Synaptonemal
complex karyotype for maize
--Anderson, LK, Stack, SM
We are mapping the distribution of recombination
nodules (RNs) on spreads of maize (KYS) synaptonemal complexes (SCs = pachytene
chromosomes) using electron microscopy. Since RNs occur at sites of crossing
over, an RN map will show the frequency and distribution of crossing over
on each chromosome. This will be useful for integrating molecular, genetic
and cytogenetic maps for maize. As a necessary prerequisite for mapping
RNs, it is necessary to identify each of the ten maize SCs. While several
different characteristics can be used to identify squashed maize pachytene
chromosomes (including relative length, arm ratio, chromomeres, knobs,
nucleolar association), only relative lengths and arm ratios can be used
to identify maize SCs because the other features are usually lost during
the spreading procedure. Nevertheless, we have observed a good correspondence
between the SC karyotype and the pachytene karyotype that is based on squashed
chromosomes (Freeling, M. and Walbot, V., Eds., The Maize Handbook, 1994;
Table 1). The most noticeable difference between the two karyotypes is
for chromosome/SC 6. It is possible that the large nucleolus that is present
in squashes (but dispersed in SC spreads) may obscure part of the short
arm of chromosome 6 and result in a shorter relative length and larger
arm ratio for squashes compared to spread SCs. This work was supported
by grant MCB-9728673 from the National Science Foundation.
Table 1. Karyotype from pachytene chromosome
squashes compared to karyotype from SC spreads.
|
Chromosome or SC rank
|
Pachytene Chromosome squashes
|
SC spreads
|
| |
Arm Ratio
|
Relative Length (%)
|
Arm ratio
|
Relative Length (%)
|
|
1
|
1.23
|
14.5
|
1.25
|
14.9
|
|
2
|
1.14
|
12.4
|
1.08
|
11.9
|
|
3
|
2.0
|
11.3
|
1.97
|
11.0
|
|
4
|
1.63
|
11.1
|
1.54
|
10.7
|
|
5
|
1.07
|
11.1
|
1.10
|
10.9
|
|
6
|
3.1
|
7.7
|
2.57
|
8.9
|
|
7
|
2.6
|
8.9
|
2.73
|
8.6
|
|
8
|
3.0
|
8.9
|
3.05
|
8.6
|
|
9
|
2.0
|
7.7
|
1.93
|
7.7
|
|
10
|
2.6
|
6.3
|
2.45
|
6.7
|
Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.
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