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Individual variation in size of the human red and green visual pigment gene array
1Department of Molecular Biology and Genetics, Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Purpose:
To determine the size variation of the X-chromosomal human red and green visual pigment gene array in the general population using pulsed field gel electrophoresis and Southern blotting.
Methods:
Peripheral blood lymphocytes were prepared from 67 anonymous males. The cells were embedded in agarose and the genomic DNA digested with restriction enzyme Not I. The resulting DNA fragments were resolved on a contour-clamped homogeneous electric field gel, and the Not I fragment containing the red and green pigment genes was visualized by Southern blot hybridization with a human green pigment cDNA probe.
Results:
In DNA from each male, a single hybridizing fragment was observed in Not I-digested DNA. The lengths of the fragments from different males were observed to vary in steps of approximately 39 kilobases (kb), consistent with earlier studies showing a visual pigment gene repeat unit of 39 kb and a head-to-tail tandem arrangement of the red and green visual pigment genes. In the population studied, the number of repeat units per X-chromosome had a mean of 2.9 and a standard deviation of 0.94.
Conclusions:
The sizes of visual pigment gene arrays observed in this study resemble those determined in earlier studies based on ratios of restriction fragments resolved by conventional gel electrophoresis and visualized by whole genome Southern blotting, but differ significantly from those determined using ratios of fragments obtained by the polymerase chain reaction.