The word inheritance usually brings to mind money or property left by a relative who has passed away. But there’s another type of inheritance that is right under our noses—actually, your nose is part of the inheritance. Every living organism has characteristics or features that it passes on to its offspring. These tendencies of heredity are obvious: even a child knows cows give birth only to other cows, and that children often look like their parents. But, in fact, the specific biological mechanisms that allow parents to transmit their features to their offspring were an enormous mystery until about 140 years ago. Scientists back then knew that parents somehow made a tiny copy of themselves inside an egg or a sperm, but they had no idea what these copies were or how they worked.

Then, in the 1860s, an Austrian monk named Gregor Mendel started breeding peas in his garden. Where others saw only plants, Mendel looked deeper and found the basic units of heredity we now call genes. If you remember from the last chapter, genes are the parts of a chromosome that are transcribed to mRNA and are ultimately translated to the proteins essential to cellular processes. Mendel had no knowledge of protein synthesis and had never seen a chromosome, but his simple experiments with peas and the laws he developed to describe the behavior of hereditary—now termed classical genetics—have provided the foundation for the modern field of molecular genetics, the study of heredity on the molecular level.

For the SAT II Biology, you need a solid understanding of the basic laws and patterns of both classical genetics and molecular genetics. Questions on genetics can make up anywhere from 14 to 20 percent of the core of the SAT II Biology. In addition, the “M” section of the Biology E/M test focuses on evolution in terms of molecular biology, including genetics.