Introduction

Mendel's laws explained the patterns by which traits could seem to vanish in one generation and reappear in the next, and showed that this hereditary information is passed from parents to offspring on the chromosomes. One of the more advanced later insights was that an organism's characteristics are actually encoded in molecules of DNA, which directs the construction of proteins — the molecules that shape cells and drive the chemical reactions of life, including metabolism and photosynthesis. Every organism's genome, the complete set of nucleic-acid sequences carrying its hereditary information, may be split across several nucleic acid molecules, each carrying many genes, and each gene is itself a sequence that represents a single protein.

This chapter traces that story forward: the structure of DNA, how it replicates, how RNA is transcribed from it, the genetic code that specifies amino-acid sequences during translation, how gene expression is regulated, and the essentials of human genome sequencing.