Abstract
From a survey of breeding records of the AGUS/Lac rat colony, 1% of animals weaned were found to lack tails. Post-mortem examination of 5 females showed major skeletal and genital abnormalities. Tailless rats were found more often than expected in 4th and 5th litters. A 'threshold' model of inheritance was postulated with an unknown environmental factor 'triggering' the condition.