Breakdown of Я покупаю подарок для моего младшего брата.
брат
brother
я
I
мой
my (мой, моя, моё) / mine
покупать
to buy
Questions & Answers about Я покупаю подарок для моего младшего брата.
Why is it моего младшего брата instead of мой младший брат?
The preposition для (for) always requires the noun and any words describing it to be in the Genitive case. This means the whole phrase my younger brother has to change its endings.
How did the endings for моего and младшего change from their dictionary forms?
The dictionary forms are мой (my) and младший (younger). In the Genitive case, the masculine pronoun мой becomes моего. For adjectives, the standard masculine Genitive ending is -ого, but because the ending in младший comes after the letter ш and is unstressed, the spelling rule changes it to -его, giving us младшего.
Is the letter г pronounced differently in моего and младшего?
Since подарок (gift) is the direct object being bought, why didn't its ending change?
It actually is in the Accusative case, but you cannot see a change! For inanimate masculine nouns (things, rather than people or animals), the Accusative form looks exactly the same as the basic dictionary form. That is why подарок does not get a new ending here.