Question

The maleness of a child is determined by
(a) The X chromosome in the zygote
(b) The Y chromosome in the zygote
(c) The cytoplasm of germ cell which determines the sex
(d) Sex is determined by chance

Answer 1

Humans have 46 chromosomes out of which one pair is the sex chromosome and it differs from an ordinary autosome in size and behavior. It is concerned with the the sex of an organism.

Complete answer:
Multi-cellular organisms have special cells called gametes for reproduction which contain only half the number of chromosomes. So when gametes from two different parents combine during reproduction, it results in a new individual, which contains DNA (the genetic material passed from parents) and re-established a number of chromosomes. This process is done by many species to produce their off-spring as it is the only means to ensure the continuity of a species.
Humans usually have 23 pairs of chromosomes i.e. a total of 46 chromosomes. The autosomes (1-22 chromosome pairs) are the same in males and females. Chromosome pair 23 is dissimilar for males and females i.e. females have two X chromosomes, whereas males have an X chromosome and a much smaller Y chromosome. This 23rd pair determines the sex of the human. If the Y-chromosome in zygote is inherited from the father then it is a male and if the X-chromosome is inherited from the father, the zygote will develop into a girl.
So, the correct answer is ‘The Y chromosome in the zygote’.

Note: X chromosome contains a large amount of euchromatin (a lightly packed form of chromatin) and small amount of heterochromatin (condensed chromatin structure) whereas; Y chromosome contains a small amount of euchromatin and large amount of heterochromatin. Genes present in the X chromosome shows criss cross inheritance and genes present in the Y chromosome shows linear inheritance.