The Jackson Laboratory

The recessively inherited cocoa 7 Jackson (Hps3^coa-7J) mutation arose spontaneously in a colony of C3H/HeJ mice in the Russell-Dickie Foundation Stocks colonies at The Jackson Laboratory and was discover by Helen Tracey in 2004. Like previously described Hps3^coa mutants, mice homozygous for the coa^7J mutation have a lighter coat color than littermate controls (See Photo) and can be recognized when their first coat of hair comes in at about 10 days of age. The originally described coa mutants had prolonged bleeding associated with a platelet defect. Bloodwork was not performed on the coa^7J mutants, so it is uncertain that they carry the platelet defect. Heterozygotes have a normal C3H/HeJ coat color (agouti). Both homozygotes and heterozygotes breed well and live a normal lifespan.

Genetic Analysis

Using our standard mapping protocols a linkage cross was performed by mating a CAST/Ei male mouse to a female homozygous for the coa^7J mutation. F1 progeny from this mating were intercrossed and produced 54 affected animals of which 21 were used for linkage analysis. The mutation was mapped to the region of Chromosome 3 where the Hps3^coa gene is located. Because of the similarity of phenotype of Hps3^coa mutants to the new mutation, a test for allelism was performed. A homozygous mutant female B6.B10-Hps3^coa/J mouse was mated to a male heterozygous for this new coa^7J mutation. In two litters, 16 progeny were produced of which 7 were affected with the coa phenotype proving allelism.

Acknowledgements

We wish to thank Helen Tracey for identification of the Hps3^coa7J mice and Jane Maynard for  linkage cross tissue preparation.