Fathers name on I-129F and birth certificate

[Preeta511]

Hello All,

As per the I-129F, should the beneficiary’s biological father or step father name be entered ?
I am the beneficiary and my mother had a divorce and was re-married, therefore my father is my step father but there is no adoption document.
According to my birth certificate I have my biological father’s name on it. But my passport has my step father’s name on it.
I need some advice as to what father name should be entered in both I-129F and DS-160 forms or will I have to have my step father adopt me legally ?

Any advise would be appreciated !

Thanks