Abstract
The diploid chromosome number of 13 species belonging to the family Araneidae (Araneae) ranges between 16 and 25. The ♂ sex-determining mechanism seems to be X1X2X3X4O in one species; X1X2X3O in three species and X1X2O in the remaining 9 species. The X1X2X3X4O, ♂ sex-determining mechanism is reported for the first time in spiders. All the chromosomes are with terminal centromeres. C-band preparations in 5 species suggest procentric localization of constitutive heterochromatin in all the chromosomes, though distally located C-band positive blocks are also visible in a few chromosomes. It is suggested that chromosomal evolution in this family has taken place by gradual reduction in diploid number through tandem/centric fusion followed by pericentric inversion in autosomes and nondisjunction/duplication of one X, with subsequent loss of homology in sex chromosomes.
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