ALLELES: cwb+ (wild-type), cwb (mutant).
PHENOTYPE: Two visible manifestations of the mutant are co-inherited. Cataract-webbed deer mice show webbed toes as soon as toes are sufficiently developed, and the webbing involves digits 3=4 or 2=3=4 on the hind foot and 3=4 or 3=4/5 in front with many variations. The syndactyly component, which involves only soft tissues of the toes, is more than 98% penetrant, but variably expressed. The second and third digits of the hind foot are nearly always involved, and syndactyly is much more evident on the hind foot that the front. It is virtually always bilaterally expressed.
Beginning at about three months homozygotes develop lenticular cataracts. About 63% of the known homozygous animals had cataracts by one year of age and an additional 25% exhibited other opthalmic lesions, for a total penetrance of 88%. Although some of the deer mice show developing cataracts by three months of age, more typically they appear between 6 and 12 months, and in a few after one year of age. Prior to manifestations of cataracts, the animals may have eye hemorrages or other opthalmic changes. In some animals the eye condition is unilaterally expressed, but more commonly it is bilateral. There is no strong correlation between the degrees of expression of syndactyly versus onset time or severity of cataracts. SOURCE: About 1960. University of Oregon. The mutation appeared in the laboratory colony of P. maniculatus.
REFERENCE: Anderson and Burns (1979), Burns and Feeney (1975)