q/"2N-1 CHROMOSOMAL CHIMERA

INMAIZE

BARBARA hlc!&x~ocK

u         Hofat1j' Dipartlllcrzl,
W IIILE investigating the chromo-
    some numbers in an FZ genera-
     tion  of a cross of triploid
maize (Zca 1~1~s) by diploid maize,
an individual appeared whose micro-
sporocytes showed a 2n - 1 chromo-
some complement. The diploid chro-
mosome number in maize is 20. Sporo-
cvtes of such plants normally show 10
Gvalents at metaphase of the first
meiotic division.

`I`he presence of sporocytes showing
only nine bivalents and one univalent
(see Figure 20) in the first aceto-car-
mine smears led to a #further investi-
gation of  the chromosome comple-
ment in other parts of the tassel. The
plant was ver}  small and the tas-
sel poorly developed, but approximately
150 clear figures were obtained from
several different regions of the tassel.
In all cases the sporocytes showed
clearly 19 chromosomes, usually in the
form of nine bivalents and one uni-
val:nt.

In anaphase the components of the
nine bivalents disjoined and passed
regularly to the two poles.  The uni-
valent usually lagged at the equator
after the bivalents had disjoined, or
lagged and split, the halves very fre-
quently being eliminated from lthe re-
organizing telophase nuclei.

S:veral root tips were examined and
all clear figures showed 20 chromo-
somes.

Such evidence points to the fact that
early in the ontogeny of the upper part
of this plant a chromosome must have
been lost. Such occurrences are prob-
ably not rare, but their detection is,
since there are so few cas:s men-
tioned in the literature*.  Unfortu-
nately, for some undetermined reason,
the plant gradually died before matur-
ing pollen.

Cornell Ijllizvrsity

; =' . .._

LACKING A CHROMOSOME
       Figure 20

Photomicrograph from an eight months'
old  permanently  mcunted  aceto - carmine
smear showing a late metaphase figure with
nine bivalents and one univalent. Made with
the aid of a Leitz "Makam" camera, a
periplanatic ocular, 1.8 mm. N. A. 1.25
Spencer achromatic objective, and a Wrattell
green filter ?;o. 56. Magnification approxi-
mately 650x.

  *BLAKESLEE. A. F., and UELLING, J.  Chromoscmal chimeras in the Jimson weed
SCiCIfCE, 55 :19-20.
                          218