Introduction

Genetics is the branch of biology concerned with heredity and variation — how characteristics and features are passed from parents to their offspring across successive generations. The basic unit of heredity is the gene, the inherited factor that determines an organism's biological characters, while variation is the extent to which offspring differ from their parents.

This chapter builds on that foundation to examine multiple alleles through the case of human blood groups, the mechanisms of sex determination in humans, insects and birds, sex-linked inheritance, Mendelian disorders linked to chromosomal abnormalities, and inheritance carried outside the nucleus. It closes by looking at eugenics, euphenics and euthenics as approaches aimed at improving the human race.