What is the probability that a pregnancy would result in a male child?

Analyze the question: It asks for the chance that a pregnancy produces a boy. This is a basic sex-determination genetics question.

Concept:

• Humans have 23 pairs of chromosomes, including one pair of sex chromosomes.
• Females are XX, and males are XY.
• The mother can only give an X chromosome in her egg.
• The father can give either an X or a Y in his sperm, with equal chance.

Step-by-step solution (Punnett square):

| | X (mother) | X (mother) | |---|---|---| | X (father) | XX (girl) | XX (girl) | | Y (father) | XY (boy) | XY (boy) |

The four possible outcomes are XX, XX, XY, XY.

• Number of male outcomes (XY) = 2
• Total outcomes = 4

Probability of a male child = 2/4 = 1/2

Why the others are wrong:

• A (3/4): there is no genetic basis for this ratio in sex determination.
• C (1): this would mean every child is male, which is not the case.
• D (1/4): this is the chance of a specific single genotype box, not of being male. Both XY boxes count.

Tip: The sex of the child is decided by the father's sperm, either X or Y, each with a 50% chance. So the chance of a boy is always 1/2, and the chance of a girl is also 1/2. This holds for every pregnancy, regardless of the sex of previous children.