difference between sister and non-sister chromatids
Sister chromatids are identical to each other. During S phase of the cell cycle the DNA is replicated and an identical copy of the chromatid is made. These two chromatids are then called sister chromatids. Nonsister chromatids are not identical to each other as they represent different but homologous chromosomes. The non-sister chromatid will carry the same type of genetic information, but not exactly the same information.Homologous chromosomes carry the same type of genetic information, for example information for seed shape in peas, but they may not carry exactly the same information, for example one has information for round seeds and one for wrinkled seeds. Homologous chromosome will also have the same size and position of the centromere. Nonhomologous chromosomes have different types of genetic information, and they are probably not the same size and with the centromere in the same position.
Swetha has posted a very appropriate answer to your question. Hope you find it useful.
@Swetha, Great answer, we really appreciate your contributions to this forum. Keep posting answers because like Saloni, hundreds of other students will be benefitted by these answers. You deserve a thumbs up from the experts for your efforts. Keep up the good work going!