Physiological Aspects of Genetics

While recognizing that all of genetics must have a physiological basis--and ultimately a physico-chemical one-geneticists for many years have been concerned largely with the numerical and geometrical aspects of heredity. Within recent years, however there has been an evident and growing interest in problems that have to do with the relation of hereditary mechanisms and hereditary units to other branches of biology. A surprisingly large number of specific physiological reactions are now known to be under the control of genes. As an example, Trimble & Keeler have verified and extended earlier observations on differences in nitrogen metabolism in dogs. Most breeds of dogs excrete only a small amount of uric acid (0.2 to 0.4 per cent of the total urinary nitrogen). Individuals of the Dalmatian breed, however, excrete less nitrogen as allantoin and more as uric acid (2 to 3 per cent of the total nitrogen). Trimble & Keeler have verified the earlier suggestion of Onslow that high uric acid excretion is differentiated from low uric acid excretion by a single recessive gene. The geneticist is, in fact, confident that all processes characteristic of living organisms are ultimately gene-controlled.