(1) atU2-10 and atU2-10b/12 are tanderm duplications, with only 2.5kb between them. It is possible that the U2-10 locus was duplicated again after the chromsome duplication between chr.1 and chr.2 (region b, C.D.1-2b).

(2) Four U6 snRNA genes were located in C.D.1-3b region. As the two genes on Chr.1 (atU6-8p and atU6-9p) have much variation with atU6.1 and atU6.26, it is possible the duplication on chr.3 happened first, then the chromosome duplication between 1 and 3 (region b, C.D.1-3b) happened, so chr.1 also has two copy of U6 snRNA in this region. Both copies on chr.1 may be psudeogenes. Interestingly, several splicing related genes are also in that region, such as LSM1, two SC35 homologs, atOBPa and atOBPb, one hnRNP member and one atCRN homolog..

(3) In C.D.2-3 region, although 4 U2 snRNAs and 2 U5 snRNAs homologs located on chr.3, neither of them have duplication on Chr.2. This indicated that the U2 and U5 homologs in this region may appear after that region duplication.

(4) Most of other snRNAs may come from random duplication.

(5) For details about the chromosome redundancy, please see MATDB.