1. Chapter 4 Probability and Heredity
Section 2

2. I can… explain the role of probability in a genetic cross
Warm Up: If a mother rabbit is hybrid for black fur, and black fur is dominant, how would you write her alleles?
Wrap Up: Draw a punnett square for the cross: Hh x Hh

3. Principles of Probability
Probability: the number that describes how likely it is that an event will occur
Coin toss: two possible ways that the coin will land (heads up or tails up)
1 in 2 chance, ½, 50%
The Laws of Probability predict what is LIKELY to occur

4. Independence of Events
When you toss a coin more than once, the results of one toss do not affect the results of the next toss

5. Principles of Probability with Genetics
Mendel realized that the mathematical principles of probability applied to his work
He could say that the probability of producing…
A tall plant was 3 in 4
A short plant was 1 in 4
HOW?!

6. Something called…. PUNNETT SQUARES
Punnett square: a chart that shows all the possible combinations of alleles that result from a genetic cross
They show all the possible outcomes of a genetic cross and determine the probability of that outcome

7. Example RR Rr rr R r R r Hybrid (one dominant, one recessive)
R: round seed (dominant)
r: wrinkled seed (recessive) R r RR Rr rr R r

8. Using a Punnett Square
Use a Punnett square to calculate the probability
In a genetic cross, the allele that each parent will pass on to its offspring is based on probability

9. What is the probability that the offspring will be RR?
25% or 1 in 4
What is the probability that the offspring will be rr?
What is the probability that the offspring will be Rr?
50% or 2 in 4
What is the probability that the offspring will be a round seed?
75% or 3 in 4
What is the probability that the offspring will be a wrinkled seed?

10. Predicting Probabilities
Dominant: black fur
Recessive: white fur
What are the possible allele combinations? Bb
What is the probability the guinea pig has black fur?
100%

11. Phenotypes and Genotypes
Phenotype: physical appearance, or visible traits
Genotype: genetic makeup, or allele combination
What is the dominant trait?
Smooth pods
What is the recessive trait?
Pinched
How many different
phenotypes? How many
different genotypes?

12. Homozygous and Heterozygous
Purebred = two identical alleles = homozygous
SS or ss
Hybrid = two different alleles = heterozygous Ss

13. Codominance
Codominance: the alleles are neither dominant nor recessive
Both results are expressed in the offspring, black and white feathers
Will the offspring be heterozygous? Or homozygous?