A pair of non-radioactive, homologous chromosomes replicates once in the presence of radioactive DNA precursors. Assuming that new DNA will incorporate these precursors, which parts of the chromosomes will now contain radioactive atoms?

Both sister chromatids will contain the atoms.

Explanation:

The precursor is a compound that leads to a reaction to form a different substance

The chromosome before it's replicated, is made up of a DNA helix which is in a double stranded form. After it is replicated, there are two helixes and they are joined at their centromeres. The sister chromatids consisting half of the original DNA taking from one parent and the other half of DNA which is newly replicated and this means that both sister chromatids will contain the radioactive atoms/precursors.