Mark, His Sister and the Scientists

Mark is anchored to a wheelchair by a crippling inherited disease, Duchenne's muscular dystrophy. His sister, Tracey, is not affected, but she could be a carrier - in danger of passing the disease on to any male babies she may have. The scientists, led by Kay Davies , are struggling to develop a test that will tell Tracey whether she is a carrier or whether she is lucky and can forget her fears.