A "girl gene," in the sense of determining female sex, is carried through the X chromosome, which is present in both males and females, but plays a different role in determining the sex of the child. A more accurate way to phrase the question is, "Which parent contributes the chromosome that guarantees a female offspring?"
According to the reference, a female offspring (girl) is created when a woman's X chromosome combines with a man's X chromosome.
Here's a breakdown:
- Females: Have two X chromosomes (XX).
- Males: Have one X and one Y chromosome (XY).
| Parent | Chromosome Contributed to Child | Possible Outcomes |
|---|---|---|
| Mother | X | X (always) |
| Father | X or Y | X (Girl), Y (Boy) |
Therefore:
- The mother always contributes an X chromosome.
- The father determines the sex of the child by contributing either an X chromosome (resulting in a girl) or a Y chromosome (resulting in a boy).
