Chromosome Structure and Abnormalities — NEET Biology

Correct answer: A — Only S4 is correct

The core concept here is sex determination in humans, which is of the XY type, and the roles of male and female gametes. S1: Human males are heterogametic (XY), producing two types of sperms: 50% carrying X-chromosome and 50% carrying Y-chromosome. Thus, S1 is incorrect. S2: Females are homogametic (XX), producing only one type of ovum, which always carries an X-chromosome. Thus, S2 is incorrect. S3: Fertilization of an ovum (always X) by a Y-chromosome carrying sperm results in a male offspring (XY). Fertilization by an X-chromosome carrying sperm results in a female offspring (XX). Thus, S3 is incorrect. S4: In humans, out of 23 pairs of chromosomes, 22 pairs are autosomes and are exactly the same in both males and females. Thus, S4 is correct. S5: It is the genetic makeup of the sperm (carrying either X or Y) that determines the sex of the child, as the ovum always carries an X chromosome. Thus, S5 is incorrect. Therefore, only statement S4 is correct. The question tests the understanding of human sex determination, including gamete formation and the role of male vs. female in sex determination.