A test for allelism with homozygous cht mouse mated to a homozygous mutant mouse produced 32/32 progeny with a dull grey phenotype, unlike cht or a/a . These results suggested chtl is a new allele of the cht gene that produces a different phenotype from the original cht allele. When two matings of the grey color F1s from the allele test progeny were mated together, however, they produced segregating litters for a total of 10 cht looking mice and 3 normal black a/a mice. The appearance of the black mice means either the two mutations are pseudoalleles or modiefier genes can affect the phenotype expresssion.