Karyotypes ofZamia Chigua(Cycadales)

Abstract

SUMMARY -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.

Intraspecific chromosome variation inZamia(Zamiaceae, Cycadales)

“…Robertsonian changes involved in the karyotypic variation in this genus are uncertain. Centric fusion or centric fission have been suggested to interpret karyotypic evolution in Zamia (NoRSTOG 1980(NoRSTOG , 1981MoRETTI and SABATO 1984; ScHUTZMAN et al 1988;MoRETTI 1990b). In the present paper, new reports on intraspecific chromosome variation in Zamia are presented and their implications discussed in relation to interspecific relationships as well as to karyotypic diversification mechanisms.…”

“…Chromosome numbers ranging from 2n = 16 to 2n = 28 have been reported (NoRSTOG 1980(NoRSTOG , 1981VoVIDES 1983;MoRETTI and SABATO 1984;MoRETTI 1990aMoRETTI , 1990b. In addition, intraspecific chromosome variation, including odd diploid chromosome numbers, has been described in some species (NORSTOG 1980(NORSTOG , 1981MoRETTI and SABATo 1984;MoRETTI 1990b). Robertsonian changes involved in the karyotypic variation in this genus are uncertain.…”

Karyotype polymorphism in the cycad Zamia loddigesii (Zamiaceae) of the Yucatan Peninsula, Mexico

“…The variability in the chromosome numbers reported for Xamia (Norstog, 1980(Norstog, , 1981Vovides, 1983;Moretti & Sabato, 1984;Moretti, 1990;Moretti et al, 1991), with 2n = 16-28, is unsurpassed by any other cycad genus studied so far. <@mi.…”

Chromosome Numbers in Gymnosperms - An Update

“…have 2n=16 while Microcycas shows 2n=26 (Table 1). However, Zamia with 41 species studied shows a dysploid range from 2n=16-28 while Z. chigua (2n=22, 24, 25, 26;Norstog 1980Norstog , 1981 Moretti & Sabato 1984, Moretti 1990, Tagashira & Kondo 1999, 2001, Vovides & Olivares 1996Napalitano et al 2004), Z. prasina (2n=22, 26;Moretti et al 1993) and Z. variegata (2n=21, 22;Moretti et al 1991Moretti et al , 1993 show extensive intraspecific variation (Table 1). All this variability in chromosome numbers without any change in the number of chromosome arms is however, explained by centric fissions as there exists a ratio of one-to-two between median and terminal chromosomes with increase or decrease of somatic number (Olson & Gorelick 2011.…”