How do new alleles occur?

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

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.