because they contain major portion as of female part
You would call your daughter's son by his name ex: Hi Jack.
His name.
Your daughter is your sister's niece. Your daughter's son is her great nephew.
daughter...daughter in law.
Your grandson.
daughter in law
Your grandson.
daughter in law
Your grandson.
Your son-in-law is your daughter's husband.
you can call him your nephew if you are mom's daughter's sibling or if you will be the mom you can call him your grandson.
Because women reproduce and when the daughter grows into a big cell, then it will reproduce too.