In this lesson, we laid the foundation for understanding the biological and mathematical basis of chromosome maps. We looked at dihybrid test cross data in corn for the red vs. white and shrunken vs. plump traits and asked ourselves why we had so many more of certain phenotypes than others when we would expect even amounts for independently assorting genes. After looking at test cross data from several experiments, our best explanation was that the traits were linked. We used data from our experiments to calculate the map distance between the two genes. Later we conducted another experiment to learn about a waxy vs. normal seed trait and compiled a simple chromosome map of seed color, seed plumpness, and seed coat. Lastly, we showed how scientists can obtain map units between traits when only one genotype, the double recessive genotype, is known.

In the next linkage lesson (Linkage Part 2) we’ll expand your map creation abilities by calculating map distances for multiple-point data and genetic marker data.