Nucleolar Organizer Region (NOR) Polymorphism in Some Indian Anuran Amphibian | Chapter 12 | Advanced Research in Biological Science Vol. 8

 The amphibians are the first vertebrate class to colonize the terrestrial environment from the aquatic environment, originating from Crossopterygian fishes in the late Devonian period. They have been the subject of various investigations because of their position in the phylogenetic history, morphological peculiarity, low diploid chromosome number with elongated metaphase chromosome and controversial nature of sex determination. The Indian subcontinent is rich in amphibian fauna. Still, the cytogenetical studies, particularly the karyomorphological study about the distribution of constitutive heterochromatin and nucleolar organizer region (NOR), need to be more detailed. The present book chapter has, therefore, been oriented to describe Amphibia's biology briefly. In addition, cytogenetics of Amphibia with particular reference to constitutive heterochromatin distribution and nucleolar organizer region polymorphism in some Indian anurans such as bufonids, ranids and rhacophorids were written.

 

Conventional staining of mitotic metaphase stages of Bufonid species studied possess symmetrical karyotypes with 2n= 22 and NF = 44. The Ranid and Rhacophorid species the author studied possess symmetrical karyotypes with 2n= 26 and NF = 52. Interestingly, nucleolar organizer region or secondary constriction (SC) region staining by HCl-trypsin digestion and AgNO3 or N-banding technique showed that the number, size and position of NORs are variable in the different species as well in different individuals of the same species. NOR heteromorphism concerning size was also noted between homologous chromosomes of some individuals. The NOR heteromorphism about intraspecific and interspecific variability in size, number and location of chromosomes is very interesting. It would be helpful to solve the phylogenetic relationship among the different species of amphibians.

Author(s) Details:

Samarendra Nath Banerjee,
Department of Zoology, Rammohan College, 102/1 Raja Rammohan Sarani, Kolkata – 700009, West Bengal, India.

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