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Chapter 11 Independent Assortment, Segregation and an Introduction to Probability

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You Must Know The law of independent assortment and the law of segregation. (This is review from last chapter.) The addition and multiplication rules. (You will get more practice using these later.)

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Independent Assortment of Chromosomes Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1Combination 2Combination 3Combination 4 The number of combinations possible when chromosomes assort independently into gametes is 2 n, where n is the haploid number.

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YRyr YR yr YYRR yyrr YyRr Experiment showing independent assortment. Predictions P Generation F 1 Generation Predicted offspring in F 2 generation Gametes YYRR yyrr YyRr Results Eggs Sperm or Hypothesis of dependent assortment Phenotypic ratio 3:1 Hypothesis of independent assortment ¾ ¼ ½ ½ ½ ½ ¼ ¼ ¼ ¼ ¼¼ ¼ ¼ YR yr Phenotypic ratio approximately 9:3:3:1 Phenotypic ratio 9:3:3:1 YR yr YR yr YYRR yyrr YYRr YyRr YryR Yr yR YyRR YYRrYYrr Yyrr YyRr YyRRYyRr yyRr yyRR YyRrYyrr yyRr dihybrid

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Duplicated pair of homologous chromosomes Pair of homologous chromosomes in diploid parent cell Chromosomes duplicate Diploid cell with duplicated chromosomes Homologous chromosomes separate Sister chromatids separate Meiosis I Meiosis II Haploid cells with unduplicated chromosomes 1 2 Law of segregation: The two alleles for each character separate from each other during gamete formation.

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R r R r R r Segregation of alleles into eggs Eggs Sperm ¼ ½½ ½ ½ Segregation of alleles into sperm Rr R R ¼ r r ¼ R r ¼ The multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities. Ex. (1/2)(1/2)=1/4 There is a 25% chance that you will get RR.

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R r R r R r Segregation of alleles into eggs Eggs Sperm ¼ ½½ ½ ½ Segregation of alleles into sperm Rr R R ¼ r r ¼ R r ¼ The addition rule states that the probability that any one of two or more mutually exclusive events will occur is calculated by adding together their individual probabilities. Ex. ¼ + ¼ = ½ or There is a 50% chance that you will get RR or rr.

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