NoveMBER 2, 1928}

A GENIC DISTURBANCE OF MEIOSIS IN
ZEA MAYS

Durine and following the summer of 1927, a col-
lection of maize carrying factors for male sterility
(Eyster)! was made for the purpose of genetieal and
cytological investigation. The occurrence of male-
sterile plants in material from thirty or more un-
related cultures suggests the possibility of several
genetic factors causing such sterility.

In segregating material obtained from I. F. Phipps,
it has been found that sterility is due to a recessive
mendelian factor causing irregular meiosis. In a
count of 144 plants the observed ratio was 109 nor-
mal to 35 sterile plants, a deviation from the calcu-
lated ratio of but one plant.2, The cytological be-
havior in these sterile plants has been determined
by studies of the meiotic divisions in the micro-
sporocytes.

Early stages of microsporogenesis in the male-
sterile plants have not been extensively studied. Dur-
ing the stages just previous to and during diakinesis
there is observed a partial or complete failure of
synapsis. Because of this lack of synapsis and the
consequent presence of a large number of univalents,
metaphases are characteristically irregular. Micro-
sporocytes most frequently show twenty univalents.
Progressively fewer cells show one bivalent and
eighteen univalents, two bivalents and sixteen uni-
valents, and so on, cells with ten bivalents rarely be-
ing observed. Some anthers show a high percentage of
sporocytes containing some bivalents while other an-
thers show a high percentage of sporocytes contain-
ing twenty univalents.

Trregularity in the appearance of metaphase J in-
creases with an increase in the number of univalents.
A microsporocyte with ten bivalents in metaphase I
appears normal. When univalents are observed they
do not always lie in one spindle. Usually there is
one major spindle containing the several bivalents,
when present, plus some of the univalents, and one
to several minor spindles containing one or more
univalents (Fig. 1). In consequence of the presence
of several spindles, the sporocyte is divided into a
number of unequal cells after the first meiotic mitosis.
Each cell contains one or more nuclei and each
nucleus contains one or more chromosomes. These
cells undergo a second division to form microspores.
It is obvious that most of these microspores and the
pollen grains formed from them do not contain a
normal haploid set of chromosomes, and they are
probably non-functional under ordinary conditions.

1L, A. Eyster, Journal of Heredity, 12: 138-141.
2 Data partly from I. F. Phipps.

SCIENCE

433

 

This particular type of male sterility is accom-
panied by a certain amount of female sterility.
Several pollinations have given only sparsely-filled
ears. Female sterility has been observed in male
steriles from a few of the other sources also. Mega-
sporogenesis remains to be studied in these cases.

With regard to at least one male-sterile culture, it
may be stated that male sterility is due to a simple
mendelian gene affecting synapsis and consequent
meiotic behavior, the result being the formation of
gametes containing varying chromosomal comple-
ments, only a few of which are viable.

Grorge W. BEADLE

Barpara McCiovrrock
CorNELL UNIVERSITY