Final answer:
The sex of a baby is determined by the father's contribution: an X chromosome results in a female child, while a Y chromosome results in a male child. Mothers consistently contribute an X chromosome, ensuring that the father's gametes ultimately decide the baby's sex. Nettie Stevens was pivotal in identifying these patterns of sex-linked inheritance.
Step-by-step explanation:
At the core of the differences between gender and sex is the chromosomal information transmitted at the moment a child is conceived. The mother contributes an X chromosome and if the father contributes a Y chromosome, a male would be produced.
If a baby inherits an X chromosome from the father and an X chromosome from the mother, the child's sex will be female, as females have two X chromosomes (XX). Conversely, if the father's sperm carries the Y chromosome, the child will be male, characterized by having one X and one Y chromosome (XY). The sex of the baby is determined by the father because mothers can only pass on an X chromosome. Fathers have a 50 percent chance of passing on the Y or X chromosome, thereby creating a 50:50 chance that a child will be male or female.
In sexual reproduction, gametes with either an X or Y chromosome are formed in males, while gametes in females contain a single X chromosome. Pioneering scientist Nettie Stevens significantly contributed to our understanding of how sex-linked inheritance works by observing chromosomal differences and establishing that the Y chromosome is crucial for the development of male characteristics.