Cytogenetic analysis of chromosome number and ploidy of Carassius auratus variety pengze

Carassius auratus variety pengze is a commonly farmed fish in China. Defining the chromosome number and ploidy of Carassius auratus variety pengze is important to understanding the genetic material, regulation of hereditary variation, developmental mechanism and evolution relationship of this species.Metaphases of Carassius auratus variety pengze were prepared directly from kidney cells in vivo. Chromosome number in all counted complete metaphases of Carassius auratus variety pengze is over 150, and the highest chromosome number in the examined matephases was 169. 86.4% of metaphases had 151 to 161 chromosomes, but there were no multitudinous distributions from 151 to 161. 4.4% of metaphases had more than 161 chromosomes. Metaphases in which the chromosome number was over 150 had some small chromosomes.Analysis of karyotypes showed that the 150 basic chromosomes can be divided into four sections according to the position of the centromere. There are 33 metacentric chromosomes, 51 submetacentric chromosomes, 33 subtelocentric chromosomes and 33 telocentric chromosomes. In each section, homologous chromosomes were grouped according to their relative length and arm ratio. Each homologous chromosome group contained three complete matched homologous chromosomes. Metacentric chromosomes could be grouped into 11 groups, submetacentric chromosomes into 17 groups, subtelocentric chromosomes into 11 groups and telocentric chromosomes into 11 groups. The number of homologous chromosome groups in each section is as much as the number of homologous chromosome pairs in diploid species of the Carassius auratus. In metaphases in which the chromosome number is over 150, there was an unstable number of small chromosomes that can not be classified into the four sections. Therefore, these small chromosomes can be considered supernumerary chromosomes. In the subtelocentric chromosome section, all of the three chromosomes of the third homologous chromosome group have satellites on their short arms. These satellite chromosomes can be identified only at middle metephase. At premetaphase and prophase, it is difficult to distinguish the chromosomes with satellites due to loose structure of the chromosomes. In the later metaphase satellite chromosomes can not be observed easily because of the tightness of the chromosome. Obviously, these three satellite homologous chromosomes can be regarded as cytogenetic characteristics of triploid chromosomes. The DNA relative content of muscle cells of Carassius auratus variety pengze and Carassius auratus variety red were measured using a flow cytometer. The DNA relative content of muscle cells of Carassius auratus variety pengze is 82.85±1.93(13 specimens). In the classical diploid control group of Carassius auratus variety red, the DNA relative content of muscle cells is 53.32±1.62(7 specimens). The ratio of DNA relative content of Carassius auratus variety pengze and that of diploid Carassius auratus variety red is 1.55∶1. This is consistent with the analytic result of chromosome. These results suggest that Carassius auratus pengze is a triploid Carassius auratus with a chromosome number of 3n=150+. Statistical analysis of the chromosome number of kidney cells shows that the chromosome set of Carassius auratus variety pengze consists of 150 basic chromosomes and 0 to several small supernumerary chromosomes. The karyo formula is 3n=33 m+51 sm+33 st+33 t [Acta Zoologica Sinica 49(1):104-109,2003].