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!

  • 1
    $\begingroup$ Well, what is the origin of the sister chromatids? In other words, by what process does a cell go from one chromosome consisting of one DNA molecule to one chromosome consisting of two DNA molecules (two chromatids)? $\endgroup$ – canadianer May 10 '18 at 18:53
  • $\begingroup$ Then the sister chromatids would be formed from the DNA replication? $\endgroup$ – Osrion May 10 '18 at 19:51
  • 1
    $\begingroup$ Yes exactly. Now, is DNA replication perfect or are errors introduced? $\endgroup$ – canadianer May 10 '18 at 19:53
  • $\begingroup$ I suppose it is perfect or is it possible that there are errors? $\endgroup$ – Osrion May 10 '18 at 20:58

A new chromatid is synthesized by copying the other chromatid. As such two sister chromatids are (quasi) perfectly identical.

Why did I say quasi? Because there are sometimes "errors" when replicating DNA. These "errors" are called mutations. As far as I know, most mutations occur during meiosis though and only very few occur during mitosis. So, to a pretty good approximation, yes sister chromatids are identical.

| improve this answer | |
  • $\begingroup$ Ohh ok, with this I understood what canadianer means. Thank you very much for the explanation! $\endgroup$ – Osrion May 11 '18 at 15:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.