Introduction

Genetics is the branch of biology that studies how living things pass their traits from one generation to the next. Few fields have reshaped the world as much as genetics has in the last half-century, and its advances now underpin large parts of agriculture, medicine and forensic science. At its core, genetics is the science of heredity - it deals with the mechanism by which characters are transmitted from parents to offspring. The term itself was coined by W. Bateson in 1906.

The subject is conventionally split into four major subdisciplines. Transmission genetics, also called classical genetics, deals with how genes pass from parents to offspring, and its foundations rest on Gregor Mendel's study of seven contrasting trait-pairs in the garden pea. Molecular genetics looks instead at the structure and function of a gene at the molecular level. Population genetics studies heredity across groups of individuals for traits governed by a small number of genes, while quantitative genetics studies traits in populations shaped by many genes acting together.

Underlying every one of these subdisciplines is the gene - the basic, functional unit of heredity, the unit of biological information that carries biochemical, anatomical and behavioural traits from parents to their offspring.