I'm having doubts about whether the sister chromatids are exactly the same or not. I know that they are the arms that carry the information genes (the alleles), but I don't know if they are exactly the same and / or in what these arms differ, since in a partial exercise they ask me the following:
Explain briefly why the sister chromatids are not exactly the same and the homologous chromosomes are different. To answer, consider the origin of both structures.
Nor do I understand quite well when the statement clarifies "take into account the origin of both structures."
Thank you very much for the help!