It depends on how you care for your Tamagotchi. If you take good care of your Tamagotchi, you are more likely to get a Mametchi, and if you take bad care for your Tamagotchi, you are more likely to get a Megatchi or Masktchi. But of course you need to remember that there is a bit of randomness when your Tamagotchi evolves. So when you take excellent care of your Tamagotchi you have a better chance of getting Mametchi, but that doesn't necessarily mean you'll get him.
ok.. i took really good care of Patopatotchi and i get a leaftchi.. i'm quite glad.. but in the second generation, if it will have a son with a mimitchi, it's possible for me get another mimitchi?
mimitchi comes only on an even gen.. not so good for me! with my first tama, 7...8.. a lot of time ago, i had always mimitchi.. i'm affectionate with it!