abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 95 7
tion, respectively, produced by the addition of a Y chromosome to the various inversion hetero-
zygotes is as follows: sc7/+ (26.3, -16.2), BM'/+ (18.5, +10.8), 65/+ (25.9, -9.7), AB/+
(29.3, +M.5), dl-M/+ (50.6, -25.3), scS/+ (19.2, f37.3). Since the effect of the Y on cross-
ing-over is not correlated with its effect on disjunction, but depends on the location of the X-in-
version, it is proposed that associations between the X and Y, that lead to exceptions, occur sub-
sequent to exchange at distributiue pairing, and that they involve only those X chromosomes
that have not participated in exchange with each other.
HARDON, JAAP J., University of California, Davis, California: Self-incompatibility and selfcompatibility
in Solanum pennellii Cor. in relation to its unilateral compatibility with Lycopersicon
esculentum Mill.-Self-incompatibility (SI) controlled gametophytically by S alleles at one
locus has been discovered in two accessions (hereafter designated as SI S.P.) of Solanum pennellii.
The original living accession (SF S.P.) is completely self-fertile (SF). Pollen tubes of
incompatible matings cease growth in the uppermost 3 mm of styles. All three collections can be
hybridized with Lycopersicon esculentum but only with the latter as female parent. All individuals
of F, and F, L. esculentum x SI S.p. exhibit the strict SI of the pennellii parent. Each
F, consists of two intercompatible classes. In all preceding aspects the behavior is the same as
that of hybrids between L. esculentum and SI species of Lycopersicon. F, L. esculentum x SF
S.p. is self-fertile and a backcross to SI S.p. segregated approximately 1 SI: 1 SF. These and other
results support LEWIS and CROWE'S (1958) model of stepwise mutation leading from SI (as in
SI S.P.) via intermediate SF (as in SF S.P.) to SF (as in L. esculentum).-The following facts
bear on the relationship with unilateral crossing behavior. No plants of F, or F, L. esculentum x
SI S.p. were compatible as staminate parents with any SI S.p. nor as pistillate parents with L.
esculentum. The first backcross (30 plants) of the same hybrid to SI S.p. behaved in the same
fashion. The results suggest that the unilateral barrier is regulated to some extent by SI but also
by additional, perhaps polygenic, control. (Support by grant G-10704 of the National Science
Foundation is acknowledged.)
HAWTHORNE, D. C., University of Washington, Seattle, Wash.: Supersuppressors in yeast.-
Cases are known in Drosophila, Neurospora, and bacteria in which the effects of mutant genes
at two or more loci are suppressed by a single suppressor gene. In yeast, Saccharomyces cereuisiae,
several supersuppressors have been found, each with a nearly identical action spectrum
which includes mutants for adenine, arginine, histidine, isoleucine, leucine, lysine, tryptophane,
tyrosine, and uracil requirements and a genetic petite condition. Although not locus specific,
therefore, the suppressors are specific in that they will restore to normal or near-normal the
mutant character associated with only a fraction of the different heteroalleles at a given locus.
Altogether the super-suppressors suppress the phenotypic expression of about one fourth of all
the genes examined. Because of the frequency as well as the diversity of the suppressible mutants
it is thought that these mutants might well represent a class of enzyme aberrations which
would respond to some slight change in the physiology of the cell caused by the suppressor gene.
HECHT,
A., Washington State University, Pullman, Wash.: Znactiuation of an incompatibility
substance by means of high temperature treatments.-Under normal field growing conditions
as well as under similar conditions in the laboratory it has been observed that pollen tubes of
Oenothera organensis do not even enter the tissues of stigmas which have been self-pollinated.
Pollination with genetically compatible pollen results in the germination of many more of the
pollen grains and their easy penetration into the tissues of the stigma and style. Earlier experi-
ments involving stylar grafts have indicated that the inhibition of the incompatible pollen oc-
curs both in stigma and style, but that the reaction is strongest in the stigma.-If styles are ex-
cised at their junction with the ovary, and are then treated at temperatures just below what will
kill their sells (5Oo-57"C), some change occurs reducing the intensity of the incompatibility
reaction: after approximately five minutes at this temperature, whether the styles are immersed