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Unformatted text preview: 40 Chapter 2 Patterns of Inheritance the die has six sides and only one side carries the 4. This probability is written as follows: Therefore, with the use of the product rule, the probability of a 4 appearing on both dice is , which is written Now for the sum rule: p (of two 4 9 s) 5 1 6 3 1 6 5 1 36 1 6 3 1 6 5 1 36 p (of a 4) 5 1 6 Therefore, the overall probability (or expected fre- quency) of progeny of genotype a / a ; b / b ; c / c ; d / d ; e / e will be . So we learn that we need to examine 200 to 300 hundred progeny to stand a chance of obtaining at least one of the desired genotype. This probability calculation can be extended to predict phenotypic frequencies or gametic frequencies. Indeed, there are thousands of other uses for this method in genetic analysis, and we will en- counter many in later chapters. USING THE CHI-SQUARE ( x 2 ) TEST ON MENDELIAN RATIOS In genetics generally, a researcher is often con- fronted with results that are close to but not identical with an expected ratio. But how close is enough? A sta- tistical test is needed to check such ratios against expec- tations, and the chi-square test fulfills this role....
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.
- Spring '08