1. Probability & Genetics
Drawing from the Deck of Genes
Probability & Genetics

2. # of all possible outcomes
PROBABILITY
Likelihood that a specific event will occur
Can be determined by a formula:
Probability = # of one kind of possible outcome total
# of all possible outcomes

3. Predicting a chance event
Use probability to figure out your chances of pulling cards out of a deck.
Predict possibility of genetic traits appearing in offspring

4. 1,3,5 3/6 = 1/2 What is the probability of a coin landing heads up?
What is the probability of a coin landing tails up?
3. You have a deck of cards ( 52 cards). What is the
probability of picking two red queens?
2/52 X 2/52 =
4. A die has six sides. What is the probability of rolling an odd number?
1,3,5
3/6 = 1/2

5. FIRST LAW OF PROBABILITY
Probability has NO MEMORY
6. If you toss a coin 100 times, what is the probability it will land on heads?
1/2
7. You have tossed a coin 10 times and each time it has landed on heads, what is the probability the next toss will land tails up?
1/2

6. FIRST LAW OF PROBABILITY
“The outcome (result) of a chance event is never influenced by previous results.”
EXAMPLE:
Chances of have a boy?
After having 3 or 4 girls, what are the chances for a boy ?
1/2
still 1/2

7. Second Law of Probability: PRODUCT RULE
“Probability of 2 chance events occurring together is the MULTIPLICATION PRODUCT of the individual probabilities.”
8. What is the probability of tossing two heads in a row?
½ x ½ =
9. What is the probability of tossing four heads in a row?
½ x ½ x½ x ½ =

8. PUNNETT SQUARES Can be used to PREDICT Important in Genetics because:
Used to predict FREQUENCY Of gametes and offspring
Valid only when LARGE NUMBERS are used
gametes

9. Genetics & Probability
Mendel’s Laws:
Segregation
Independent assortment
Reflect same laws of probability that apply to tossing coins or rolling dice

10. Second Law of Probability
The rule of multiplication
To find the probability of 2 chance events occurring together
Multiply product of their separate probabilities
½ B X ½ b = ¼ Bb
F1 Genotypes
B b female
B b male
Formation of eggs
Formation of sperm
1/2 B B
1/2
1/2 B B b b
1/4
1/2
(1/2  1/2) b B B b
1/4
1/4 b b
F2 Genotypes
1/4
Figure 9.13

11. 2nd Law of Probability
Ex: If your chances of pulling an ace from a deck of cards is 4/52 (1/13) and
Your chances of pulling a heart is 13/52 (1/4) , then your chance of getting an ace of hearts is:
1/13 x ¼ = 1/52