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chromosome distribution in triploid allium 61
1,0
Diagram 1. Showing the connection between the number of extra Si and »ön Si
chromosomes of t lie pollen grains. Broken line indicates expected number of extra Si
chromosomes at random assortment (p = 0.4207).
Of the original number of chromosomes 12X347 = 4164 t here have
been recovered 4005 in the pollen grains, 146 of which are Sj
chromosomes. From this it may be calculated that 16 °/o of the St chromosomes
have been eliminated, this elimination being almost 46 °/o higher than
that of the non Sx chromosomes. This might be due to the fact that
the former ones form chiasmata only in the long arms and therefore
are rather often represented as bivalents and univalents. The destiny
of the lagging univalents at anaphase I is somewhat different in
dif-ferent plants. In certain plants, c.g. No. 646-1, from which the
prepara-tions were taken, the undivided univalents are distributed to Ihe two
poles at the first division. In other plants, ön the contrary, |hey are
usually divided at anaphase I and »random assorted» at the second
division.
The distribution of the chromosome numbers of the pollen grains
showed a verv good agreement with an expected binomial distribution.
I have made a -/^-analysis of the similarity of Levan’s values for found
and expected, and this analysis gåve jr2 = 3.107 and 0.7>p>0.5, thus
a very good agreement.
Interpretation of the case. — The connection found to exist between
the occurrence of S, and non S, chromosomes in the pollen grains may
be formed in two kinds of ways:
1. Physiologicallv. Different chromosome combinations in the
pollen grains may be of different viability, e.g. different råtes of reaching
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