How do new alleles occur?

How are new alleles created? Occasionally, DNA mutations occur in germ cells - cells destined to become eggs or sperm. In this case, the DNA mutation is copied into every new cell of the growing embryo following fertilisation ... If the mutation affects a gene, it will result in a new version of that gene - a new allele.

Mitosis; the process of mitosis splits the cell into two, making the one allele (gene) become two daughter cells (cell division)