Title: The karyotype of Rana pipiens and investigation of its stability during embryonic differentiation
Abstract: The Rana pipiens karyotype has been determined from embryonic cells in order to have a basis for detecting abnormal chromosomes in future studies and to investigate whether the karyotype undergoes any changes during the cellular differentiation that accompanies normal embryogenesis. Metaphases from the undifferentiated cells of the early gastrula and from the differentiated cells of the postneurula tail were analyzed from permanent squash preparations. The material was first exposed to prefixation treatment, then fixed, stained, and squashed. The 26 chromosomes have been classified into 6 pairs with median centromeres (group I nos. 1–4; II nos. 5–6) and 7 pairs with submedian centromeres (group III nos. 7, 8; IV nos. 9, 10; V, nos. 11–13). All the chromosomes can be identified individually with the exception of group II nos. 5, 6 and Group V nos. 11, 12 which are usually difficult to distinguish from each other. No heteromorphic pair of (sex) chromosomes is present. The karyotype of the undifferentiated early gastrula cells and the differentiated cells of the diploid and haploid androgenetic postneurula tails is basically identical. Two variations are present. Early gastrula chromosomes are longer than chromosomes of tail cells, and the secondary constriction present in the no. 10 chromosome is longer in gastrula chromosomes. A statistical analysis of relative lengths of chromosomes 1 and 4 showed that each of the chromosomes of the three cells types contributes the same percentage to the genome. The difference in absolute length at different stages is attributed to different degrees of chromosome despiralization. Centromere positions in Chromosomes 1 and 4 also do not differ significantly among the three cell types. However, the secondary constriction of no. 10 is significantly longer in early gastrula chromosomes. Chromosome length is discussed briefly in relation to ploidy and to nuclear and cell size. Chromosome studies on other Anura are related to those on Rana pipiens. The controversy concerning the existence of a pair of heteromorphic (sex chromosomes in Anura is reviewed.
Publication Year: 1962
Publication Date: 1962-08-01
Language: en
Type: article
Indexed In: ['crossref']
Access and Citation
Cited By Count: 83
AI Researcher Chatbot
Get quick answers to your questions about the article from our AI researcher chatbot