Q3 of 32 Page 32

Does the sex of the child depend on the father or it is just a matter of chance? Discuss.

The two chromosomes that determine the sex of the unborn baby are called sex chromosomes named X chromosomes and Y chromosomes. A female has two X chromosomes, while a male has one X and one Y chromosome. The gametes (egg and sperm) have only one set of chromosomes. Thus, in females, all the egg cells contain X chromosomes while in males, half sperm have X chromosomes and half sperms have Y chromosomes.

The sex of the child depends upon the kind of sperm that fertilizes the egg. It is simply a matter of chance as to which category of sperm fuses with the ovum.


When a sperm containing X chromosome fertilizes the egg, the zygote would have XX chromosomes and develop into a female child.


If the sperm contributes a Y chromosome to the egg (ovum) at fertilization, the zygote would develop into a male child.


Thus, father is responsible for the sex of the baby which is born.


More from this chapter

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1

Explain the following terms:

(a) Heterozygous


(b) Homozygous


(c) Pedigree chart.

 2

State the three Mendel's laws of inheritance.

 1

In a certain species of animals, black fur (B) is dominant over brown fur (b). Predict the genotype and phenotype of the offspring when both parents are 'Bb' or have heterozygous black fur.

 2

Two pairs (A & B) of rabbits were crossed as given below:


(a) Can you tell which coat' colour (black or white) is dominant? ………………………….


(b) Is the coat colour sex-linked? …………….