The correct answer is b) the Y chromosome in the zygote.
Explanation:
The Y chromosome contains the SRY gene, which triggers male development.
In humans, sex is determined by the sex chromosomes (X and Y). Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
The egg cell always carries an X chromosome, so the sex of the child is determined by whether the sperm cell carries an X (resulting in a female) or a Y (resulting in a male) chromosome.
Why other options are incorrect:
a) the X chromosome in the zygote:
While the X chromosome is present in both males and females, the presence of the Y chromosome is what determines maleness.
c) the cytoplasm of germ cell which determines the sex:
The cytoplasm of germ cells plays a role in the development of primordial germ cells, but it doesn’t directly determine the sex of the child.
d) sex is determined by chance:
While there’s a 50/50 chance of inheriting an X or Y chromosome from the father, it’s not random in a biological sense. The presence of the Y chromosome triggers male development, so it’s not simply a matter of chance.