Students often become confused as they count from one decade to the next. In order to become fluent with operations in addition and subtraction, students need to be able to move across decades. This lesson includes a detailed activity, video and pictures of students at work, and an extension idea.

See how an X or Y chromosome carried by a sperm cell, determines the sex of the offspring in this video. [5:52]

Biology 2e is designed to cover the scope and sequence requirements of a typical two-semester biology course for science majors. The text provides comprehensive coverage of foundational research and core biology concepts through an evolutionary lens. Biology includes rich features that engage students in scientific inquiry, highlight careers in the biological sciences, and offer everyday applications. The book also includes various types of practice and homework questions that help students understand—and apply—key concepts. The 2nd edition has been revised to incorporate clearer, more current, and more dynamic explanations, while maintaining the same organization as the first edition. Art and illustrations have been substantially improved, and the textbook features additional assessments and related resources.

By the end of this section, you will be able to do the following:

Discuss Sutton’s Chromosomal Theory of Inheritance
Describe genetic linkage
Explain the process of homologous recombination, or crossing over
Describe chromosome creation
Calculate the distances between three genes on a chromosome using a three-point test cross