Role of the Sex Chromosomes

Most of our cells have 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (see fig. 4.15, p. 146). A sex chromosome can either be a large X chromosome or a small Y chromosome. Every egg contains an X chromosome, but half of the sperm carry an X while the other half carry a Y. If an egg is fertilized with an X-bearing sperm, it produces an XX zygote that is destined to become a female. If it is fertilized with a Y-bearing sperm, it produces an XY zygote destined to become a male. Thus the sex of a child is determined at conception (fertilization), and not by the mother's egg but by the sperm that fertilizes it (fig. 27.1).

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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