# The sum rule in probability applies when several

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The Sum Rule in Probability -Applies when several different events all give the same outcome -The probability that either event A or event B or event C will occur equals theprobability of A + B + C-Several different events all give the same total one could make a total of 7 from a 1 on the first die and a 6 on the second, or a 5 on the first and a 2 on the second, or a 4 on the first and a 3 on the second. -Each of these three combinations would be expected to occur at a frequency of 1/6 x 1/6 = 1/36-You should be able to see three more possible combinations that are just the opposite of the first three, that is, 6 on the first die and 1 on the second, and so on, for a total of six different ways to roll a 7 therefore, there are six waysof obtaining the same outcome. Therefore, for the probability of rolling a 7, we sum the individual probabilities to get the final probability: 1/36 + 1/36 +1/36 +1/36 +1/36 +1/36 = 6/36 = 1/6. Probability in Mendel’s Crosses -Randomness inherent in meiosis is comparable to the randomness inherent in rolling dice; the same rules of probability apply to genes carried on chromosomes in Mendel’s crosses -Punnett Square method for determining the genotypes and phenotypes of offspring and their expected proportions
10.1e Mendel Used a Testcross to Check the Validity of Hypothesis -Mendel crossed an F1plant with purple flowers, assumed to have heterozygous genotype Pp, with a true breeding white-flowered plant, with the homozygous genotype pp-There are two expected classes of offspring, Pp and pp, both with a probability of ½ the phenotypes of the offspring are expected to be 1 purple-flowered: 1 white-flowered-Mendel’s actual result closely approached the expected 1:1 ratio-Mendel also made the same type of cross with all the other traits used in his study, including those traits affecting seed shape, colour and plant height, andfound the same 1:1 ratio -A cross between an individual with the dominant phenotype and a homozygous recessive individual, such as the one described is called a testcross
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