G-banding patterns of the chromosomes of amphioxus Branchiostoma belcheri tsingtauense.

Chromosome banding study remains lacking in amphioxus heretofore. This paper reports the G-band patterns of the metaphase chromosomes of amphioxus Branchiostoma belcheri tsingtauense, the first description and numbering of the karyotyped bands in a cephalochordate. G-banding results show that four out of the ten second pair chromosomes examined are heteromorphic, while the remaining ones (6/10) are homomorphic. In contrast, the other 17 pair chromosomes are all homomorphic. These broadly support our previous suggestion that the chromosomes No. 2 are a pair of sex-chromosomes. G-banding method stains positively 65.5% of the chromosome surface, and a total of 149 G-bands (77 positive, 65 negative and 7 variable) has been recorded in the 17 autosomes and the dimorphic chromosomes 2A' and 2A.