abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 959
found in meiotic stages; among these, 91 had a single sperm, two had two sperms, and three
had no visible sperm. Among 127 eggs of D. virilis, 87 eggs had a single sperm, no sperm was
visible in 40 eggs, and no case of polyspermy was observed. The possibility was investigated
that soon after their alleged entry into the egg, the supernumerary sperms undergo some
degenerative change which prevents their detection with the Feulgen technique. Drosophila
melanogaster eggs, fertilized by H3-thymidine labeled sperms, were collected; these eggs were
sectioned, stained with Feulgen or Azur-eosin Giemsa, and processed for autoradiography. At
the time of writing of the abstract, 40 eggs have been examined; the autoradiographic data
also indicate that polyspermy is a rare event in D. melanogaster. (Research performed under
the auspices of the U.S. Atomic Energy Commission.)
HINTON, C. W., University of Georgia, Athens, Georgia: Another interchromosomal effect
on crossing-over in Drosophila meLanogaster.-The mutant c3G, when homozygous, virtually
eliminates crossing-over. It has been found that the third chromosome bearing this mutant
exerts, when heterozygous, an interchromosomal effect on crossing-over comparable in magni-
tude to that of the multiply inverted chromosomes Ubx and SM5. Analysis of T-point X
chromosome testcross data (N = 10676) from females of the genotypes +/+, +/c3G, +/Ubx
and c3G/Ubx shows that while regional responses to +/c3G and +/Ubx are quantitatively
different, their combined effects are approximately additive for five of the six regions. Tetrad
analysis suggests no significant differences between the effects of the c3G and Ubx chromosomes;
double and triple exchange frequencies are increased in both cases. Similar relations are indi-
cated for c3G and SM5 in less extensive data.-That this effect of the c3G chromosome is not
itself due to a rearrangement is shown by its presence intrachromosomally and by apparently
normal salivaries. Whether the effect is a property of the c3G mutant remains to be determined.
(Supported by grant C-3000 from the National Institutes of Health.)
HOCHMAN, B., University of Utah, Salt Lake City, Utah: Further investigation of fourth
chromosomes from natural populations of Drosophila m1anogaster.-An earlier analysis of 104
fourth chromosomes removed in October, 1960, from a wild population of D. melanogaster in
Tennessee, revealed three containing recessive lethal genes. These microchromosomal lethals,
the first detected outside the laboratory, proved nonallelic inter se but two were identical to
two different lethals of X-ray origin and the third interacted lethally with bent-Dominant, a
chromosome IV dominant visible-recessive lethal.-Sampling on an enlarged scale the following
year (at sites in Tennessee, Utah and Massachusetts) has uncovered six additional lethalbearing
fourth chromosomes out of some MO examined. Two of these six are allelic. The results
of attempts to localize all of the lethals, as well as the classification of the nonlethal chromosomes
with respect to viability will be reported.-The following tentative conclusions seem warranted:
(1) Microchromosomally based lethals may be carried in gene pools of wild populations at
frequencies higher than expected considering the paucity of loci in this autosome. (2) Different
populations may be characterized by rather dissimilar frequencies of these lethals (2-3 percent
in two Tennessee populations as compared to 0.5 percent at the Utah site). (3) In contrast to
what is found in the larger autosomes, very few (< 10%) of the lethal-free fourth chromosomes
carry factors which depress the viability of homozygotes below the normal range.
HORIUCHI, T., S. HORIUCHI, and A. NOMCK, University of Oregon, Eugene, Ore.: A heatsensitive
regulatory system.-A variant of the K-12 strain of E. coli called E103 has been
obtained which to a first approximation behaves like an inducible strain for P-galactosidaseformation
at lower temperatures of incubation, and like a constitutive strain at higher temperatures
(HORIUCHI, HORIUCHI and NOVICK, J. Mol. Biol. 3: 703, 1961). p-galactosidase extracted
from E103 is similar in Michaelis Constant and heat sensitivity to the enzyme of normal strains.
The operator gene (JACOB and MONOD, J. Mol. Biol. 3:318, 1961) of this strain is normal, showing
repressibility in heterogenic cells containing a normal regulator gene. The result of an