worksheet for Problem set 3, January 30, 2006

1.

¤ FOIL method

¤ redundancy in Punnett squares

2.

DO NOT get used to convention. ALWAYS read the problem!!

3.

¤ When labeling a pedigree, choose letters in which the uppercase and lowercase look very different from one another. Aa Bb Gg are good choices. Ss Cc Tt are not.

¤ When dealing with a rare trait like the dread disease “hobbit-toe”, if it is not CLEAR from the pedigree, you may assume that those that marry into an afflicted family are not affected and do not carry the trait.

¤ the multiplication rule

4.

For a family that has 3 children, there are 4 possibilities

♀♀♀

♀♀♂

♀♂♂

♂♂♂

However, ORDER is important! There are ultimately 8 possible outcomes

♀♀♀

♀♀♂ ♀♂♀ ♂♀♀

♀♂♂ ♂♀♂ ♂♂♀

♂♂♂

each condition above has a (1/2)(1/2)(1/2)=1/8=0.125 probability of occurring.

Probabilities always sum to one, e.g. 8 x 0.125=1

Thus, the probability of having one boy is 3 x 0.125= 0.375

Shortcut

p=Pr(event A)

q=Pr(event B)

n=# of trials

s=# of times A happens

t=# of times B happens