In The Merchant of Venice, the circumstances surrounding Portia's upcoming marriage and Jessica's intentions to marry Lorenzo form subplots to the play's main action between Shylock and Antonio and the "pound of flesh" which Shylock insists is owed to him in literal terms.
1. Jessica and Portia are both only daughters of controlling fathers. Even though Portia's father is dead, she cannot escape his influence and her lament is sincere when she says, "so is the will of a living daughter curbed by the will of a dead father" (I.ii.24-25). Portia's filial loyalty (loyalty to family) prevents her from making choices and renders her powerless. Jessica has been similarly bound to her father up until this point and comments that "Our house is hell" (II.iii.2).
2. Jessica and Portia both disguise themselves as men. Due to the laws at the time, there were many restrictions placed on women and therefore Portia must hide her true identity when she poses as the lawyer and saves Antonio from Shylock's bond, which would surely have resulted in Antonio's death. She dresses and poses as a man, successfully reversing the effects of the bond as a result of which Shylock will be forced to convert to Christianity. Jessica also dresses as a man when she flees from Shylock's house and her intention is to avoid notice when Lorenzo comes to fetch her from her father's house.
3. Both women would like to marry for love and do not want to marry simply to meet other people's expectations.
4. Both women take advantage of or outwit Shylock. Jessica runs away with much of his wealth, in particular a precious ring, and Portia, in her disguise, manages to ensure his imprisonment.
5. Both women would have earned the respect of a Shakespearean audience. A Shakespearean audience would certainly have sympathized with both women but would have felt it right and just that Portia should do her father's bidding such as she does and the audience would have been delighted that Jessica manages to usurp her father Shylock because he is a Jew.