abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 963
tances. For genes more than 25 map units from the centromere, mitotic recombination rates rise
linearly with UV dosage. However, for markers less than 15 units from the centromere homo-
zygosis frequencies via mitotic recombination attain saturation at low UV doses. (This work has
been supported by NIH grant #RG-6979.)
HWANG, Y. L., E. SHULT, G. LINDEGREN, and C. C. LINDEGREN, Southern Illinois University,
Carbondale, Ill.: The chromosome maps of Saccharomyces.-The chromosome maps of Saccharomyces
have been recently extended and new relationships of centromeres, sites of affinity and
gene loci have been demonstrated by hybridizing cultures from a variety of sources including
mutants from Japan, Italy, and California.-The map of Saccharomyces shows ten centromeres,
four sites of affinity and four linkage groups not assigned to known centromeres or affinity sites.
One of the ten centromeres specified by the centromere marker met3 is newly identified. Three
of the affinity sites exhibit preferential segregation with chromosome V, and the fourth affinity
site shows nonrandom assortment with chromosome VIII. Twentytwo gene loci have been
newly located. The data previously reported by LINDEGREN, et al., by HAWTHORNE and MORTI-
MER, and by OSHIMA comprise a total of 57 gene loci.
IVES, P. T., and G. R. FINK, Amherst College, Amherst, Mass.: Comparison of translocation
and crossover chromosomes produced by y irradiation of Drosophila males.-Translocations
(Ts) of chromosomes 2 and 3 were derived from days 5 and 6 sperm of Oregon-R/rucuca males
and crossovers from days 9 and 10 sperm, using an exhaustive mating schedule at 25°C after
two kr. Tests showed homozygous lethality in 84 of 102 Ts and in 24 of 105 non-T second
chromosomes also derived from days 5 and 6 sperm. The estimated lethality due to a T is .35
of a lethal for each of its two chromosomes, with 2.7 T lethals to one non-T lethal per chromosome.
In contrast 11 of 141 crossover chromosomes appearing in males and ten of 172 noncmssover
sibling third chromosomes from days 9 and 10 sperm were recessive lethals, the
difference in these two frequencies being nonsignificant (P = .6) .-The lower lethality in
crossovers us. Ts and the absence of a comparable increase in proportion of lethals in crossover
chromosomes support the views that induced crossovers and Ts are genetically different at their
exchange sites (PATTERSON and STONE 1934) and that if both result from induced chromosome
breakage then lethality arises not from this breakage but probably from a position effect of genes
not themselves affected by the irradiation. (Earlier comparable studies were rendered uncritical
by the later discovery of widely divergent induced mutation frequencies at different spermatogenic
stages.) A difference between induced male and normal female crossingover is still ap parent in their very different proportionate chromosomal distributions. (Supported by Contract
No. AT(30-1)2467 from the U.S.A.E.C.)
IYENGAR, SHANTA V., and RACHEL M. BAKER, Louisiana State University, Baton Rouge, La.:
The influence of temperature on the pattern of insemination by Drosophila melanogaster males9
-Three groups of 20 young Drosophila males from each of two different stocks were treated as
follows: group 1, untreated controls; group 2 and 3 males subjected to 36°C and -8°C respectively
for 15 minutes immediately prior to mating. Each male of the first type was placed
with three virgin females for a day and replaced by the second type male for the next 24 hours
after which the females were individualized and transferred to fresh vials daily for ten days.
The total offspring for groups 1, 2, and 3 were respectively 2578, 3419, and 849 indicating
about a 30 percent increase in group 2 and about a 66 percent decrease in group 3. None of
the females in groups 1 or 3 were fertilized by both males, while in group 2, 10.9% were. The
percentage of unfertilized females in groups 1, 2, and 3 were respectively 27.11%, 7.27%, and
71.4%. While a cold “shock” impairs the physical activity and therefore the fertility of the male,
a mild heat “shock” seems to enhance, rather than impair, the fertility of the male due to one
or several of the following: (1) accelerated spermatogenesis, (2) larger number of sperm per
ejaculate, (3) increased motility of the sperm in the male, as well as in the recipient female as