Genetic Characterization of a new allele of the rabbit group b Ck allotypes

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Abstract
An inherited variant (b4v) 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 b4v from b4 in our colony. First, the level of expression of b4v in heterozygous rabbits is less than that of b4. For example, in b4b4v rabbits, approximately 30% of the preimmune IgG carries b4v. In b4vb5 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 b4v in male heterozygotes. However, male b4vb4v homozygotes were found at the expected frequency in prospective crosses between b4vb5 rabbits.