Synapsis, recombination, and meiotic segregation in the mesquite lizard, Sceloporus grammicus, complex. I. Pericentric inversion heteromorphism of the F5 cytotype.

Chromosomal pairing and recombination were analyzed in male specimens of Sceloporus grammicus heterozygous for a large pericentric inversion of macrochromosome 4. Analysis of silver-stained synaptonemal complexes (SCs) in surface-spread nuclei revealed that homologously paired inversion loops were not formed. Synapsis of the inverted segments proceeded directly to nonhomologous straight pairing. In some nuclei, this resulted in a configuration that could not be distinguished from homozygous bivalents of similar size. Examination of Giemsa- and silver-stained diakinetic nuclei indicated that crossing-over was limited to the noninverted (homologous) portion of the heteromorphic bivalent. Analysis of secondary spermatocytes (metaphase II configurations) revealed normal disjunction and balanced segregation of the elements of the heteromorphic bivalent. These observations indicate that the inversion heteromorphism does not lead to the production of unbalanced gametes.