Summary
The finding of heteromorphisms in certain regions of human chromosomes is useful in chromosome identification, especially in the study of the origin of nondisjunction. Quantitation of heteromorphisms in the smaller human chromosomes is theoretically valuable but remains technically difficult. In this paper we evaluate two methods for quantitation of human chromosome 21—visual and densitometric measurement of Q-banded 35-mm negatives. Thirteen parameters are defined for chromosome 21. We find three of them to show less variability between different measurements of the same cell and from cell to cell in the same individual: (1) the centromere index, defined as the ratio of length of the satellite, stalk, and short arm to the length of the satellite, stalk, and short and long arms; (2) the ratio of length of the satellite to the length of the total heteromorphic region of the short arm; and (3) the ratio of the short arm intensity to the intensity of band q21. Another parameter, the ratio of satellite intensity to the intensity of band q21, is reproducible by visual measurement but not by densitometry. Based on these studies we conclude that densitometry is not necessarily better than visual quantitation of the heteromorphic region of chromosome 21.
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Yu, C.W., Downey, H.M. & Priest, J.H. Densitometric and visual measurements of human chromosome 21. Hum Genet 53, 149–153 (1980). https://doi.org/10.1007/BF00273486
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DOI: https://doi.org/10.1007/BF00273486