“The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it.” Justify this statement with the help of flow chart showing determination of sex of a newborn.

Justification:

1. Genetic Contribution of Parents:

• Human females have a perfect pair of sex chromosomes ($XX$). Therefore, all female gametes (eggs) carry only one $X$ chromosome.
• Human males have a mismatched pair of sex chromosomes ($XY$). Therefore, male gametes (sperms) are of two types: $50\%$ carry the $X$ chromosome and $50\%$ carry the $Y$ chromosome.

1. Role of Chance:

• The sex of the child is determined entirely by which type of sperm fertilizes the egg.
• If a sperm carrying the $X$ chromosome fertilizes the egg ($X$), the resulting zygote is $XX$ (female/girl).
• If a sperm carrying the $Y$ chromosome fertilizes the egg ($X$), the resulting zygote is $XY$ (male/boy).

1. Equal Probability:

• Since fertilization is a completely random event, there is an exact $50\%$ ($1:1$) chance of either an $X$-bearing or a $Y$-bearing sperm fusing with the egg. Thus, sex determination is a matter of pure chance, and neither parent is responsible.

Punnett Square:

$$\begin{array}{c|cc} \text{Male Gametes (Sperms)} \backslash \text{Female Gametes (Eggs)} & X & X \\ \hline X & XX \text{ (Girl)} & XX \text{ (Girl)} \\ Y & XY \text{ (Boy)} & XY \text{ (Boy)} \end{array}$$