Figure 24.10

Variations in eye color. A model of two genes, with two alleles each, can explain five human eye colors.

of protein called a transcription factor, which switches on other genes that direct development of male structures in the embryo, while suppressing formation of female structures. Because a female lacks a Y chromosome, she also lacks an SRY gene, and the "default" option of female development ensues. Figure 24.12 shows the sex chromosomes.

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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