As explained in this eMedTV segment, a mutation in the F8 gene causes hemophilia A, while a mutation in the F9 gene is responsible for hemophilia B. This article covers these genes in more detail and discusses how hemophilia is inherited.
To forward a text message on an iPhone running the iOS 8 operating system, open the conversation thread, select an individual message and then use the Share feature to send the message to one or more of your contacts.
If the activation code to set up text message forwarding is not showing up on your Mac, ensure that an email address is activated for iMessage on your iPhone. Once again, you can activate an email for iMessage on your iPhone by going to Settings -> Messages -> Send & Receive.