You suspect a cell that is capable of forming gametes might be carrying a gene that makes it defective in homologous recombination. Design an experiment to assess its homologous recombination capability

Question

What will be an ideal response?

Answer 1

Answer: This requires being able to label an entire chromosome or at least multiple locations along its length. Labels used in classic experiments include 15N/14N or 3H-thymidine. More modern approaches might involve using molecular probes that bind to several different genes spread across a chromosome. As J. Herbert Taylor did, one could then label one DNA strand of each chromosome double helix during the DNA replication phase of the mitosis prior to meiosis in the absence of the label. During the following S phase, DNA replication in the absence of 3H-thymidine generates chromosomes containing one labeled chromatid and one unlabeled chromatid. If homologous recombination is inhibited in the cell, all individual chromatids would remain either completely labeled or unlabeled during the subsequent meiosis. Finding individual chromatids with a mixture of radioactive and nonradioactive segments would indicate homologous recombination had occurred.