The recombinant plasmid method is used for identifying sequences that can serve as origins of replication. The DNA of interest is fragmented into pieces that are ligated into plasmids, and the plasmids are transformed into host cells. To form colonies, the plasmids must contain a sequence that can serve as an origin of replication. The recombinant plasmid method has worked for identifying E . coli and yeast origins, but not origins for higher eukaryotes like humans. What is the most likely explanation for this observation? The ends of human origins of replication are unable to be ligated into plasmids. Human chromosomes do not contain origins of replication. Human origins of replication are probably determined by a chromatin structure unable to form in this assay. Legally speaking, human cells cannot be used in a laboratory. .