DNA synthesis can be specifically measured by estimating the incorporation of radio-­labelled:

Explanation

DNA synthesis can be specifically measured by estimating the incorporation of radio-labeled thymidine.Thymidine is one of the four nucleotides that make up DNA. When cells are incubated with radio-labeled thymidine, they use the radio-labeled thymidine to synthesize DNA and incorporate it into their DNA backbone. So, thymidine is an excellent measure of DNA synthesis in cells that have undergone the S-Phase of cell replication. The other options that you listed are not as specific measures of DNA synthesis: Uracil is a nucleotide that is found in RNA, not DNA. Deoxyribose is a sugar that is found in DNA, but it is not specific to DNA synthesis. Adenine is a nucleotide that is found in DNA, but it is not as specific to DNA synthesis as thymidine.