abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 983
enzyme synthesis.-Five alleles of the E gene, E", EL, EN, ER, and ES, specify five electropho-
retically distinguishable forms of the pH 7.5 esterase enzyme in maize and teosinte. This en-
zyme is found in the developing endosperm as well as in the developing embryo, seedling and
plant tissue. Two new mutants designated E"' and Est are indistinguishable from EF and E" in
their behavior in the diploid tissue, but in the endosperm are characterized by a precocious sus-
pension of gene action. The activity of EF' is cut off earlier than ES'. In heterozygotes with a nor-
mal-acting allele, as for example EF'/EF'/EN, both alleles are equally active in the young endo-
sperm (14 days after pollination) and three enzyme bands are observed in zone electrophoresis,
intense FF and FN hybrid, and a weak NN. By 20 days after pollination the EF' allele is com-
pletely inactive while the EN allele still shows full activity and only a single esterase type, NN,
is present in the endosperm. These regulatory mutants involve alterations at or close to the site of
the structural gene since no recombinations have been found in more than 2500 endosperms
tested.
SEARS, E. R., U. S. Department of Agriculture and University of Missouri, Columbia, MO.:
The use of telocentric chromosomes in linkage mapping.-Telocentric chromosomes, which are
readily obtainable in common wheat through misdivision of monosomes, not only permit the assignment
of genes to particular chromosome arms but also make possible the determination of
gene-centromere distances. For example, the long arm of chromosome 6B carries the awn inhibitor
B,. To determine the distance of B, from the centromere, a telocentric carrying B, was
combined with a normal chromosome carrying b,. When the plants concerned were used as
males in a testcross, only six of 231 offspring had B,. Two of these six possessed the paternal
telocentric and were thus noncrossovers, and three had both paternal chromosomes and therefore
could not be scored. Thus crossing-over between B, and the centromere was only 1/228 or
O.M%. In the same experiment another gene on this arm, Sr,, (stem-rust resistance from the
variety Timstein), showed M.3 2 3.2% recombination with the centromere. In a second experiment
presence of a marker on the short (nucleolar) arm of the normal 6B allowed use of the
heterozygote as the female, and presence of a gene a few units proximal to Sr,, permitted
detection of some of the double crossovers. Here crossing-over between Sr,, and the centromere
was 49/98 or 50%. The gene proximal to Sr,,, pollen-killer (Ki), showed 9.2 *2.9% recombination
with Sr,,. In this and a third experiment not involving Sr,,, recombination between
Ki and the centromere was 43.1% 2 3,5%.-Neatby's virescent (U) on chromosome 3B showed
only 0.29% recombination with the centromere in 350 gametes tested.
SEECOF, R. L., Calif. Institute of Technology, Pasadena, Calif.: Treatment of eggs from carbon
dioxide sensitive Drosophila with X-rays and ultrauiolet radiation.-Eggs were collected from
females of a stabilized, carbon dioxide sensitive strain of Drosophila melanogaster, irradiated with
X-rays or ultraviolet light, and permitted to develop into adult flies. The titer of the virus-like
factor (sigma factor) causing the sensitivity was measured in these adults and compared to the
titer in adults that developed from untreated eggs. Ultraviolet radiation from a germicidal lamp
in doses of 2.00-600 ergs/mm2 (mortality 154%) caused 4-8-fold increases in titer. Higher
doses were not effective in raising titers. X-ray treatments in a range giving u)-70% mortality
failed to cause measurable changes in titer. The titer increases following ultraviolet light treatment
were significant in all of the three experiments done to date, but more elaborate control
experiments are needed to establish the effect. Experiments are now being done to confirm the
titer increases and to determine whether the titer increases represent an induction of infectious
sigma from a noninfectious stage in the sigma life cycle.
SHAMA RAO, H. K., and E. R. SEARS, Atomic Energy Estab., Trombay, India, and U.S. Department
of Agriculture, Columbia, MO.: EMS-induced mutations in hexaploid wheat.-Seeds of
normal Chinese Spring wheat and of monosomics 2B and 6B of this variety at 12% moisture
were soaked in 0.05 M ethyl methanesulfonate at 30°C for six hours, a treatment which permitted