Through drift, these new alleles may become more common within the population.

This means that new alleles can have a difficult time invading a population, since they don't experience significant benefit until they become common.

The wide range and complex environment selected for new alleles and promoted their expansion.

Mutation is the ultimate source of genetic variation in the form of new alleles.

DNA sequences can change through mutations, producing new alleles.

In 1994, a new allele of reeler was obtained by means of insertional mutagenesis.

Mutations are random changes in genes, and can create new alleles.

The combination of mutations creating new alleles at random, and natural selection picking out those that are useful, causes adaptation.

Classical geneticists would have used phenotypic traits to map the new mutant alleles.