Patent ID: 8753846

Claim:
A method of forming a selectable allele by double crossover homologous recombination in a host cell comprising: inserting into the host cell a donor DNA molecule comprising a first element of a first selectable allele, and at least two homology arms; wherein the donor DNA molecule can induce a first homologous recombination event between the donor DNA molecule and an acceptor DNA molecule comprising a second element of the first selectable allele in the host cell, thereby to form a product of the first homologous recombination event in the host cell; and wherein the donor DNA molecule can induce a second homologous recombination event within the product of the first homologous recombination event, thereby to form a product of the second homologous recombination event in the host cell which confers a selectable phenotype on the host cell, wherein the selectable phenotype arises following and in dependency on the formation of a selectable allele from the first and second elements of the first selectable allele; and wherein the host cell is a prokaryote.