Chapter Summary

The brief account of the basic facts of genetics demonstrates two important points relative to evolution.

1. It is important to understand that all phenotypic traits are, initially, the products of the genetic code. Thus, evolutionary change is at its most basic level genetic change. But the pathway from genetic code to phenotypic traits is a complex one. A gene simply codes for the synthesis of a protein. Proteins build cells, run their chemical reactions, link them together, and help them communicate; cells make up tissues, which in turn make up the body of a living organism—humans as well as pea plants. Moreover, this complex process is affected by environmental factors, so that the genetic code is most definitely not soley responsible for the final form and function of a living being. As we try to explain the phenotypic changes we see in evolution, we must keep these ideas in mind, for if the genetic process itself is complex, so, then, are the processes of evolution that act to change it.

2. The very process by which organisms pass on traits from parent to offspring also accounts for the variation seen between generations and among members of a species. If inheritance produced offspring that were exact copies of their parents, no change would ever take place and there would be no evolution—no adaptation, no change through time, and no new species. But segregation, independent assortment, crossing over, and recombination mix existing genetic combinations (sort of like shuffling a deck of cards), and mutation produces new genetic variation.

We will look more closely at sources of variation and the processes of evolution in the next chapter.

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