Genetic Characterization of a new allele of the rabbit group b C(k) allotypes.

An inherited variant (b4(v)) of the rabbit kappa-chain allotype b4 is characterized by the presence of serine in place of alanine at position 121 and leucine in place of glutamine at position 124. The variant was traced through eight generations of a pedigreed rabbit family. Genetic analysis of this trait demonstrated that it is an allele of the other group b allotypes, and recent breedings have produced rabbits homozygous for this light-chain type. Two findings, other than the amino acid sequence differences, distinguish b4(v) from b4 in our colony. First, the level of expression of b4(v) in heterozygous rabbits is less than that of b4. For example, in b4b4(v) rabbits, approximately 30% of the preimmune IgG carries b4(v). In b4(v)b5 animals, 46% of the IgG carries the allotype b5, although in animals of allotype b4b5, 38% of the IgG is b5. Second, retrospective analysis of some litters revealed an abnormally low frequency of b4(v) in male heterozygotes. However, male b4(v)b4(v) homozygotes were found at the expected frequency in prospective crosses between b4(v)b5 rabbits.