Females heterozygous for congenital colour vision defects are of inter
est because they are believed to have cone photoreceptor ratios and co
ne photopigments that differ from normal. We describe a molecular gene
tic method to identify protan carriers that involves characterizing th
e genes that occur in the most upstream position in each of the X-chro
mosome photopigment gene arrays. (C) 1998 Elsevier Science Ltd. All ri
ghts reserved.