abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 94 7
development of corn pollen show large differences in the number and type of endosperm muta-
tions recovered. The most sensitive stage for induced loss of endosperm markers is five days
before the pollen is shed. This probably corresponds to the prophase of the second pollen mitosis.
One thousand roentgens of gamma radiation given at the rate of 46r/hr at this stage produces
twice as many losses of marker genes (120 x 10-4) as that delivered at either four or six days
before pollen shedding. This five day rate is ten times that of mature pollen (radiated 0, 1, 2, or
3 days before shedding). The genes CZ Sh Bz and Wz in chromosome 9 were studied. Most of
the losses induced involve large rearrangements of chromosomes. Only six percent of the mu-
tations involve the loss of but one gene in chromosome 9, one percent the loss of two genes,
20% the loss of three genes, and 73% the loss of all four genes being studied. The chromosomal
type losses begin increasing at about 15 days before pollination. Chromosomal losses from radi-
ation given earlier than 15 days before pollination are about twice the control rate and at five
days are about 100 times the control. Eleven mutations for single genes which showed no
evidence of sterility have been recovered from radiation given between 19 and 13 days before
mature pollen. These were most likely induced after meiosis and before the first pollen mitosis.
We have also recovered four “gene” type mutations from material radiated before meiosis. One
thousand roentgens of gamma radiation given at the rate of Mr/hr during these stages produced
shrunken “gene” type mutants at the rate of 53 x 10-6. The control rate is about 2 x 10-6.
CENTER, E. M., Stanford University School of Medicine, Stanford, California: A comparison
of some teratogenic effects in mice.-Since finding that nitrogen mustard (HN, form) is
effective as a teratogenic agent (DANFORTH and CENTER, Proc. Soc. Exptl. Biol. Med. 86:
705, 1954) other chemicals have been investigated in this regard. Beyond a few vascular
changes, it is doubtful that any definite morphological abnormalities occurred among a
limited number of embryos treated in utero with Feulgen solution. Following propyl-thiouracil
treatment of 35 pregnant females, it was also difficult except in five litters to estimate whether
any definite effects were resultant. In comparison with HN, this is seemingly a relatively ineffective
agent.-Recently, experiments were begun with nitrosoguanidine, this chemical is, like
HN,, reasonably efficient at inducing abnormalities. Perhaps this can be best indicated by comparkg
the results of these two agents. Although it should be emphasized that strain differences
in response and variations in severity of treatment may call for some qualification of comparative
statements, it seems evident that nitrosoguanidine has a more pronounced effect on the
earlier embryonic stages of seven, eight, and nine days than HN,. On the other hand, of the two,
HN, has an apparently greater effect on developing embryos on days 13, 14, and 15. While
effects resulting from both chemicals include edema, vascular changes, eye defects, abnormal
tails, and digital abnormalities, nitrosoguanidine tends to reduce in size all elements of the foot
whereas HN, tends to suppress completely the development of one or more individual digits.
CHAPIN, MARGARET,
and G. R. DUBES, University of Kansas School of Medicine, Kansas City,
Kansas: Adenine-resistant mutant of poliovirus.-In 1957 and 1961 we reported cystine-response
(CT) mutants and tryptophan-requiring (tr) mutant of poliovirus, respectively. Now we report
an adenine-resistant (ad) mutant, which was selected by 14 passages, starting with wild-type
Brooks virus, on monkey kidney tissue cultures under medium containing 3 miv adenine, a
concentration strongly inhibiting wild-type virus but not markedly cytotoxic.-Plaque produc-
tion by mutant is slightly inhibited and rate of appearance of progeny virus from it is dimin-
ished slightly by 3 miv adenine; by both these criteria wild type is strongly inhibited. Adeno-
sine (5 mix) and adenosine-5’-phosphoric acid (4 miv) similarly differentiate between mutant
and wild type, though they are less inhibitory than adenine. Neither wild type nor mutant is
inhibited by high concentrations of guanine (1 miv), cytosine (12 miv), uracil (6 mix), or
thymine (9 miv) . Surprisingly, mutant is cystine-nonrequiring, in contrast to cystine-requiring
wild type. That an adenine-resistant virus need not necessarily be cystine-nonrequiring was
shown by selection of a cystine-requiring mutant (still adenine-resistant) by eight passages,
starting with ad mutant, on 30” cultures under medium with 1 mM L-cystine and,3 mM