Probability and Genetics AP Biology Genetics and Probability

Probability and Genetics AP Biology

Genetics and Probability § Mendel’s laws Segregation Independent assortment § Reflect same laws of probability that apply to tossing coins or rolling dice AP Biology

Probability and Genetics § Calculating probability of making specific gamete is just like calculating probability in flipping a coin Probability of tossing heads? 50% Probability of making a P gametes… AP Biology

Probability and genetics § Outcome of 1 event has no impact on outcome of next event Probability of tossing heads each time? 50% Probability of making a P gamete each time? 50% AP Biology

Calculating Probability AP Biology

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 § Probability of Pp x Pp → pp AP Biology

Calculating dihybrid probability § Rule of multiplication also applies to dihybrid crosses Heterozygote parent –Yy. Rr Probability of producing yyrr? Probability of producing y gametes = ½ Probability of producing r gametes = ½ Probability of producing yr gametes = ½x½=¼ Probability of producing a yyrr offspring = ¼ x ¼ = 1/16 AP Biology

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 AP Biology

Using Chi Square in Genetics § Determining inheritance patterns § Example You propose that mutant trait in fruit flies is simple dominant inheritance set up cross between two true breeding flies Predict ratios of phenotypes expected from cross Establishes null hypothesis Any difference from these predicted results will be due to random chance you expect your observed experimental results to be the same as your expected prediction AP Biology

Using Chi Square in Genetics § After genetic cross is complete compare observed results against expected results Complete chi square analysis § If p value is greater than. 05 accept null hypothesis Differences are due to random chance alone genetic explanation for this trait is supported § If p value is. 05 or less reject null hypothesis Random chance alone can only explain differences fewer than 1 time out of every 20 Genetic explanation for this trait is unsupported Must consider alternative modes of inheritance AP Biology