The more you have of one gender the better the chances of having more of the same... It increases exponentially...I think...
This is not correct.
For background, I was a math major with an A grade in advanced statistics, so I do know a little about the subject.
Take something with a 1/2 probability of occuring, say a coin toss coming up heads. The probability of tossing a coin three times and having heads come up each time is the probability of getting heads 1 time multiplied by three. i.e., 1/2 x 1/2 x 1/2, or 1/8. To illustrate, let's plot all the possible combinations.
h h h
h h t
h t h
h t t
t h h
t h t
t t h
t t t
That's 8 possible combinations, of which only 1 is all heads. So, our math checks.
This is not the same as saying a man rolls a coin three times, and the first two times are heads. What is the probability of the third roll being heads?
The facts in this scenario have already eliminated all possibilities that do not have heads in the first two rolls. So, taking our rolls from before with bold deleting impossible answers:
h h h
h h t
h t h
h t t
t h h
t h t
t t h
t t t
We see that there are only two possible outcomes left in this scenario. So, the chances of the third roll being heads are 1/2. Make sense?