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10 Karyotype and Chromosomal Organization

Matthew Breen, Rachael Thomas


The genome of the domestic dog (Canis familiaris) is divided into 78 chromosomes, comprising 38 pairs of acrocentric autosomes and 2 metacentric sex chromosomes. Historically, the high degree of morphological similarity shared by many of the autosomes has presented significant challenges to cytogeneticists. Over the past decade, the development of reagents and resources for molecular cytogenetic analyses of the canine genome has played a vital role in the generation of comprehensive and effective genome and comparative maps for the dog. This chapter provides a summary of the molecular cytogenetic studies that have been conducted on the domestic dog, leading to the development of standardized chromosome nomenclature, comparative cytogenetic maps, integrated genome maps, and the anchoring of the canine genome assembly. The application of molecular cytogenetic approaches to the investigation of chromosome aberrations in canine cancers is also discussed.

The chromosome number of the dog, 2n = 78, was first determined from studies of meiotic cells (Minouchi 1928) and later confirmed using cultured lymphocytes (Gustavsson 1964). The diploid karyotype comprises 38 pairs of acrocentric autosomes, a large sub-metacentric X chromosome, and a small metacentric Y chromosome (Fig. 1). At approximately 137 Mb, the largest autosome, dog chromosome 1, is equivalent in size to human chromosomes 9–12, and all but the four largest dog chromosomes are smaller than human chromosome 19. Conventional Giemsa staining of the chromosomes allows precise identification of only the sex chromosomes (due to their size and morphology) and chromosome 1 (by virtue...

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