abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 997
indole requirement simultaneously with acquisition of a histidine requirement (EPHRATI-ELIZUR,
SRINNASAN and ZAMENHOF, Proc. Natl. Acad. Sci. U.S. 47:56, 1961). A similar phenomenon
was found in Serratia (KAPLAN, 2. Vererb. 92:21, 1961).-In the present study, DNA’s from
two such strains (12 and 21) were used to transform the parent histidine+ indole- (nonlinked)
strain. In both cases the transformation to indole+ was accomplished, and with usual yield; this
suggests that in strains 12 and 21 the mutation to histidine- by itself did not suppress indole-,
but was “coupled” with another mutation, which either produced true repair of indole-, or else
an unrelated suppressor of indolc. The nature of this coupling is not clear; it suggests that
various “nonlinked” segments of DNA miolecule may not be mutationally independent.
No reversions to indole+ were observed among IO5 survivors of heating that did not mutate to
histidine-, indicating that the phenomenon is not due to the accidental coincidence of two independent
mutations.
ZIMMERING, S., Indiana University, Bloomington, Ind.: Temperature effects and segregation
in Drosophila mazes.-The sc4-sc8 chromosome lacks most of the proximal heterochromatin including
pairing sites (“collochores” of COOPER) and leads to an appreciable frequency of nullo-Xnullo-Y,
and a higher than normal frequency of XY, gametes from males carrying this X chromosome
and a Y chromosome (GERSHENSON 1940; SANDLER and BRAVER 1954). When males of
the composition ysc4-sc*/sc8-Y are raised at 26°C and 18°C from egg to eclosion, and then tested
at 26”C, the relative frequencies of the four kinds of gametes produced (from large scale experiments)
are, for those raised at 26”C, Xz48.2; Yz21.4; XYz2.0; 0=28.5, and for those raised
at 18”C, X=48.3; Y=42.2; XY=3.5; 0=6.0. The question arises: is the more normal transmission
of the Y chromosome from the experiments at the cooler temperature simply the result
of a greater opportunity for the Y chromosome to pair with and disjoin from the X chromosome
or is its more regular behavior independent of pairing. That the latter interpretation may be
correct is suggested by the finding that from Bar-Stone males of the composition XD,XPYL.YS
and not carrying a free Y chromosome, the component XPYL.YS, which is present as a univalent,
is recovered with virtually normal frequency when such males are raised at 18°C (and tested
at 26°C) despite an approximate 5045% loss of this component when they are raised at 26°C.
The possibility that the latter results are related to the so-called A effect (ZIMMERING 1960;
ZIMMERING and BARBOUR 1961) has been ruled out experimentally. (Supported by N.S,.F. grant
G13568.)