The two actors don't look much alike, but have taken great pains to cultivate similar poses, expressions, behaviors and habits. Well spotted.

Davina wrote:

That is the genius of thorough formation of character. I love it when you hear similar speech patterns too.

Just found one:

Here is another attutude the two brothers have in common - according to the view of John and Irene:

One more thing Mycroft and Sherlock have in common: Both do pour the tea.
In fact, they are the only ones to be seen doing so in the whole series (apart from Soo Lin's demonstration for the tourists and her working on the ancient tea pots).

Well observed, QE. 

Brillant!

I love those two and the complicated and very interesting relationship they have.

One of my favourite Holmes bros moment is in the Great Game, when Mycroft pays a visit to his brother to ask him to investigate on the death of Andrew West.

Look at them sitting in front of each other in a similar position, like they were each other's reflection in the mirror...



Both playing with their fetish objects and focusing on them...

Sherlock's violin...



Mycroft's umbrella...




And I just LOVE that moment Sherlock asks John "How's Sarah, John? How was the lie-low" and Mycroft corrects him and says "Sofa, Sherlock. It was the sofa." (John's face as his reactions to these deductions is just priceless) : this is a subtile way to show Mycroft's power of deduction even surpasses Sherlock's, as stated in the canon.