2 Genotype and Color

Before working on this section, find the Reset link at a the upper-right corner of your Ducks & Gators window and click on it:

The Reset link.
The Reset link.

This will refresh the window and restore all settings to their default values.

Directly under the duck pond is a table of duck genotypes and the corresponding duck colors:

Table of genotypes and phenotypes.
Table of genotypes and phenotypes.

Feather color in the virtual ducks is determined by a single gene—the A gene—with two alleles: A1 and A2. Under the default settings, ducks with genotype A1A1 are bright yellow, ducks with genotype A1A2 are tan, and ducks with genotype A2A2 are brown. However, you can change the phenotype associated with each genotype. The colored boxes are popup menus, allowing you to assign any one of ten colors to any of the three possible genotypes:

The phenotype popup menu. (Ducky cartoon by jameslee1 / iStock.)
The phenotype popup menu. (Ducky cartoon by jameslee1 / iStock.)

You can pick the same color for all three genotypes:

No variation in phenotype.
No variation in phenotype.

You can pick a unique color for each genotype:

Each genotype has a unique phenotype.
Each genotype has a unique phenotype.

Or you can pick any other combination of phenotypes you like.

We will refer to the table of genotypes and phenotypes as the “genetic model” for a population of virtual ducks. As you have just seen, you can set up a large number of different genetic models.

  1. In fact, you can set up exactly 1,000 different genetic models in Ducks & Gators. Explain why.

You may recall, from your previous experience with genetics, the terms dominant” and “recessive.” For reasons I hope to help you understand more clearly in this tutorial, these terms can be confusing—even misleading. An argument can be made that we would all be better off if we stopped using them altogether. However, because you have heard the terms before—and will undoubtedly hear them again—it will be useful to carefully consider and discuss these questions:

  1. How can you set up a genetic model in which allele A1 is dominant with respect to color? Give two examples.

  2. How can you set up a genetic model in which allele A1 is recessive with respect to color? Give two examples.

  3. How can you set up a model in which heterozygotes have a phenotype intermediate between the phenotypes of A1A1 and A2A2 homozygotes? Give two examples.

  4. How can you set up a model in which heterozygotes have a phenotype outside the range bracketed by A1A1 and A2A2 homozygotes? Give two examples.

As you work through this tutorial, remember that in Ducks & Gators you always have complete control of the relationship between genotype and color. That is, you choose the genetic model. And genotype is the sole determinant of color.