system
Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who] I'm a Time Lord; I want to be a dog

Can I regenerate into a dog? Is that allowed?
gpt
It's pretty unlikely. Regeneration's a bit like throwing down your five cards in Poker and asking for new ones. Your DNA gets shuffled like a deck of cards and then dealt out. Whether you get a full house or a pair of twos out of what you're dealt, there's still the reality that you'll still end up with a set of five cards afterwards just like you had beforehand, even if they don't look the same. You won't suddenly have 2 cards, 2 scrabble tiles, and a Monopoly piece.

Probably the best you could do would be a half-Gallifreyan half-dog hybrid and the dog part may or may not need to be based on a sapient species. 

The hybrid stuff is based on the extended materials such as audio books and so on, there have been some cases where Time Lords have regenerated to include traits from other (sapient) species. Gandarotethetledrax became half Silurian/half Gallifreyan. Another Time Lord, Zero, became half Gallifreyan/half Avian (bird people species) but that also involved an exotic poison. So the couple of cases we have involved sapient species.