Polygenic Control of the Teratogenicity

ROSOPHILA, chickens and mammals have frequently shown interstrain differences in the reactions of their embryos to teratogenic agents. In those cases in which such differences have been investigated, the data have been interpreted as demonstrating a polygenic basis for inheritance, but so far as we are aware, no attempts have been made to estimate the number of genes nor the contributions by individual genes. In Drosophila, interstrain differences in developmental responses to teratogens have been reported for heat shock (GOLDSCHMIDT 1935), sodium metaborate (SANG and MCDONALD 1954) and sodium tetraborate ( GOLDSCHMIDT and PITERWICK 1956, 1957a, b) . GOLDSCHMIDT and PITERNICK (195713) made crosses between Drosophila stocks of different reactivity and discovered that many, but not all, of the specific responses of both parents appeared in the hybrids. Although the experiments were not quantitative, it was concluded that some of the typical reactions of individual lines were dominant. In some of the noninbred Drosophila stocks, selection for frequency of response to sodium teraborate was possible, and the investigators suggested that a multifactorial modifier system plus a simple, perhaps monofactorial, main difference might have been the genetic bases for the selection ( GOLDSCHMIDT and PITERNICK 1956, 1957a). Also, selection has been successful within noninbred Drosophila stocks for lines sensitive and resistant to the development of a break in the posterior crossvein induced by heat shock (WADDINGTON 1953) and for lines with high and low frequencies of a bithoraxlike phenocopy produced by ether vapor (WADDINGTON 1956). In both reports, WADDINGTON concluded that many loci were involved. LANDAUER (1948, 1957, 1958, 1960) has reviewed his extensive investigations on the effects of teratogenic agents on chicken embryos. Differences were found between strains, or between stocks within a strain, in the reactions of their embryos to insulin, boric acid, ethyl carbamate, thallium, and nicotine sulfate and physostigmine sulfate. By selection, lines were isolated with either high or low frequencies of certain abnormalities induced by insulin. The genetic basis for the interand intrastrain differences and for the differential responses after selection was concluded to be multifactorial. In mammals, interstrain differences in frequencies of developmental abnormalities have been shown for a variety of teratogenic conditions. Unfortunately,