Abstract
The chicken karyotype comprises 39 chromosome pairs of which at least 29 are ‘microchromosomes’. Microchromosomes account for about 25% of the genomic DMA, but they are cytologically indistinguishable from one another1. Due to technical limitations there is a strong bias of mapped genes within the chicken genome database ChickGBASE2 towards macrochromosomes 1–6 and Z, with specific assignments to only one microchromosome3,4. Several genes have, however, been assigned to the microchromosome group as a whole3,5–9, demonstrating that these tiny chromosomes do not represent genetically inert DNA. To determine the overall chromosomal distribution of genes, as well as to provide a mapping resource, we prepared a CpG island library from chicken using differential binding to a methyl-CpG binding column before and after de novo methylation10. Surprisingly, we found that chicken CpG islands are highly concentrated on the microchromosomes, whereas macrochromosomes 1–6 are comparatively gene-poor by this assay. Our results raise the possibility that gene density on chicken microchromosomes approaches the maximum value known for vertebrates.
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McQueen, H., Fantes, J., Cross, S. et al. CpG islands of chicken are concentrated on microchromosomes. Nat Genet 12, 321–324 (1996). https://doi.org/10.1038/ng0396-321
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DOI: https://doi.org/10.1038/ng0396-321
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