"Yağız´ın Ömer´in oğlu olduğuna inanmıyorum!"

Can someone please explain to me why do we add " ´ın " after "Yağız" and why " ´in " after Ömer? And what does that mean.. and give examples, please.

Çok teşekkürler.

´ın and ´in are for possession. But I´m not able to explain the whole sentence. The ´i´ changes based on the last vowel to whatever you are adding the suffix to.

But I found this convenient chart from here: http://www.turkishclass.com/turkish_lesson_221

This means if the last vowel is an a, the suffix will contain an ı and so on. This is called vowel harmony. It is supposed to make things easier to say.

[Yağız´ın [Ömer´in oğlu] olduğuna] inanmıyorum!

The genitive case has many functions. The basic function  -  possession  -  can be seen in Ömer’in oğlu ‘Ömer’s son’.

Another function is grammatical. When you make a sentence

Yağız Ömer’in oğlu

a constituent of another sentence like

İnanmıyorum: Yağız Ömer’in oğlu.

(LIKE Sana/Allah’a/Aşka inanmıyorum.)

you must mark somehow that this sentence has been subordinated/embedded and it is not an independent sentence any more. This is where Turkish language uses genitive marking for the subject (and participle marking for the predicate). So,

>>>> Yağız’ın (GEN) Ömer’in oğlu olduğuna (PART) inanmıyorum. ‘I do not believe Yağız is Ömer’s son.’