Expression of the Kandiyohi Gene in Triploid Frogs Produced by Nuclear Transplantation.

variant, known as mottled or kandiyohi, occurs in populations of the common A leopard frog, Rana pipiens, in Minnesota and other north-central states (BRECKENRIDGE 1944; WRIGHT and WRIGHT 1949). The kandiyohi frog was described originally as a new species (WEED 1922), but genetic studies (VOLPE 1955) have revealed that it differs from the wild-type frog by a single dominant gene. The kandiyohi gene has been used as a genetic marker in nuclear transplantation studies. When a blastula nucleus containing the kandiyohi gene is transplanted to an enucleated egg obtained from a wild-type frog, it expresses itself in the appearance of the mutant character in the transformed frog (MCKINNELL 1960, 1962). Similar results are obtained in experiments involving the transplantation of nuclei obtained from the spotless (burnsi) mutant frog to enucleated eggs obtained from wild-type individuals ( SIMPSON and MCKINNELL, 1964, in preparation). Polyploid frogs may be produced with the nuclear transplantation procedure (SAMBUICHI 1959; SUBTELNY and BRADT 1960,1963; KAWAMURA and NISHIOKA 1960). Triploid frogs occur among the individuals produced by transplanting diploid blastula nuclei to unfertilized eggs. The triploid condition has been interpreted as resulting from the fusion of a haploid maternal pronucleus with the transplanted diploid nucleus. In the experiments to be described below, diploid blastula nuclei derived from wild-type frogs were transplanted to activated unfertilized eggs obtained from kandiyohi females. The reciprocal transplantation was also performed, i.e., somatic nuclei heterozygous for the kandiyohi gene were transplanted to activated unfertilized eggs obtained from wild-type frogs. The objective of these experiments was to test the ability of the kandiyohi gene to express itself in the presence of two wild-type alleles, and to provide genetic evidence that fusion of the maternal gamete pronucleus with a transplanted diploid nucleus can occur. A preliminary report of this research was presented elsewhere ( MCKINNELL 1963).