Sex determination in humans takes place by

Sex determination in humans takes place by sex chromosomes of father.

Sex chromosomes are a pair of chromosomes that determine whether a person is male or female. Human sex chromosomes are divided into X and Y chromosomes. There are two X chromosomes in women, while men have one X chromosome and one Y chromosome. During meiosis, the male XY sex chromosome pair segregates and transfers either X or Y to the isolated gamete. For example, half of the sperm have an X chromosome and the other half have a Y chromosome. All female oocytes generally carry a single X. After fusion of  male and female gametes, the zygote carries either XX or XY, depending on whether sperm containing X or Y have fertilized the oocyte. When an oocyte is fertilized by a sperm with X, it becomes female (XX), and fertilization by  a sperm with Y becomes male (XY).

Therefore, the correct answer is option A.