Single-Locus Inheritance in the Tetraploid Treefrog Hyla versicolor with an Analysis of Expected Progeny Ratios in Tetraploid Organisms.

The recently evolved autotetraploid frog, Hyla versicolor , was examined electrophoretically for evidence of genomic restructuring leading to diploidization. Loci were tested against the progeny ratios expected if inheritance was disomic vs. tetrasomic. Two loci (Mpi and Sod-2) appeared to be inherited tetrasomically, one (Mdh-2) appeared to be inherited disomically, and one (Tpi) appeared to be inherited disomically in one family and tetrasomically in another family, when tested conventionally against 1:2:1 and 1:4:1 segregation ratios. The minimum number of progeny required for this type of analysis for codominant alleles is shown to be 92. Progeny resulting from double reduction were observed, and the occurrence of a null allele class at Mpi was noted. A reexamination of expected progeny ratios in tetraploid organisms reveals that tetrasomic inheritance patterns cannot be predicted without adequate knowledge of the amount of crossing-over, the proportion of tetravalents vs. random bivalents that are formed, and the ratio and types of centromere segregation (alternate and adjacent) that occur from tetravalents in the species being studied. However, disomic inheritance can be unambiguously confirmed only by the production of all heteroallelic gametes from homobivalent, symmetrically heterozygous individuals. In addition, a method is described for estimating genecentromere distances using the ratio of progeny genotypes in certain crosses in tetraploid species.