PURPOSE. To visualize by direct fluorescent in situ hybridization the entir
e human visual pigment gene array on single X-chromosome fibers and to comp
are the results with values obtained by other molecular techniques.
METHODS. The size of the opsin gene array on the X-chromosome in eight male
subjects was investigated by (i) direct visual in situ hybridization (DIRV
ISH) on elongated DNA fibers; (ii) quantitation of genomic restriction frag
ments after Southern blot hybridization; (iii) quantitation of restriction
fragment length polymorphism after PCR amplification (PCR/RFLP); and (iv) s
izing of NotI fragments by pulsed field gel electrophoresis and Southern bl
ot detection. Each male subject's color vision was assessed by Rayleigh mat
ches on a Nagel Type 1 anomaloscope.
RESULTS. The number of genes resolved by the DIRVISH protocol, which ranges
from 1 to 6, agrees exactly with the gene array sizes obtained in the same
male subjects from pulsed field gel electrophoresis, but differs from the
estimates derived from the commonly used indirect Southern blot hybridizati
on and PCR/RFLP quantitation methods. In particular, the PCR/RFLP method ov
erestimates the copy number in all but the smallest arrays.
CONCLUSIONS. Visualization of the X-chromosome opsin gene array by DIRVISH
provides a new, direct method for obtaining exact copy numbers and helps to
resolve the controversy about the range and the average visual pigment gen
e number in the human population in favor of smaller average array sizes.