W. S. Murray
1927 Science  
Since Johannsen (1903) (2) first expounded his theory of "pure lines " in genetic problems, investigators in all branches of this type of research have come to realize the importance of having stocks of plants or of animals, the genetic constitutions of the individual members of which are as homogeneous as it is possible to make them. I n plants the procedure followed in the establishing of such a homogeneous race is relatively simple, the ovum of the plant being fertilized by pollen from the
more » ... y pollen from the same individual. In higher animals the process becomes more difficult since self-fertilization is not possible. The process followed by animal geneticists in the production of pure lines is known as inbreeding. The more common forms of this technic are: (1) the mating of brothers and sisters, (2) the back-crossing of the young animals to their fathers and mothers. By the continuous use of these methods a line can be made practically homogeneous in from fifteen to twenty generations. The race of mice which has been used in the present experiment is the result of such a homologizing process. Starting in 1909 with a single pair, this line has been developed by Dr. Little to the present time, by brother to sister matings for the most part, and occasionally a back-cross mating. In some of the later generations close cousins have been mated.' Contrary to prevailing opinion in regard to inbreeding, such a process does not have a deteriorating effect upon the descendants of these animals, the colony today being as virile and vigorous as any of the less closely bred stocks in the laboratory.
doi:10.1126/science.66.1720.600 pmid:17810393 fatcat:vyn6cllpd5cxxemso45gahql6q