Correct Option
The correct option isThe sex chromosomes of the father.
Explanation
In humans, sex determination is governed by the XX-XY chromosomal system. The sex of the offspring is established at the time of fertilization based on the chromosomal composition of the gametes involved.Mechanism of Sex Determination:
- Female Gametes (Homogametic): Human females possess two identical sex chromosomes (XX). Consequently, all ova (eggs) produced by a female contain a single X chromosome.
- Male Gametes (Heterogametic): Human males possess two different sex chromosomes (XY). During spermatogenesis, males produce two types of sperm in equal proportions:
- 50% of sperm carry the X chromosome.
- 50% of sperm carry the Y chromosome.
- Fertilization Event:
- If an ovum is fertilized by a sperm carrying an X chromosome, the resulting zygote is XX (Female).
- If an ovum is fertilized by a sperm carrying a Y chromosome, the resulting zygote is XY (Male).
Since the female always contributes an X chromosome, the variable factor is the sex chromosome contributed by the male. Therefore, the genetic sex of the child is determined exclusively by the father's sperm.
Key Takeaway: Human males are heterogametic (XY) and produce two types of sperm. The sex of the offspring is determined by whether an X-bearing or Y-bearing sperm fertilizes the egg.