Karyotypes ofZamia Chigua(Cycadales)

Open Access
Publisher Website
Google Scholar
Abstract
Zamia chigua, an arborescent cycad of the Pacific coast of Colombia, South America, has been found to have chromosome numbers of 2n = 22, 24, 25 and 26. Specimens collected from two adjacent populations displayed this range of numbers with karyotypes differing principally in the numbers of telocentric and metacentric chromosomes present in each; 2n = 22, 24, 25, 26 plants were found to have 4, 2, 1 and 0 metacentrics and 12, 16, 18, and 20 telocentric chromosomes, respectively. Because all plants examined in the field demonstrated high fertility, it is inferred that meiosis and fertilization are essentially normal despite differences in chromosome numbers. Zamia chigua, on the basis of morphological and ecological characteristics, is considered to be a primitive member of its genus, and it is thought that chromosome and karyotype evolution in Zamia has occurred by fusion of telocentric chromosomes, producing lower-numbered, symmetrical karyotypes found in apparently more specialized members of the genus.