I would never use some biometric data to generate my private keys ever.. It is just too simple to reproduce.

Fingerprints: Lift them from your door handle or coffe cup or even your keyboard at work.
Retina scan: One good high resolution photo of your face and you can reproduce it.
DNA: One hair or some skin is enough to gather all you need.

It is one thing to unlock your wallet with biometric data as a second or thrid factor authentication, but generating your private key from this means you can bypass any wallet password or 2fa by just gathering your biometric data.

It could be used as a salt behind your private key though.