a1 A.R.C. Unit of Animal Genetics, Institute of Animal Genetics, Edinburgh
1. Some characteristics are described of 10 steer progeny of a Friesian bull which is known to have carried the factor for muscular hypertrophy.
2. On average these steers had a higher birth weight, lighter hide and liver, smaller feet and cannon bones, a lower percentage of fat and higher percentage of lean in the 10th rib joint, than the progeny of three other Friesian bulls reared at the same time and under the same conditions.
3. No one character was an adequate criterion for separating affected from normal progeny. It appears possible that the bull concerned was homozygous for the double muscling gene, and that all his progeny showed one or more symptoms of the condition.
(Received June 19 1962)