Which statement about inheritance is true?

In humans, an egg usually contributes an X chromosome, while a sperm contributes either an X or a Y chromosome. An X-bearing sperm typically results in an XX offspring, and a Y-bearing sperm typically results in an XY offspring, so the father determines the offspring’s chromosomal sex. A carrier mother does not pass an X-linked disease to every son; each son has a 50% chance of inheriting her affected X chromosome.

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