How many pairs of chromosomes are present in human beings? Out of these how many are sex chromosomes? How many types of sex chromosomes are found in human beings? "The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it". Draw a flow chart showing determination of sex of a newborn to justify this statement.

Chromosomes in Human Beings

• Total pairs of chromosomes: There are $23$ pairs of chromosomes present in human beings (total of $46$ chromosomes).
• Number of sex chromosomes: Out of these, exactly $1$ pair (i.e., $2$ chromosomes) are sex chromosomes.
• Types of sex chromosomes: There are $2$ types of sex chromosomes found in human beings, namely the $X$ chromosome and the $Y$ chromosome.

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Justification: "The sex of a newborn child is a matter of chance"

In human beings, the sex of a child is genetically determined at the moment of fertilization:

1. Maternal Contribution: Women have a perfect pair of sex chromosomes ($XX$). Therefore, all eggs produced by a mother carry only one type of sex chromosome, which is the $X$ chromosome.
2. Paternal Contribution: Men have a mismatched pair of sex chromosomes ($XY$). Therefore, half ($50\%$) of the sperms carry an $X$ chromosome, and the other half ($50\%$) carry a $Y$ chromosome.
3. Random Fertilization:

• If an $X$-bearing sperm fertilizes the egg ($X$), the resulting zygote is $XX$, which develops into a girl.
• If a $Y$-bearing sperm fertilizes the egg ($X$), the resulting zygote is $XY$, which develops into a boy.

Since the fusion of either an $X$ or a $Y$ sperm with the egg is a completely random event, there is an exact $50\%$ (1:1) chance for either outcome. Thus, the sex of the child is a matter of pure chance, and neither parent can be held responsible for it.

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Flow Chart of Sex Determination