Chances of AIDS/HIV between straights and gays?

Men and women have the same chance of getting HIV, all other factors being equal. Gay men, currently, have a higher chance simply because there are more gay men that have HIV than straight men. Lesbians can get HIV also, from fluids transfered during sex, just like everyone else. Oral sex can transfer saliva and blood both, and during oral sex you get exposed to either vaginal fluid, blood, or semen. The reason why you don't have a 100% chance is because there is the chance that the fluid you pass won't have the virus in it, or the odd chance the fluid might not get to a membrane it can pass through. Infection is spread by chain, in which you must have 3 elements: a source, a host, and a method of transmission. NOTHING has a 100% chance of spreading. I don't know about the 1/500. All I know for sure is, abstinence decreases your chances greatly since it isn't as easy to get from kissing/fondling, and using a condom/dental dam also makes a very large difference in your odds. And, there are other, more common things to catch out there that these help protect you from, like Hepatitis and Herpes.