After crossing over, two chromatids are most likely to have a new sequence of dna bases if they: a. became more like each other. b. became more like chromosomes. c. are not sister chromatids. d. have not yet separated.

The answer is C. Crossing over mostly occurs during meiosis I when sister chromosomes are lined up in the metaphase plate awaiting anaphase I where the sister chromosomes are pulled to separate daughter cells by spindle. It is during this period that the chromatids of the sister chromosomes come together at a point (chiasma)  and share genetic material in a process called crossing over.  

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