[rat-forum] Re: [rat-forum] How much allelic pleomorphism is seen in an inbred strain?

mbradbury nobody at no-reply.mcw.edu
Mon Mar 17 12:00:12 CST 2003


Inbred strains are defined by having been inbred for at least 20 generations with brother-sister matings, or other similar matings, such as parent-offspring. Many closed colonies of outbred animals slowly become inbred as genetic variation is lost through limiting which animals contribute to each generation as parents. However, it takes a LONG time to reach the same degree of inbreeding as inbred animals.That does not mean that they cannot suffer from inbreeding depression, especially if selection is applied to the breeding program, which further limits how many individuals of one generation are used to produce the next one. Commercial breeders can use computers to randomize mating of their outbred stocks to maintain outbred status, but smaller colonies don't usually work at it that hard, and some inbreeding occurs over time.

In theory, a true inbred strain will have no genetic variation between individuals, barring the difference in the X and Y chromosomes. This is not really achievable in practice, as mutations, genetic drift, and all those other factors work against it.

I am wondering about that number 8.3. Is that alleles or animals? Usually they come in integers either way. I would guess you have a closed coloni\y that is slowly becoming inbred, but it would not be an inbred strain at this point. I remember a paper where Falconer set up 20 lines of inbreeding from a single set of outbred mice. Most lines were lost after 6 generations of inbreeding due to inbreeding depression, more by the 6th generation, and only one made it all the way to 20 generations and inbred status. Inbreeding depression is real, and a problem in the long run for a closed colony if ignored.

Hope this helps,



Michael W. Bradbury, Ph.D.

Assistant Professor

Department of Medicine

Mount Sinai School of Medicine

Box 1039

1 Gustave L. Levy Place

New York, NY  10029

(212) 659-8363

More information about the rat-forum mailing list