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Unformatted text preview: 1 26Sep09 Gardiner 1 Gregor Mendel Fig. 122, p. 236 B I O L O G Y 0 2 3 26Sep09 Gardiner 2 Mendel’s Law of Segregation • From monohybrid cross work • The two chromosomes of a homologous pair separate (are segregated) during metaphase I of meiosis I B I O L O G Y 0 2 3 26Sep09 Gardiner 3 Mendel’s Law of Independent Assortment • Comes from the dihybrid cross work • Independent assortment of alleles occurs as the various homologous pairs of chromosomes within a cell assort independently during anaphase I of meiosis I B I O L O G Y 0 2 3 26Sep09 Gardiner 4 Solving Mendelian Problems • Determine the simple probability of gamete genotype A – Aa P (A) = ½ – AA P (A) = 1 B I O L O G Y 0 2 3 26Sep09 Gardiner 5 Simple Probability • The probability of equally likely outcomes is • 1 • Number of possible outcomes • E.g. A coin toss has 2 possible outcomes • P (H) = P (T) = 1/2 B I O L O G Y 0 2 3 26Sep09 Gardiner 6 Solving Mendelian Problems • Determine the probability of gamete genotype AB – AaBb P (AB) = ¼ – Rule of multiplication  “A and B” 2 B I O L O G Y 0 2 3 26Sep09 Gardiner 7 Compound probability: multiplication rule • The probability of two independent events having a specified outcome is P 1 x P 2 • For example, a twocoin toss has four possible outcomes • ½ tails x ½ tails = ¼ double tails Multiplication Rule : If events A and B are independent, then P(A and B) = P(A)P(B) Suppose a six sided dice is rolled twice and the rolls are independent. A = rolling a 1 on the first roll B = rolling a 1 on the second roll P(rolling a 1 on both rolls) = P(A and B) =P(A)P(B) = 1/6 x 1/6 = 1/36 Segregation of alleles & fertilization as chance events B I O L O G Y 0 2 3 26Sep09 Gardiner 10 Dihybrid Cross • So: Parent YyRr • probability gamete will carry Y and R alleles is ¼ • In the F 2 we don’t have to construct a Punnett square – probability of YYRR is 1/16 ( ¼ chance ovum YR x ¼ chance YR sperm) B I O L O G Y 0 2 3 26Sep09 Gardiner 11 Compound probability : addition rule • The probability of alternative outcomes is P 1 + P 2 • For example, in a two coin toss, the probability that they will be the same is = ¼ double tails + ¼ double heads = 1 /2 B I O L O G Y 0 2 3 26Sep09 Gardiner 12 Solving Mendelian problems • Determine the probability of gamete genotype Ab or aB – AaBb P (Ab ) = 1/4 – AaBb P (aB ) = 1/4 – P (Ab or aB ) = 1/2 – Rule of addition “Ab or aB ” 3 PpYyRr x Ppyyrr What fraction of offspring will exhibit the recessive phenotype for at least two of the three traits? Pyr pyr PYR PPYrRr PpYyRr PYr PPYyrr PpYyrr PyR PPyyRr PpyyRr Pyr PPyyrr Ppyyrr pYR PpYyRr ppYyRr pYr PpYyrr ppYyrr pyR PpyyRr ppyyRr pyr Ppyyrr ppyyrr PpYyRr x Ppyyrr What fraction of offspring will exhibit the recessive phenotype for at least two of the three traits?...
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This note was uploaded on 04/18/2010 for the course BIOLOGY 1223 taught by Professor Gardiner/lajoie during the Spring '09 term at UWO.
 Spring '09
 GARDINER/LAJOIE
 Biology

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