USABO questions

Hi!
I am currently studying for the USA Biology Olympiad, and I am planning to take the Open exam in the coming February (this is my first time).

After looking at some of the past papers, I have realized that I take way too long on Genetics word problems. I also looked at some Semifinal exams and I could not figure out how to solve some of them (like #108,42 to 46 in Semifinals 2012). It would be nice if someone can give me some tips on how to solve Genetics questions quickly, since we only have 120 minutes to finish the whole test (the test has 120 multiple choice questions plus the open ended, so we have less than a minute per question).

Also, I would like to know how exactly the Semifinal exams are graded. In 2013 Semifinals, there are 120 multiple choice questions, and there were some questions worth more than 1 point, so the whole multiple choice section would be worth around 135 points. The open ended is worth a total of around 40 points, so the whole exam is out of 170. However, according to the Biolympiads website, the 2013 semifinal exam is out of 208 points. Because of this, I am confused as to how the Semifinal exams are graded, and it would be great if somebody can clear my doubts.

Thanks!

Anyone?