A scientist inserts a radioactively labeled DNA molecule into a bacterium. The bacterium replicates this DNA molecule and distributes one daughter molecule (double helix) to each of two daughter cells. How much radioactivity will the DNA in each of the two daughter cells contain? Why?

DNA in each of the two daughter cells would have half of the radioactivity as compared to the radioactivity of the DNA of parent bacterium

Explanation:

DNA replication is a semi-conservative process and each of the newly formed double helices contains one parental strand and one newly formed DNA strand. The parent bacterium had both of its DNA strands radio-labeled. Replication of the parent DNA would form two DNA double helices each of which would contain one radio-labeled parental strand and one non-labeled newly formed DNA strand. Therefore, DNA of each daughter cell would exhibit half the radioactivity as that of the parental DNA.