Cytogenetics of Trisomics and Tetrasomics in Some Species of Iberis L. (Cruciferae)

Abstract

Four species of Iberis, I. amara, I. pectinata, I. umbellata and I. saxatilis collected from Great Britain, all over Europe and some areas in the Mediterranean (not in Europe) were studied.
They were shown to have normal flower buds with regular ratio between the length of the large sepal which partially encloses the rest of the bud. They had abnormal flower buds as well in which the above ratio was altered considerably. The abnormal flower buds were also sterile and had some malformations affecting the reproductive parts.
Cytological studies established chromosome counts in both normal and abnormal buds:
I. amara 2n=14 (normal); 2n=15 (abnormal)
I. pectinata 2n=14 (normal); 2n=15 (abnormal)
I. umbellata 2n=18 (normal); 2n =19, 20, 22 (abnormal)
I. saxatilis 2n=22 (normal); 2n=23, 24 (abnormal)
Strong evidence was presented indicating that the extra chromosomes in the abnormal buds were trisomics and tetrasomics (with occasional double tetrasomics). Correlated with translocations and multiple bivalent secondary associations (also demonstrated in the species studied) and with external morphological differences, it appears that the trisomics and tetrasomics could serve to explain the aneuploid increase in the Genus from n=7 to 9 and to 11.
Interspecific crosses among all the species produced only one type of hybrid, I. pectinata female×I. amara male. Results from the interspecific crosses as well as sterility of abnormal buds indicated that there is a strong genetic barrier between species and gametes with different chromosome numbers.