Answer:
In the given case, the researchers forgot to add DNA ligase after amalgamating the plasmid and gene together. DNA ligase refers to an enzyme, which repairs breaks or abnormalities in the backbone of double-stranded molecules of DNA.
It performs three prime activities, that is, it seals the recombination fragments, seals repairs in the DNA, and its associates or interlinks the Okazaki fragments, which are the small fragments of DNA produced at the time of the replication of the double-stranded DNA. As the mentioned procedure lacks the activities of DNA ligase, due to which only formation of normal pigs took place not the genetically modified pigs.