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56
nils nybom
case, the distribution of the individual chromosomes at a triploid
meiosis bas never been studied.
Darlington and Mather (1944) determined the distribution of
the different chromosome types in the pollen grains of triploid
Hyacint hus, and they found that this distribution was nol at random, i.e.
the various types were not distributed independently of each other.
However, these authors were of the opinion that the cause of this
non-random assortment could not be a mechanical hut a physiological
one. Certain chromosome combinations were assumed to be
phvsio-logically unbalanced and for that reason to escape observation at the
pollen mitosis.
The distribution of the Sj chromosomes at meiosis in triploid Allium
Schoe-noprasum. — When studying Levan’s dissertation 011 the cytology of
Allium Schoenoprasum (1935) I found a property of interest connected
with his »Tabelle 24, Das Vorkommen von s^chromosomen in den
ver-schiedenen Klassen von Pollenkörnern», which 1 propose analysing and
discussing here.
The haploid chromosome set of A. Schoenoprasum consists of 8
chromosomes, 7 möre or less medially inserted and 1 satellile
chromosome, termed S, by Levan. One arm of the latter chromosome is
very short and, carrying a satellite, is easily recognized. As seen from
Table 1, Levan had investigated the occurrence of this chromosome in
the pollen grains of an autotriploid obtained by crossing 4x to 2x
A. Schoenoprasum. He also calculated the found and expected
fre-cpiencies of pollen grains with 1S, and 2S, in the various chromosome
number classes.
Ön closer inspection of these values we shall find that in pollen
grains with a chromosome number approaching 8 ( = x) |here is an
excess of pollen grains with lSj and a deficit of 2S1; whereas there is
a deficit of IS, and an excess of 2S, in pollen grains with a
chromosome number approaching 16 ( = 2x). Bv analysis of covariance I tested
whether the distribution of the St chromosomes was independent of
the number of non S, chromosomes present in the pollen grains. v2 for
correlation was 15.65, giving p<0.001. I also calculated the average
number of extra S, chromosomes per pollen grain for the various
classes, and these values are graphicallv shown in Diagram 1 together
with the vallie expected il’ the chance of the pollen grains getting the
extra S, chromosomes was independent of the number of non Sx
chromosomes (p = 0.42).
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