abstracts of papers presented at the 1962 meetings - Genetics

ABSTRACTS 943
were the C57BL/6 pure line crosses. In each case the pure line crosses were more prone to fetal
death than were the outcrosses; the C57BL/10 showed more heterosis in crosses than did the
C57BL/G.-Decreasing the quantity of the tetratogen eliminated the differences between the
sublines both with respect to mortality (P > .50) and abnormalities (P > .50). (Supported in
part by USPHS Post-doctoral Research Fellowship BE-10,004.)
BECKER, W. A., Washington State University, Pullman, Wash.: Heritability of a response to
an environmental change.-The relationship of a population in two environments was investi-
gated by weighing young chickens. Progeny of 40 sires and 600 dams were randomly allotted
at hatching to two diets. Males were weighed at four weeks of age while females were weighed
when eight weeks old. Means, heritabilities and variances among individuals within dams for
males on inferior diet were: 236 grams; htq 0.21 f 0.44; h; 0.05 f 0.20 and variance 1,339. Re-
sults on superior diet were: 283 grams; hi 0.29 f 0.63; h; 0.83 f 0.22; variance 875. Genetic
correlation between diets was 0.70 and heritability of the response measured as the difference
between means of progeny on the two diets within a dam family was hi 0.21. Results of females
on inferior diet were: 585 grams; h: 0.41 2 0.68; h: 0.76 f 0.25; variance 4,387. On superior
diet: 680 grams; hi 0.66 f 0.93; hi 0.63 f 0.23; variance 3,486. Genetic correlation between
environments was 0.81 and heritability of response was hs 0.25. Use of logarithmic transforma-
tion did not significantly alter the results.
Results obtained indicated that selecting a strain for a large response to an environmental
change is feasible. Thus, strains of laboratory animals sensitive to specific treatments could be
selected by measuring the response. Also, strains of animals could be selected for resistance to
environmental stresses.
BERG, CLAIRE M., and E. D. GARBER, IJniversity of Chicago, Chicago, Ill.: Color mutants in
Aspergillus fumigatus-Prototrophic-color and auxotrophic-color mutants were obtained by
ultraviolet irradiation of the uninucleate spores of the imperfect species Aspergillus fumigatus.
The former mutants presumably represent mutations involving direct precursors of the parental
dark green color and the latter, mutations resulting in a nutritional deficiency and coincidentally,
an alteration of the parental color. An accumulation of metabolites above normal levels in the
auxotrophic-color mutants may have inhibited pigment biosynthesis by a secondary block. One
group of color mutants was autonomous and the second group was nonautonomous, yielding
green spores at frontiers or in heterocaryons. Two different mechanisms for nonautonomy have
been proposed. Three of the four diploid strains which were studied had green spores and the
fourth, buff spores. Recombinant spores were obtained from diploid colonies grown on complex
medium and, with a higher frequency, from diploid colonies grown on this medium containing
DL-para-fluorophenylalanine. (Supported by funds from the U. S. Public Health Service and
the Abbott Memorial Fund, University of Chicago.)
BIANCHI, A., M. BUIATTI,
Institute of Genetics, University of Milan,
Italy: Recombination frequency in presence of B chromosomes in maize.-Plants heterozygous
for markers of chromosome 9 and differing for presence of B chromosomes us. their absence have
been selfed and/or backcrossed to and by a multiple tester stock homozygous for the appropriate
recessives. The frequencies of crossover in F, possessing no B chromosome were as follows in
the indicated regions: YgSh: 23.09 f 0.38; Sh-Wz: 20.78 f 0.37. When B chromosomes are
present (in numbers of 4-6 mainly, according to personal communication of DR. RANDOLPH
who provided this material) the corresponding values are: YgSh: 22.64 2 0.83; Sh-Wz: 20.04
f 0.75 (The standard error has been calculated making use of ALLARD'S formulas, since F, and
backcross data have been pooled.) The coincidence value is for the former case 0.19, while in the
latter one it turns out to be 0.30.-The data do not indicate that the presence of B chromosomes
and C. VAN DE WALLE,