pairs, one member will be dominant and other will be recessive. The dominant allele will always suppress the expression of recessive allele.

(ii) As a rule, the heterogametic organism determines the sex of the unborn child. In case of humans, since males are heterogametic it is the father and not the mother who decides the sex of the child.

Males produce two types of gametes X and Y, while females produce only one type of ovum, X.

The sex of a child is determined at the time of fertilisation. If male gamete containing X-chromosome fertilises the ovum, the child would be female, if Y-chromosome does it, the child would be male.