The Number of Genes Controlling the Response of Chick Embryo Chorioallantoic Membranes to Tumor Induction by Rous Sarcoma Virus.

WO previous workers have estimated the number of pairs of genes controlling Tthe response of the chicken to Rous sarcoma virus. PRINCE (1958) proposed (a) that a single pair of autosomal alleles controlled susceptibility and resistance of chorioallantoic membranes to Rous sarcoma virus and (b) that susceptibility (allele S) was dominant to resistance (s) . This proposal was based on the proportion of nonreacting chorioallantoic membranes in the Pure Hope White Leghorn strain and the Fayoumi strain, and in their reciprocal crosses. Assuming one pair of autosomal alleles, in which susceptibility was dominant to resistance, the product of the gene frequencies of the recessive gene (s) in the two parental strains would give the proportion of the nonreacting chorioallantoic membranes in the reciprocal crosses. This calculated proportion of nonreacting membranes was found to approximate closely the observed proportion. WATERS and BURMESTER (1961) reported that a single pair of alleles was responsible for susceptibility and resistance of the day-old chick to intracerebral inoculations of Rous sarcoma virus. Progeny from five unrelated inbred lines, and their reciprocal crosses, were challenged with this virus. Susceptibility appeared dominant to resistance, because 100% mortality occurred among the reciprocal inbred-cross progeny from certain crosses between resistant and susceptible lines of chickens. A supposedly heterozygous sire (8s) mated to resistant dams (ss) gave full-sib families, each with a ratio of resistant to susceptible progeny closely approximating 1 : 1. The same sire mated to supposedly heterozygous dams (8s) gave 3:l ratios of susceptible to resistant progeny. DHALIWAL (1963) in a study of the mode of inheritance of resistance of the chorioallantoic membrane to inoculation with Rous sarcoma virus stated that resistance was dominant to susceptibility. However, it could not be determined from his results whether resistance was due to a single gene or number of genes. CRITTENDEN, AKAZAKI and REAMER (1963) found that the genetic response of chorioallantoic membranes (CAMS) of chick embryos to Rous sarcoma virus (RSV) was similar to that of tissue cultures of embryos to this virus. In both