‘Wall eye’—partial or total discoloration of the iris—is known to occur frequently but not constantly in dappled dachshunds, merled collies, and other merled breeds of dog. Observations are recorded on the dappled dachshund, the merled collie, and the merled miniature collie, showing that in contrast to the inconstant iris anomaly the tapetum of such animals is always anomalous. It is generally totally lacking and when present it is rudimentary. The anomalies of the tapetum are easily observed with the ophthalmoscope.
It is known that the dappled or merled animal is heterozygous, and it has been suggested that there is a geneM responsible for merling. Evidence is brought forward to show that the gene is intermediate in effect, independent from the allelic series for coat colour, autosomal in location, and productive of gross ocular anomalies in the homozygote, which also shows marked depigmentation of the coat and frequently deafness as well. In the simplex state the gene is therefore productive of ‘physiological’ variations, whilst in the duplex state its effects are pathological.
Attention is drawn to somewhat similar occurrences in the great Dane, and to the possibility that a gene of this type is widely distributed over different species. The relationship of the appearances seen in the dog to the syndrome described by Waardenburg in man is discussed.
We are indebted to Miss M. Hill of West Haddon, Mrs V. Ripley of Weekley, Miss K. M. Raine of Dartford, Miss W. Riley of Torquay, and Miss M. E. Osborne of Harrietsham for their co-operation and help.
Volume 100, 2021
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