Also known as Mendel's Second Law, the principle of independent assortment holds that genes are inherited independently of each other.

Mendelism is an atomistic theory of heredity. Not only are there discrete genes that encode discrete proteins, but also the genes are preserved during development and passed on unaltered to the next generation.

Mendel (pictured opposite) demonstrated that an organism inherits an allele from each of its two parents - this is the law of segregation. The phenotypes of mothers and fathers often appear to blend in their offspring, and consequently most students of heredity before Mendel thought that inheritance involved some sort of blending of genes. In fact, the underlying genes are preserved.

Why does the preservation of genes matter for Darwinism?