A genetic study of various enzyme polymorphisms in Pleurodeles waltlii (Urodele Amphibian). II. Peptidases: demonstration of sex linkage.

The existence of four peptidases was demonstrated by starch gel electrophoresis in Pleurodeles waltlii: PEP-1, PEP-2, PEP-3, and PEP-4. Peptidases-3 and -4 are monomorphic, and peptidases-1 and -2 are polymorphic. The heredity of the polymorphisms was studied using individuals arising from crosses or of gynogenetic origin. Peptidase-1 is dimeric; its polymorphism depends on a pair of codominant alleles, Pep-1A and Pep-1B, which are situated on the Z and W sex chromosomes, respectively, in close proximity to, or even within, the sex differential segment. As the differential segment is very close to the centromere, the PEP-1 locus therefore also appears to be closely linked to it. Expression of the PEP-1 locus was shown to be independent of the sex hormone environment. This locus is the first case reported in amphibians of an enzyme marker linked to the genetic sex. It allows the sex of PLeurodeles to be determined before they reach sexual maturity. Peptidase-2 is monomeric. Its polymorphism depends on a pair of codominant alleles on an autosomal PEP-2 locus. The high proportion of heterozygous animals in the gynogenetic offspring of females heterozygous for the PEP-2 locus indicates segregation which is independent of the centromere. Analysis of the offspring of doubly heterozygous females (i.e., for two of the loci--LDH-B, G6PDH, PEP-1, and PEP-2) shows that the four loci are independent.