Q11 of 47 Page 77

A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.

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.


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.


Only daughters indicate the fusion of egg with sperms carrying 22+X chromosomes every time.


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