DNA supercoiling means under or over winding of the DNA strand and basically is to become more condensed and more organized. Supercoiling is very important as it compacts the genetic code and as if that was not enough supercoiling also regulates and oversees the access the the genetic code.
I have no idea, i speak english how about u
Well, when chromosomes cross over during prophase 1 of meiosis, the homologous pair of chromosomes exchange segments of DNA which happen to be the genes. So the significance of crossing-over during prophase 1 is that it adds genetic variation to sexually reproducing organisms.
