Why are the Indian mothers so possessive about their sons?

There are two things at play here: 1) The son is an offspring of the mother. It is natural to get possessive about one's offspring. 2) Although things are changing now, Indian culture has long upheld sons more than daughters. Reasons are traditional — sons are natural heirs of family and property, become breadwinners of the family, and take care of parents in old age; daughters usually move out to their husbands' place. This distinction has been passed on to mothers over generations. However, in today's age, I don't think Indian mothers are any less possessive about their daughters than they are about their sons.