Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 231

Self‐pollination is considered the highest degree of inbreeding a plant can achieve. It promotes homozygosity of all gene loci and traits of the sporophyte. Consequently, should there be cross‐pollination the resulting heterozygosity is rapidly eliminated. To be classified as self‐pollinated, cross‐pollination should not exceed 4%. The genotypes of gametes of a single plant are all the same. Further, the progeny of a single plant is homogeneous. A population of self‐pollinated species in effect comprises a mixture of homozygous lines. Self‐pollination restricts the creation of new gene combinations (no introgression of new genes through hybridization). New genes may arise through mutation, but such a change is restricted to individual lines or the progenies of the mutated plant. The proportions of different genotypes, not the presence of newly introduced types, define the variability in a self‐pollinated species. Another genetic consequence of self‐pollination is that mutations (which are usually recessive) are readily exposed through homozygosity, for the breeder or nature to apply the appropriate selection pressure on (see Box 5.1).