Experiment Station Record, Volume 92, January-June, 1945 Page: 33
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19451 GENETICS 33
wheats, while the other 6 (XV to XX) involve chromosomes not represented in the
emmers. While all are reduced in vigor to various degrees all mature, and none
is completely sterile. Locations of several genetic factors, revealed by the nullisomics,
include a factor for red seeds on chromosome XVI, the hooded factor
(Hd) for recurved awns on VIII, the awn suppressor B2 on X, and factors for
promotion of awn growth on II and XX. The speltoid chromosome, with the
factors for pubescent nodes, squareheadedness, and suppression of awns, is IX. The
recessive bi on chromosome IX, whose dominant allel inhibits awns, also inhibits
awns to a small extent. Differences in recovery of nullisomics in frequencies of
less than 1 to more than 10 percent in progenies of monosomics depend mainly
on elimination of different proportions of the deficient pollen. Apparently about
75 percent of functioning female gametes are deficient regardless of the chromosome
concerned. Tetrasomics occurred among offspring of trisomics in frequencies of
about 1 to 10 percent. One tetrasome involves chromosome II and compensates
almost completely for nullisome XX. Another tetrasome compensates partially for
nulli-XVI, and a certain trisome largely compensates for nulli-I. Telocentrics and
isochromosomes occurred fairly frequently among offspring of monosomic plants,
following misdivision of the univalent chromosome.
Cytological basis for sterility in induced autotetraploid lettuce (Lactuca
sativa L.), J. EINSET. (New York State Expt. Sta.). (Amer. Jourr. Bot., 31
(1944), No. 6, pp. 336-342, illus. 9).-Induced autotetraploids exhibit varying degrees
of fertility ranging from values as high as those in many natural autotetraploids
to complete sterility. Studies of induced autotetraploids of lettuce
indicated that partial sterility of these plants is conditioned by two main factors.
In about 20 percent of the ovules the meiotic process breaks down and the embryo
sac does not develop. In the remaining 80 percent of the ovules, the embryo sacs
appear normal but in only a small percentage (0L-25 percent) do the pollen tubes
reach the sacs and effect fertilization. The similarity of the observed sterility to
partial self-incompatability is indicated.
A new male-sterile mutant in the tomato, C. M. RICK. (Univ. Calif.).
(Science, 99 (1944), No. 2583, p. 543).-The labor required in emasculating and
pollinating the flowers of the tomato has prevented the economic use of the procedure
to obtain the increase in yields due to hybrid vigor. If it were possible to
use a male-sterile variety as ovule parent, the need of emasculation would be
eliminated. The author describes such a plant found at Davis, Calif., and shows
how the character of male sterility behaved in F1, F2, and backcross generations.
Male-sterile plants may be found occasionally in the field and are noticeable because
of their unusual vegetative development.
Lethal and sublethal characters in farm animals: A check-list and proposed
numbering system, I. M. LERNER. (Univ. Calif.). (Jour. Hered., 35 (1944),
No. 7, pp. 219-224).-Brief descriptions are presented of the lethal characters in
cattle, horses, swine, sheep, chickens, turkeys, and ducks, bringing the descriptions
previously presented by Eaton (E. S. R., 78, p. 769) up to date. Proposals for
a number system for lethals are presented.
A genetic analysis of recent Thoroughbreds, Standardbreds, and American
Saddle horses, D. G. STEELE (Kentucky Sta. Bul. 462 (1944), pp. 27, illus. 8).Study
of breeding practices followed in the development of stake winners or "poors,"
arbitrarily selected in these breeds of light horses by methods of Wright and
McPhee (E. S. R., 54, p. 324), showed that current breeding practices were similar
to those reported for other farm animals. The prejudice against close breeding,
particularly in Thoroughbreds, is probably greater than with other farm animals.
In all of the breeds, mating of the best to the best is practiced, and meritorious
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U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5064/m1/46/: accessed June 28, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.