Module 6 Lesson 6 - 1

Get Focused

On the top of a chicken's head is a fleshy growth known as its comb. Chicken combs have four possible phenotypes: rose, pea, walnut, and single. In earlier lessons, if you had been presented with this information, you likely would suspect multiple alleles were responsible for this trait. However, a walnut chicken can be crossed with another walnut chicken and their offspring can display all four of the possible phenotypes. That would not be possible with any amount of alleles if this trait was explained by a single gene. This type of inheritance could be possible only if more than one gene was acting to produce the same trait!

In this lesson, you will study traits controlled by many genes. You will recognize inheritance patterns that show gradual changes in phenotypes, and you will understand that the expression of one gene can turn the expression of another on or off.

Our environment can influence our genes significantly. Sun exposure triggers the expression of many of genes in plants and animals. Exposure to water can change the development of leaves in the same plants. Changes in temperature cause the expression of dark pigment in some rabbits and in Siamese cats. These are very specific examples, but the way the environment affects gene expression is open for more discussion.

In this lesson, you will examine the effect the environment may have on the expression of genes.

This lesson has two focusing questions:

• How might multiple genes combine to form a single trait?
• How does the environment affect the expression of genes?