Figure 3. Diagram representing BCM genotypes of the 3 British families. The wild type L-M opsin gene array is shown at the top of the figure. Grey boxes represent L opsin exons, and white boxes represent M opsin exons. Subscript n represents one or more M opsin genes. The black box represents the Locus Control Region (LCR). The LCR was present without mutation in all three families. The C203R point mutations detected in Family 1 and Family 3 are shown above the corresponding exons. Family 1 has an inactive hybrid gene followed by a second gene in the array. Three possible structures of this second inactive gene are shown in the bracket. Family 2 has a single nonfunctional hybrid gene lacking exon 2. Family 3 has a single inactive hybrid gene.