Why Did Scientists Create Severely Deformed Mouse Embryo with Six Legs?

A recent news article detailed an experiment by developmental biologist Mois��s Mallo and his colleagues who were studying a receptor protein important in embryonic development���Tgfbr1. The article states,

The team inactivated the gene responsible for producing the protein in mouse embryos that were around the halfway point of development, intending to investigate how this change affected the developing spinal cord.

Instead, they found something unexpected: one of the bioengineered embryos had t...