What Is Genetics

Genetics is the science of investigating the relationship between parental and offspring characteristics; in other words, it's the study of heredity. For most of human history, people have understood that offspring tend to resemble their parents. Only relatively recently, beginning in the late 1800s, have we begun to understand how the genetic process works.

An easy way to think about genetics is to think about it in terms of information. In every cell of your body is a complete instruction manual for making a person, and somehow, these instructions get passed on to your offspring. The instruction manual is your DNA — basically a repository for all the instructions that make you, you.

As our understanding of the underlying mechanisms of genetics has increased, the field of genetics has expanded to include several new areas:

^ Molecular genetics is concerned with the biochemistry of DNA and genes, helping scientists understand exactly how DNA is replicated and transcribed. Molecular genetics is important to evolution because it helps clarify the process of mutation — that is, the errors that occur when something in the replication process goes awry. Most of these mutations are bad, but every so often, one of them results in something good. Mutations are the initial sources of the variations on which natural selection can act.

^ Genomics, a new branch of genetics, is concerned with the properties and information content of whole genomes. Comparing the genomes of different organisms gives us a better idea of how, for example, humans can be so different from chimps when they have most of the same DNA sequences. Looking at major genome-wide differences between people can help us understand the health implications of these differences.

^ Population genetics is the study of how the genetic variation that exists within groups of organisms changes over time. By studying large groups rather than individuals, scientists can observe the evolutionary process — some genes become more common, and others go extinct — to determine whether natural selection is involved.

Population geneticists can't use elephants or any other creature that has a long lifespan. Instead, they perform these studies with critters that don't live as long, such as bacteria. Sure, it takes some of the glamour out of the headlines, but the findings are still pretty amazing (to geneticists, anyway).

It's not always necessary to understand a process completely to make use of it. Although humans have only recently come to understand the details of how heredity works, we've been selectively breeding agriculturally important plant and animal types for thousands of years. For his part, Charles Darwin didn't understand exactly how it was that offspring resemble their parents; he just knew that they did. In the short span of this chapter, you'll discover more about genetics than Darwin ever knew! Because we now have a better understanding of the nuts and bolts of genetics and heredity, we are able to understand the evolutionary process in ways that Darwin could only dream of.

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