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A revision of the standardized karyotype of deer mice (Peromyscus) is presented. This revision addresses shortcomings of the original standardization, contains a substantial increase in the number of G-band markers and provides a nomenclature for the G-bands of each autosome and the X chromosome. Using the revised standardized karyotype, we specify the particular G-bands or patterns that identify each chromosome and catalog the more problematic chromosome identifications and likely misidentifications. For each chromosome, we present an overview of previously reported variation in euchromatic arrangement and heterochromatic constitution. We then review previous applications of the standardized karyotype and summarize the predominant findings from cytogenetic and cytosystematic studies of Peromyscus and related taxa.

Karyotypic data from 561 deer mice (Peromyscus spp.) from populations on islands off British Columbia and Washington indicate the presence of two distinct karyotypic groups, a low fundamental number (FN) group (FN = 74–78) and a high FN group (FN = 85–92). The absence of karyotypic intermediates at nine localities of sympatry is interpreted as demonstrating that the two FN groups represent distinct species. Based on data from comparable mainland forms, the low FN form is considered to represent Peromyscus maniculatus and the high FN form is suggested to be conspecific with Peromyscus areas. Chromosomal banding data indicate extensive chromosomal variation within each of these species and provide discrete karyotypic characters unique to each species. The inclusion of the high FN insular forms with P. oreas does not affect the chromosomally determined cladistic placement of P. oreas as a laxon derived from P. maniculatus.

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