Abstract
DURING the past academic year, in connection with their course in genetics, our medical students were provided with a study guide consisting mainly of questions and problems, together with answers, for use with the textbook1 as a self-teaching device. One of the questions in the study guide stimulated so much discussion (and initially disagreement) among those involved in teaching this part of the course,† and the answer is of sufficient interest in connection with certain disorders that are currently receiving renewed investigative attention,2 3 4 5 6 7 that I chose to share it more widely with colleagues.The question was as follows: Question 7.3 . . .