Mitotic and Meiotic Chromosomes ofIchthyophis OrthoplicatusTaylor (Amphibia: Gymnophiona)

摘要

Mitotic and meiotic chromosomes were studied in an Asian caecilian,Ichthyophis orthoplicatus, by a blood culture method and by spermatocyte squashes. For this species, 2N=42, which is the highest chromosome number in the Order Gymnophiona. The karyotype consists of two large metacentrics, one medium-sized submetacentric, three medium-sized metacentrics, two small metacentrics, one small submetacentric, one small subtelocentric, and eleven telocentric microchromosomes. No heteromorphic pair of sex chromosomes is present in either sex. The 21 spermatocyte bivalents have a variable number of chiasmata, positively correlated with chromosome length. The largest bivalent frequently has four or five chiasmata. There are no ring-shaped bivalents. Observations of pachytene bivalents showed a heteropycnotic rod on the end of one arm of bivalent No. 1, and showed that the nucleolus organizer is on chromosome No. 3.