CHROMOSOMAL VARIATION IN THE PLAINS WOODRAT: GEOGRAPHICAL DISTRIBUTION OF THREE CHROMOSOMAL MORPHS.

Abstract

Neotoma micropus ranges over most of the western two-thirds of Texas, the northeastern corner of Mexico, most of New Mexico, and parts of Colorado, Kansas, and Oklahoma (Hall and Kelson, 1959). An extensive chromosomal polymorphism has been reported in this species (Baker and Mascarello, 1969; Baker et al., 1970). Using regular karyotypic techniques (without banding), this polymorphism was found to consist of variation in the morphology of one pair of large autosomes. The morphology of this pair varied as follows: (1) both as acrocentrics (Morph I), (2) one as an acrocentric, the other a larger submetacentric (Morph II), or (3) both as large submetacentrics (Morph III). Mascarello and Warner (1974) examined C-band and G-band preparations from seventeen specimens of N. micropus and found that both an inversion and deletion within a block of constitutive heterochromatin are responsible for this polymorphism. Banded preparations showed the system to be a bit more complex than that described above. In fact, a fourth type of chromosome arrangement was noted in which there were two biarmed chromosomes. However, one (a subtelocentric) had a distinctly shorter second arm than the other (a submetacentric). None of the banded preparations were found to be homozygous for the subtelocentric condition. In addition to not being visible in regular karotypic preparations, the very short