THE IDIOGRAM OF THE SHEEP WITH PARTICULAR REFERENCE TO SECONDARY CONSTRICTIONS

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Abstract
Peripheral leukocyte cultures from 22 normal sheep less than 2 years old showed that the modal diploid chromosome number (54) was present in 87.44% of cells counted from a total of 1831. The modal number of 54 chromosomes is verified for 5 previously unreported breeds of sheep, including the Scottish Blackface, Grey Face, Clun Forest, Welsh Mountain and Soay. Karyotype observations showed that the short arms of the X-chromosome are noticeably larger than those on other members of the acrocentric group of chromosomes, and that the Y-chromosome is clearly submetacentric. Secondary constrictions were seen on a number of the 333 "photographic" karyotypes prepared from the best metaphases of 3280 counted cells. The incidence of these was highest on the 6 large metacentric chromosomes and suggested sites of regular occurrence, which may be associated with nucleolus formation. An increase in the incidence of secondary constrictions was recorded in preparations made from cultures in which hypotonic Na-citrate was used instead of hypotonic Hanks balanced salt solution.

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