1. Chapter 6: Introduction to Genetics
Section 6-3:
Analyzing Inheritance (Probability)

2. Punnett Squares = Predictors
Punnett squares are used to determine the likely genotypes of offspring, if we know the parental genotypes
Simply a prediction, showing the probability of certain genotypes and phenotypes in offspring

3. Probability Think about flipping a coin . . .
You have a ½ chance of getting heads or tails for each trial – this is probability
If you flip a coin four times in a row, the probability of getting heads each time is . . .
½ x ½ x ½ x ½ = 1/16
Each flip is an independent event – past outcomes do not influence future outcomes

4. Probability and Genetics
The formation of gametes (sex cells) depends on random events
When alleles are segregated, there is a ½ chance of each gamete receiving each allele
This random nature of segregation is why probability can be applied to genetics

5. Let’s Practice!
In fruit flies, the allele for gray body (G) is dominant over the allele for black body (g). In a cross between a black fruit fly and a heterozygous gray fruit fly, what is the probability that one offspring will have a gray body? That two offspring will have gray bodies?
Answer: One offspring = ½, two offspring = ¼