Inbred line

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An inbred line is the almost pure hereditary progeny of a plant or animal that has emerged from close inbreeding , whose genetic origin ( gene pool ) is known, whose external ( phenotypic ) appearance and special properties are described in detail and whose pure-breeding reproduction is possible so that the described Characteristics are also retained in the subsequent generations.

Plant breeding

In plant breeding inbred lines are used and the basis of many successful Saatzuchtprogramme . With the artificial selfing of individual plants, there is an accumulation of (mostly) negative and (less often) positive gene combinations in the progeny. The proportion of stressed (depressed) offspring in free-flowering plants is around seventy percent. A positive gene combination only occurs in around ten percent of the offspring - these plants, in turn, are selfed.

After about seven generations of inbreeding, the progeny in maize breeding can be viewed as a pure-breeding inbred line and registered with the Federal Office for Plant Variety Protection to protect property rights . To optimize the time-consuming process, both growing seasons of the earth are used. After the harvest in autumn in the northern hemisphere, the seeds are taken to the southern hemisphere for sowing and then brought back in the spring after a further breeding step. From an economic point of view, the prerequisite for the creation of inbred lines is the short reproduction time and the low value of the individual plant or the individual.

Crossing two inbred lines creates F1 hybrids . The greater the genetic distance between the two true breeding lines, the higher the probability of high heterosis (performance achieved through crossing) of the hybrid. The best heterosis effects are achieved when the crossed inbred lines come from very distant genetic resources.

Animal breeding

Inbred lines of animal species are artificially generated, genetically homogeneous populations, which are necessary, among other things, for the standardization of scientific animal experiments . Mouse lines for breeding are particularly common (more than two hundred such lines are known).

In order to maintain a stable inbred line, it must be bred for at least twenty generations in consistent brother-sister pairing . During the breeding phase, inbreeding depression occurs , which can be overcome by purging . This is done through a strict selection of the breeding animals: More than 70% of the offspring are rejected because they are not sufficiently vital . The twentieth generation is 99.4% homozygous (pure breeding) and usually sufficiently stable in the expression of the desired characteristics.

The crossing of two inbred lines is called hybrid breeding . It is used to exploit the heterosis effect , which becomes stronger the greater the genetic distance between the inbred lines used. This method is used, for example, to raise laying hens .

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