Pedigree comes through Middle English pedegru from the Anglo-French phrase pé de grue, literally a crane’s foot. The usual explanation connects branching genealogical lines with that shape.
The chart explanation is a historical theory. Etymonline notes that the ancestry sense is not attested in Old French; the French phrase and its later genealogical use are distinct claims.
Sources
- Merriam-Webster: pedigree
Word History gives the phrase, literal meaning and chart-line explanation.
- Etymonline: pedigree
The main noun entry supports the components and qualifies the genealogical explanation and Old French evidence.