Retinal dgeneration 4 Rd4

Retinal degeneration 4 (rd4)

It is homozygous lethal and in heterozygotes is always associated with retinal degeneration. In affected mice, the retinal outer nuclear layer begins to reduce at 10 days of age, showing total loss at 6 weeks. Rd4 has not recombined with the inversion in an outcross, suggesting that the Rd4 locus is located very close to or is disrupted by one of the breakpoints of the inversion on Chr. 4, either near the centromere or near the telomere.

FISH analysis narrowed the region in which the breakpoint lies at the distal end of the chromosome, and showed that the proximal breakpoint is in the centromere itself. Therefore, the Rd4 gene must be disrupted by the telomeric breakpoint of the inversion.