Biomedical Engineering Reference
In-Depth Information
caused by an inner ear defect. In both cases, the mice were maintained
by mouse breeders in closed colonies in order to maintain these inter-
esting mutations, which were known to be recessive traits. Cancer biol-
ogists soon found that if they took a tumor that spontaneously arose in
one member of these closed colonies that they could often successfully
transplant them to another member of the colony. The tumor would grow
in this mouse, and thus the investigator had a near perpetual source of a
singe type of tumor for study. This led to the development of inbreeding
of mice to generate genetically identical animals for experimental use.
Inbreeding is nothing more than a tool to restrict heterozygosity in an
animal. Most animals cannot be inbred because they fix deleterious re-
cessive mutations which are generally lethal. However, inbred lines have
been generated in a small number of experimental animals, including
mice, rats, guinea pigs, and even rabbits. Mice are by far the easiest
species in which to establish inbred strains. Inbreeding is usually car-
ried out by continual brother/sister mating. Each generation, a single
male and female offspring of a mating is selected for breeding. When
this has been accomplished through 20 generations (luckily, the gesta-
tion time for mice is relatively short so that this can be accomplished
within an investigator's lifetime!), an inbred strain has been developed.
Statistically, this leads to animals that are greater than 99.999% identi-
cal, one to another, the “identical twins” of the mouse world. To be sure
that the animals are genetically pure, breeding laboratories will continue
inbreeding the animals.
Many inbred strains of mice are named after their originator or to
identify the characteristics that were selected during the inbreeding. For
example, BALB/c mice, an albino strain, is named after the Ohio mouse
dealer from which the breeding stock was obtained (Halsey
Ba
gg's
ALB
ino; the “c” is the gene symbol for albinism). The DBA strain of mice
is named for three recessive genes that influence coat color in mice,
dilute, brown, and non-agouti and, in fact, was the first inbred strain pro-
duced. C57BL and C57BR mice were derived from female mouse # 57
from the colony of a mouse breeder, “Miss Abbey Lathrop”, in Granby,
Massachusetts. The early generations of these mice segregated coat
color, and were independently inbred to generate black mice (C57BL)
and brown mice (C57BR).
Individual members of an inbred strain of mice are absolutely identi-
cal in their genetic makeup, and therefore they provide a resource from
which identical animals can be used for studies where variations in ge-
netic background must be avoided. The types of studies that have seen
dramatic advances as a result of the development of inbred strains of
mice include transplantation biology, cancer biology, and immunology,
to name but a few.
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