A. Why is haemophilia generally observed in human males? Explain the conditions under which a human female can be haemophilic.

B. A pregnant human female was advised to undergo M.T.P. It was diagnosed by her doctor that the foetus she is carrying has developed from a zygote formed by an XX egg fertilized by Y-carrying sperm. Why was she advised to undergo M.T.P.?

Solution

A. Haemophilia is sex-linked recessive disease; it is transmitted from unaffected female carrier to male child with haemophilia. It is an X-linked recessive gene.
The females have XX condition and thus may be heterozygous carrying one normal X chromosome and diseased/affected X. Since the disease is a recessive one, therefore, it does not express until it is present in the homozygous condition.
The males have XY condition. The presence of the diseased allele of X will result in the person to develop the disease. The Y has no allele for this disease. Thus the probability of the males getting affected is much more than the females.

B. MTP stands for medical termination of pregnancy (MTP) or it may be called as abortion in common language.
The egg usually has one of the two X-chromosomes, but in this case, the pregnant female has egg having XX condition. The doctor advises for M.T.P. because her foetus may be carrying an abnormal number of chromosomes as the fertilisation of the XX egg by the Y sperm will create a trisomy condition.

It will result in a zygote having XXY condition, It will lead to nondisjunction abnormality such as Klinefelter syndrome where males may have an extra X chromosome. The child may suffer from abnormalities and thus the female was advised to have termination of pregnancy.

Some More Questions From Principles of Inheritance and Variation Chapter

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Principles Of Inheritance And Variation

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