M Demerec
1938 Genetics  
Institution of Washington, Providence, R. I. : Maternal ejects in Cladocera. -On analysis three independent groups of data show results readily explicable as maternal effects. Sex intergradedness and excavated head in Daphnia longispina are characters highly variable in their phenotypic expression within a clone. (I) The average degree of sex intergradedness of offspring from high mothers of a clone is nearly the same as that for simultaneously reared offspring of low mothers of the same clone;
more » ... of the same clone; but in each of the series tested the high mothers had a slightly higher average expression of sex intergradedness in their offspring than did the low mothers. (2) In certain of the selection experiments involving the excavated head character the high selections for a long period of parthenogenetic generations produced offspring which had means slightly but consistently above the corresponding means for the low selected line of the same clone; yet these differences were apparently nongenetic. These significant data, obtained late in the selection experiments, seem highly reliable. (3) In sexual reproduction, 9 from sex intergrade clone by d from normal clone, as compared with the reciprocal cross ( 9 normal by d sex intergrade), produced offspring clones averaging higher in their expression of sex intergradedness. The same applies to reciprocal crosses of excavated head by normal. BELGOVSKY, M. L., and MULLER, H. J., Institute of Genetics of the Academy of Sciences of the U.S.S.R., Moscow, U.S.S.R.: Further evidence of the prevalence of minute rearrangement and absence of simple breakage in and near chromocentral regions, and its bearing on the mechanisms of mosaicism and rearrangement.-Other X chromosomes constituted like scute-8, for example scute-SI, give similar results. I n Bar-M2, having an interstitial chromocentral region slightly proximal to forked, absence of simple breaks :is phenotypically evident, but irradiation produces comparatively many forked "mutations," often with lethals, mosaicism, etc., illustrating predisposition of chromocentral and any adjoining regions to compound breakage with minute rearrangement. -Supposing the spontaneous tendency to such rearrangement intensified in somatic cells, these results lead to interpretation of "eversporting displacements,' essentially like SCHULTZ'S recent interpretation based on his salivary finding of minute deletions. (Conceivably, additional chromocentral sections,
doi:10.1093/genetics/23.1.139 fatcat:oziqqnf6jfbc5ffmhy4dd2q5ty