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4/03/2012 Wednesday Do Now • Practice drawing a punnett square • Read explanation first • Do Monohybrid only • In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization • The true-breeding parents are the P generation • The hybrid offspring of the P generation are called the F1 generation • When F1 individuals self-pollinate, the F2 generation is produced Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 14-5-1 P Generation Purple flowers White flowers Appearance: Genetic makeup: PP pp Gametes: P p Fig. 14-5-2 P Generation Purple flowers White flowers Appearance: Genetic makeup: PP pp Gametes: p P F1 Generation Appearance: Genetic makeup: Gametes: Purple flowers Pp 1/ 2 P 1/ 2 p Fig. 14-5-3 P Generation Purple flowers White flowers Appearance: Genetic makeup: PP pp Gametes: p P F1 Generation Appearance: Genetic makeup: Gametes: Purple flowers Pp 1/ 2 1/ P 2 Sperm F2 Generation P p PP Pp Pp pp P Eggs p 3 1 p 3 Phenotype Genotype Purple PP (homozygous) Purple Pp (heterozygous) 1 2 1 Purple Pp (heterozygous) White pp (homozygous) Ratio 3:1 Ratio 1:2:1 1 Mendel used the scientific approach to identify two laws of inheritance 1. Law of Segragation (The “First Law”) : the two alleles of an individual for each trait separate (segregate) during gamete formation so that each gamete gets only one of the two allels Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Table 14-1 • Mendel identified his second law of inheritance by following two characters at the same time • Crossing two true-breeding parents differing in two characters produces dihybrids Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings EXPERIMENT P Generation YYRR yyrr Gametes YR yr F1 Generation YyRr Hypothesis of independent assortment Hypothesis of dependent assortment Predictions Sperm or Predicted offspring of F2 generation 1/ Sperm 1/ 1/ 2 2 YR 1/ YyRr YYRR 2 1/ 4 YR 1/ 4 1/ Yr 4 yR 1/ yr 4 YR YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr YR Eggs 1/ yr 2 4 1/ Yr 4 Eggs yr yyrr YyRr 3/ 4 1/ 1/ yR 4 4 Phenotypic ratio 3:1 1/ yr 4 9/ 16 3/ 16 3/ 16 Phenotypic ratio 9:3:3:1 1/ 16 Fig. 14-8b RESULTS 315 108 101 32 Phenotypic ratio approximately 9:3:3:1 2. Law of Independent Assortment (The “Second Law”) : member of each pair of alleles segregates independently of members of another pair of factors. Therefore, all possible contributions of factors can occur in gametes
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