Influence of Certain Color Mutations on Body Size in Mice, Rats, and Rabbits.

HIS paper is a further contribution to a series of studies on size inT heritance in mice begun some years ago a t the Bussey Institution of Harvard University by my colleagues and myself and designed to throw light on the question how particular mutant genes affect the growth of the body and so influence adult body size. In previous studies it was found that the gene for brown pigmentation and the gene for dilute pigmentation accelerate growth and thus increase adult body size, as judged by criteria of body weight, body length, and tail length. By like criteria it has been found that the gene for short-ear and the gene for pink-eye decrease adult body size, but that the gene for agouti and the gene for complete albinism are neutral, neither increasing nor decreasing body size. The present study is concerned with the influence on body size of three other mutant genes, leaden, pink-eye 2, and yellow. Leaden is phenotypically similar to blue dilution, and pink-eye 2 is phenotypically similar to ordinary pink-eye, but both are entirely distinct genetically from the better known mutants which they resemble. Leaden, unlike blue dilution, has a retarding influence on growth, and pink-eye 2 has a stronger retarding effect than ordinary pink-eye, as will presently appear. Yellow, as is well known, has a lethal effect when homozygous but increases body size when heterozygous. This paper deals also with a further study of the influence of the brown mutation on body size, the investigation being extended from mice to rats and rabbits also.