Chapter 6: Introduction to Genetics

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