Question

How is the sex of a child determined in humans? Explain using a flow chart.

Hint:

Mother always gives X chromosome. Father gives X or Y. XX = Girl, XY = Boy.

Answer 1

Concept: In humans, sex determination depends on the type of sex chromosomes contributed by the parents during fertilization. Humans have 23 pairs of chromosomes, out of which one pair is the sex chromosomes.

• Females: XX (homogametic)
• Males: XY (heterogametic)

The mother always contributes an X chromosome, while the father can contribute either X or Y chromosome. Hence, the sex of the child is determined by the father. Explanation:

• All ova (eggs) produced by the mother carry only X chromosome.
• Sperms produced by the father are of two types:
  • X-bearing sperm
  • Y-bearing sperm
• Fertilization outcome:
  • X sperm + X ovum → XX (Female child)
  • Y sperm + X ovum → XY (Male child)

Flow Chart Representation: \[ \text{Father (XY)} \quad + \quad \text{Mother (XX)} \] \[ \begin{array}{c} \text{Father produces two types of sperms} \\ \downarrow
\text{X-sperm} \quad \quad \text{Y-sperm} \end{array} \] \[ \begin{array}{c} \text{Mother produces ova (only X)} \\ \downarrow \end{array} \] \[ \begin{array}{ccc} X \text{ (ovum)} + X \text{ (sperm)} & \Rightarrow & XX \text{ (Girl)} \\ X \text{ (ovum)} + Y \text{ (sperm)} & \Rightarrow & XY \text{ (Boy)} \end{array} \] Conclusion: The sex of a child in humans is determined by the type of sperm (X or Y) that fertilizes the ovum. Therefore, the father is responsible for determining the sex of the child.