Lesson 6 — Polygenic Traits


Lesson Summary

Polygenic inheritance is another example of an inheritance pattern that leads to a wide phenotypic variety in offspring. Look at groups of people in shopping malls or sports events. Can you spot many characteristics that have a continuous phenotype? Chances are that most of these are a result of polygenic inheritance.

Now, you can consider the nature versus nurture debate. When you consider who you are, from your personality to the unique shape of your nose, what do you think has had the greatest influence in the making of who you are? Was it the random assortment of genes that you received upon the uniting of your father's and mother's gametes? Has it been your environment and your upbringing that have allowed you to be taller, smarter, or funnier than those around you? Considering the variety of traits, such as height and behaviour, which do you believe is the definitive influence: genetics or environment?

Until this lesson, all inheritance patterns could be followed and predicted clearly. Adding the idea of our environment affecting our genes adds a very large amount of variance to understanding inheritance. Many genes might be present in individuals, but without the proper environmental exposure, they may never be expressed. As a result, the inheritance of traits may always happen according to the laws you have studied, but the expression of those traits may not always occur as predicted. Even with our knowledge of genetics, life can be surprising!

During this lesson, you were to examine two focusing questions:

  • How might multiple genes combine to form a single trait?
  • How does the environment affect the expression of genes?
Multiple genes can contribute to the expression of only one trait. Two genes may combine to form a new phenotype that neither can produce on its own. One gene may affect or control the expression of another gene by regulating a factor that is required by the other gene, such as pigment for hair cells. Many continuous phenotypes, such as corn length or bean mass, can be explained by each dominant allele of a gene collection being a greater contributor to the total. In each of these examples, genes combine to give rise to a single trait that can be observed.

Through your readings and from your exploration of temperature and gecko hatchings, you should see that the environment can have strong and dynamic influences on gene expression. This influence accounts for some of the variance in traits such as height. Whether this environmental effect on the expression of genes is stronger than the specific inheritance of those genes is still debated.


Assignment

Complete the Lesson 6 set of questions in Assignment 6B and Assignment 6D