Preference for a male child is an age old psyche of majority people (male and female both) so is the case with your parents. You can not compel them to give share from their assets. It is solely their wish. If they have inherited assets from your grand father then to get the share is your right and you can demand your share. Still you and your sister convince them for your share arguing that it can give you financial securities for difficult time.
Alternatively, make yourself capable enough to earn your livelihood and feel confident about yourself. Marry a man who can provide you financial and emotional securities. (As I guess, you are full of insecurities).
Joy and enjoyment of your own money is more satisfying then money you get as inheritance.