Muggles' Guide to Harry Potter/Magic/Metamorphmagus

Overview
A Metamorphmagus is a witch or wizard who has the ability to change their appearance at will, without the need for a wand, spell, or potion.

Extended Description
Metamorphmagy is a very rare ability, and one that a witch or wizard must be born with. There is no way for one to train in order to become a Metamorphmagus.

Nymphadora Tonks, who is first seen in Harry Potter and the Order of the Phoenix, is a Metamorphmagus. Tonks tells Harry that her natural metamorphic abilities helped her greatly during the Concealment and Disguise portion of her Auror training, to the point that she didn't even have to study. Throughout the fifth book, Tonks changes her hair color and style quite often, with her preferred style being short, spiky, and bright pink in color. She has also been shown to be capable of changing a number of her facial features at will.

Analysis
Throughout much of Harry Potter and the Half-Blood Prince, Tonks was shown to not be using her Metamorphmagus ability in any capacity. Harry believed that this was because she was mourning someone and her sorrow either prevented her from changing her appearance, or simply left her uninspired to do so.

Questions

 * 1) Sirius Black is related to Tonks – she is his distant niece. Could he also have some Metamorphmagus ability? Could that have helped him when he went through the spells necessary for him to become an Animagus?