Chromosomal Variation

Among different species, there is some varioation in chromomsome numbers that are tolerated by the species.  For example, plants are quiet tolerant and can survive with varying chromosome number.  In nature, three mechanisms which chromosome numbers can chamge is through meiotic nondisjunciton, mitotic abnormalities, and interspecies crossing.  Meoitic nondisjuction is when the chromosomes do not seperate properly during gamete production.  This can happen in both meiosis 1 and meiosis 2.  In meosis 1, gametes are monosomic and trisomic.  In meosis 2, half the gametes formed will be normal while the other half are abnormal.  In a very rare case, there is complete nondisjuction when all the chromosomes go to a single cell.  For example, a dipoloid species would form a tetraploid species.  The condition is called autopolyploidy.  In interspecies crosses, the recult is allopoidy.  The first generation with the cross will likely survive but when the chromosomes line up  in meosis there might be some issues.  It is possible but not likely.