abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 973
hours to several weeks, and that this lag is dependent on the particular pair of allelic mutants
combined. Furthermore, the rate of growth of these heterokaryons is also dependent upon the
particular combination of mutants and is not strictly correlated with the lag time. Various ex-
perimental conditions have been studied that have no effect on the individual mutants but which
alter either the time of heterokaryon formation or the subsequent rate of growth or both. For
instance, supplementation of the minimal medium with both 0.1 mg/liter adenine and 200
mg/liter casamino acids brings about a fourfold to fivefold reduction in the lag times found in
most heterokaryon tests with unsupplemented minimal medium. The effect of the D- and L-forms
of various amino acids has also been studied on 26 different combinations of ten complementing
ad-3B mutants. Whereas the effect of D-cysteine was aspecific and resulted in a pronounced re-
duction in the lag time of all combinations, the effect of other amino acids (inhibition or stimu-
lation) on the lag time and growth rate was heterokaryon-specific and not limited to the L-forms
alone. Almost all possible relationships between the D- and L-forms on the lag time and growth
rate have been found. The significance of these findings in the term of the mechanism of allelic
complementation will be discussed. It appears, however, that allelic complementation is a complex
phenomenon with at least two separate and independent phases. (1 Permanent address: Istituto
Superiore di Sanita, Rome, Italy.)
NAYLOR, ALFRED F., McGill University, Montreal, P.Q., Canada: A new rigorously-proven
theorem on mating systems.-All of several actually known or hypothetical mating systems of
the negative assortative type have either of two features: (1) a characteristic equilibrium allelic
frequency which is independent of initial frequency; or, (2) special conditions which make the
actual mechanism of the “system” dependent on the gene frequency which is to be maintained
while heterozygosity increases in the population. This remark is extended to a theorem, which,
while not momentous, is biologically novel in that it is an absolutely provable generality. An intuitive
interpretation will accompany the elementary proof.
NORBY, D. E., H. C. THULINE, and J. H. PRIEST, Rainier School, Buckley, Washington: X
chromosome differentiation in relation to coat patterns in cats.-Application of LYON’S hypothesis
of differential sex chromosome inactivation to the expression of the genes producing black and
yellow mosaic coat color in female cats depends upon establishment of their sex linked pattern of
inheritance. The demonstration of an extra chromosome in males with these colors overcomes
many of the past obstacles to the acceptance of such a pattern.-The expression of these alleles
appears to be influenced by the autosomal gene which controls the presence of white spotting.
In the presence of the spotting gene the colored patches are large; if its recessive allele (solid
color) is homozygous the patches are very small. Assuming that inactivation of one of the two
X chromosomes is responsible for the mosaicism, the size of the patch will be related either to the
time of inactivation during embryogenesis or to the specification ,of the chromosome inactivated
in the cells of a given patch. Thus, the postulated X chromosome inactivation would be under
autosomal control in one or the other of these two aspects.
NUFFER, M. G., University of Missouri, Columbia, MO.: Consideration of the suppressor ele-
ment hypothesis for mutable loci.-The generally accepted hypothesis for induction of muta-
bility at a particular locus by the two unit mutator systems found in corn is that an undefined
element moves to a gene site (A, for example) under the influence of a second element (Dt) and
while there suppresses the action of the gene so that it expresses a recessive phenotype (a). This
phenotype continues until the element moves away at which time normal gene function is re-
stored producing sectors of A like tissue, hence the designation p. In the absence of Dt, am is
completely stable but when after many generations the two factors are again placed in the
same cells reversions to A occur. If am is A with a separable element suppressing it one would
expect that the element may be dislodged or destroyed (in the absence of Dt) by chemical muta-
gens, UV or perhaps even with X rays. Such a dislodging without loss of A should produce a