LEQ: What are the basic
rules of probability?
9.7
Probability
The likelihood that a particular event will occur
Rules of Probability
 The larger the sample size,
the closer you get to the
expected outcome
 Past events don’t influence
future outcomes
 Every flip of the coin has a
50/50 chance of being
heads or tails
Rules of Probability
 Rule of Multiplication: the
probability of a compound
event (i.e. 2 coins landing
heads up) is the product of
the separate probabilities
 Independent events
occurring in succession
 AND
 2 coins landing heads up:
 ½X½=¼
 2 heterzygous Gg X Gg
producing gg
 ½X½=¼
 2 dihybrids RrGg X RrGg
producing rrgg
 ¼ X ¼ = 1/16
Rules of Probability
 Rule of Addition: the
probability that an event
can occur in 2 or more
alternative ways is the sum
of the separate probabilities
 Mutually exclusive
 OR
 Cross Pp X Pp what is the
probability of getting
heterozygote?
 Parent 1 P (1/2) and Parent
2 p (1/2) = ¼
Or
 Parent 1 p (1/2) and Parent
2 P (1/2) = ¼
 ¼ + ¼ = 2/4 or 1/2