The document discusses probability and genetics. It explains that Mendel's laws of segregation and independent assortment reflect the same laws of probability that apply to events like coin tosses or dice rolls. It then provides examples of how to calculate genetic probabilities, such as there being a 50% chance of a dominant trait being passed on, in the same way there is a 50% chance of tossing heads. The rule of multiplication is discussed, stating that the probability of two independent events occurring together is the probabilities multiplied. Examples of applying this to dihybrid crosses and calculating probabilities are also given.

1. Probability &
Genetics
Prepared by: Ma. Jesarene D. Marasigan
AP Biology

2. Genetics & Probability
 Mendel’s laws:
 segregation
 independent assortment
reflect same laws of
probability that apply to
tossing coins or rolling dice
AP Biology

3. Probability & genetics
 Calculating probability of
making a specific gamete P
is just like calculating the Pp 50%
probability in flipping a p
coin
 probability of tossing
heads? 50% P
 probability making a P
PP 100%
gamete…
P
AP Biology

4. Probability & genetics
 Outcome of 1 toss has no
impact on the outcome of the
next toss
 probability of tossing heads
each time? 50%
 probability making a P gamete
each time? 50%
P
Pp
p
AP Biology

5. Calculating probability
Pp x Pp sperm egg offspring
P P PP
1/2 x 1/2 = 1/4
male / sperm
P p P p Pp
1/2 x 1/2 = 1/4
female / eggs
P PP Pp p P
1/2 x 1/2 = 1/4
1/2
p Pp pp p p pp
1/2 x 1/2 = 1/4
AP Biology 2005-2006

6. Rule of multiplication
 Chance that 2 or more independent
events will occur together
 probability that 2 coins tossed at the
same time will land heads up
1/2 x 1/2 = 1/4
 probability of Pp x Pp  pp
1/2 x 1/2 = 1/4
AP Biology

7. Calculating dihybrid probability
 Rule of multiplication also applies to
dihybrid crosses
 heterozygous parents — YyRr
 probability of producing yyrr?
 probability of producing y gamete = 1/2
 probability of producing r gamete = 1/2
 probability of producing yr gamete =
1/2 x 1/2 = 1/4
 probability of producing a yyrr offspring =
1/4 x 1/4 = 1/16
AP Biology

8. Rule of addition
 Chance that an event can occur
2 or more different ways
 sum of the separate probabilities
 probability of Pp x Pp  Pp
sperm egg offspring
P p Pp 1/4
1/2 x 1/2 = 1/4
+ 1/4
p P Pp
1/2 x 1/2 = 1/4 1/2
AP Biology

9. Chi-square test
 Test to see if your data supports
your hypothesis
 Compare “observed” vs. “expected” data
 is variance from expected due to
“random chance”?
 is there another factor influencing data?
 null hypothesis
 degrees of freedom
 statistical significance
AP Biology

10. *END*
AP Biology