Data from: High-resolution crossover maps for each bivalent of Zea mays using recombination nodules

Recombination nodules (RNs) mark sites of crossing over along pachytene
synaptonemal complexes (SCs). Thus, RNs provide the highest resolution
cytological marker currently available for defining the frequency and
distribution of crossovers along the length of chromosomes because they
are observed by electron microscopy. Using the maize inbred line KYS, we
have prepared an SC karyotype in which each SC was identified by relative
length and arm ratio and related to the proper linkage group using
inversion heterozygotes. We mapped 4272 RNs on 2080 identified SCs to
produce high-resolution maps of RN frequency and distribution on each
bivalent. Average RN frequency per bivalent is closely correlated with SC
length. The total length of the RN map is about two-fold shorter than most
linkage maps, but there is good correspondence between the relative
lengths of the different maps when individual bivalents are considered.
Each bivalent has a unique distribution of crossing over, but all
bivalents share a high frequency of distal RNs and a severe reduction of
RNs at and near kinetochores. The frequency of RNs at knobs is either
similar to or higher than the average frequency of RNs along the SCs.
These RN maps represent an independent measure of crossing over along
maize bivalents.