Selecting and breeding
Over many years farmers and breeders have selected the plants and animals with the best characteristics to be the parents of the next generations. This allows them to bring together the desired One of a number of forms of a particular gene. of two organisms thereby producing offspring superior to the parents.
Inbreeding
Inbreeding involves two closely related relatives reproducing. This is done for several generations until the population breeds true to the desired type due to the elimination of An individual with two different alleles of a specific gene.
Effects of inbreeding
While inbreeding can be used to develop desired characteristics, there can be negative results.
As seen in the illustration an effect of inbreeding can be an increase in the frequency of individuals who are homozygous for recessive deleterious alleles. These individuals will be less successful in surviving and therefore reproducing. The result is inbreeding depression. This can be expressed as a decline in vigour, size, fertility and yield of the species involved.
Crossbreeding and F1 hybrids
Due to the problems associated with inbreeding depression, inbreeding is rarely carried out indefinitely.
Crossbreeding animals
Instead in animals, new alleles are introduced by crossbreeding individuals from different breeds. This can produce a new crossbred population that have improved characteristics. The two parent breeds can be maintained to produce more crossbred animals that show the improved characteristic.The F2 produced by crossbreeding show a wide variation in genotypes.
In order to maintain the desired characteristics, the required F2 (second generation) are backcrossed with the parent or an individual with exactly the same genotype as the parent. This produces individuals that have the characteristics of both parents while maintaining the standard of the breed.
Crossbreeding plants
Hybridisation between two different homozygous inbred plants results in an F1 generation of hybrids that create a relatively uniform heterozygous crop.The F1 hybrids often display increased vigour, yield and fertility.
Constraints of inbreeding
If F1 hybrids of animals or plants are allowed to interbreed, the F2 generation will be genetically variable and of little use for further production. They may however contain new genotypes which increases variation and may be of use in the future.