Overview & Objectives


In this lesson, you’ll take a look at dihybrid test cross data in corn and determine if independent assortment, pleiotropy, or linkage of genes is at work for these traits. We’ll describe what linked genes are, the units of measurement for linkage mapping, two ways to calculate linkage, and how the data from multiple crosses can be used to assemble a chromosome map.

Through this lesson, you’ll gain the foundation for understanding the biological and mathematical basis of chromosome/linkage/gene maps that are available today.


At the completion of this lesson, you will be able to:

  1. Contrast the inheritance of traits that are controlled by independent genes and by linked genes.
  2. Demonstrate the physical basis of linkage by drawing the key events in meiosis.
  3. Calculate map distances from 2-point test cross and F2 data.
  4. Assemble linkage maps from map distance information.

Original lesson created by Don Lee in 2001. Lesson updated by Don Lee & McKinzie Sutter in 2023.

Development of this lesson in 2001 was supported in part by Cooperative State Research, Education, & Extension Service, U.S. Dept of Agriculture under Agreement Number 98-EATP-1-0403 administered by Cornell University and the American Distance Education Consortium (ADEC).  Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

In 2023, Dr. Don Lee and McKinzie Sutter updated the lesson with new images and a slight change in the presentation of the information.