POPULATION CYTOGENETIC STUDIES CONFIRM X-Y MECHANISM IN ISOETES PANTII ( ISOETACEAE : PTERIDOPHYTA)

Chromosomal surveys of Isoetes species in the ponds in and around Narsinghgarh area in Central India have revealed the evolution of X-Y chromosome mechanism. While Isoetes pantii Goswami and Arya is still characterized by variable chromosme number on account of its being a natural hybrid, the plants with 2n=36,39 and 2n=48 always possess heterosporous microsporangia containing highly abnormal megaspores of enormous evolutionary significance. Origin of sex chromosomal mechanism appears to coincide with the evolution of heterospory within the microsporangia, a feature not yet known in any other living plant. On the basis of earlier and present experimental approaches by DNA finger printing, the emphasis is laid on resemblances of some genomic DNA sequences of I pantii to a few human Y chromosomal sequences. Brief comments on recent discoveries of human Y chromosome MSY region DNA sequences by different authors in a bryophyte, Marchantia polymopha and in several other plants, have also been discussed particularly with the intention that our hypothesis advanced during 1990s that the plants have some sequences from human genome or vice versa, appears to be valid. All these observations also support our earlier hypothesis advanced on the basis of genomic studies as well as computer search (DNA blasting) of a part of Isoetes genomic DNA with the human genomic data, that the DNA sequences, must have ceaselessly replicated and randomly distributed among evolving cells before the bisecting of evolutionary lineage to plant and animal cells during Pre Cambrian.