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Inbreeding is also used to reveal deleterious recessive alleles, which can then be eliminated through assortative breeding or through culling. In plant breeding, inbred lines are used as stocks for the creation of hybrid lines to make use of the effects of heterosis. Inbreeding in plants also occurs naturally in the form of self-pollination.
An example of inbreeding depression is shown in the image. In this case, a is the recessive allele which has negative effects. In order for the a phenotype to become active, the gene must end up as homozygous aa because in the geneotype Aa, the A takes dominance over the a and the a does not have any effect. Some recessive genes result in ...
Genetic purging is the increased pressure of natural selection against deleterious alleles prompted by inbreeding. [1]Purging occurs because deleterious alleles tend to be recessive, which means that they only express all their harmful effects when they are present in the two copies of the individual (i.e., in homozygosis).
[1] [2] The term is generally used to mean the chance or ability of a population to avoid the problems of inbreeding. [1] Less commonly genetic viability can also be used in respect to a single cell or on an individual level. [1] Inbreeding depletes heterozygosity of the genome, meaning there is a greater chance of identical alleles at a locus. [1]
Inbreeding tends to occur in flocks of limited size and where only a single or a few rams are used. Associated with inbreeding is a decline in progeny performance usually referred to as inbreeding depression. Inbreeding depression has been found for lamb birthweight, average daily weight gain from birth until two months, and litter size. [38]
Inbreeding avoidance occurs in nature by at least four mechanisms: kin recognition, dispersal, extra-pair/extra-group copulations, and delayed maturation/reproductive suppression. [ 3 ] [ 12 ] These mechanisms are not mutually exclusive and more than one can occur in a population at a given time.
Line breeding is differentiated from inbreeding by excluding pairings between parents and offspring, and between full siblings. Outcrossing is the planned breeding between two unrelated dogs, used to increase genetic diversity in a breed and decrease genetic issues or abnormalities inherited from line breeding or inbreeding.
The effect of inbreeding on reproductive behavior was studied in the poeciliid fish Heterandria formosa. [2] One generation of full-sib mating was found to decrease reproductive performance and likely reproductive success of male progeny.