Question

what enables mega nucleus to handle vegetative character and what enables micro nucleus to handle reproductive part if they have same dna?

Answer 1

(While not having read up any more on the paramecium) cells can perform the different functions with the same DNA due to the conditions the cell is in. This is known as regulation of gene expression and different genes are expressed in the presence of certain enzymes and its structure. There are also cascades present, like if one gene is in expression it will cause another gene to be expressed. There is a bit of info on wiki: http://en.wikipedia.org/wiki/Regulation_of_gene_expression

Answer 2

In any organism MOST parts will have the same DNA but perform different functions. This is due to gene expression. The best example is a gene that is regulated by a promotor. The promotor is part of the DNA that does not form a gene (extron I believe). It is activated by a signal - this will most likely be a substances that binds to a receptor protein that then tells the promotor to turn a certain gene on. This is why our whole body has the same DNA but every part of us looks different. Genes are expressed or not due to other parts of the genetic code and the signalling that is received - often by substances called cytokines.