Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 21

One of the major advantages of bacteria for genetic studies is that they are haploid. This means that they have only one copy, or allele, of each gene. This property makes it much easier to identify cells with a particular type of mutation.

In contrast, most eukaryotic organisms are diploid, with two alleles of each gene, one on each homologous chromosome. Most mutations are recessive, which means that they do not cause a phenotype in the presence of a normal copy of the gene. Therefore, in diploid organisms, most mutations have no effect unless both copies of the gene in the two homologous chromosomes have the mutation. Backcrosses between different organisms with the mutation are usually required to produce offspring with the mutant phenotype, and even then, only some of the progeny of the backcross have the mutated gene in both homologous chromosomes. With a haploid organism such as a bacterium, however, most mutations have an immediate effect and there is no need for backcrosses.