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Law of Independent Assortment

Bi 2g,3a,3b. Law of Independent Assortment. Monohybrid cross. Some of Mendel’s experiments followed the inheritance of single traits flower color seed color monohybrid crosses. Dihybrid cross. Other of Mendel’s experiments followed the inheritance of 2 different traits

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Law of Independent Assortment

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  1. Bi 2g,3a,3b Law of Independent Assortment

  2. Monohybrid cross • Some of Mendel’s experiments followed the inheritance of single traits • flower color • seed color • monohybrid crosses

  3. Dihybrid cross • Other of Mendel’s experiments followed the inheritance of 2 different traits • seed color andseed shape • dihybrid crosses Mendelwas working outmany of the genetic rules!

  4. YR YR yR Yr yr yr YyRr What’s going on here? • If genes are on different chromosomes… • how are they passed on to the gametes? • together or independently? Is it this? Or this? YyRr Which systemexplains the data?

  5. F1 generation (hybrids) yellow, round peas 100% F2 generation Dihybrid cross P true-breeding yellow, round peas true-breeding green, wrinkled peas x YYRR yyrr Y = yellow R = round y = green r = wrinkled YyRr self-pollinate 9:3:3:1 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas

  6. 9/16 yellow round YyRr YyRr 3/16 green round YR YR yr YR yR Yr yr Yr 3/16 yellow wrinkled yR 1/16 green wrinkled yr Dihybrid cross or YyRr x YyRr YR Yr yR yr  YYRR YYRr YyRR YyRr BINGO! YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr

  7. yellow green round wrinkled Mendel’s 2nd law of heredity Can you thinkof an exceptionto this? • Law of independent assortment • different genes separate into gametes independently • non-homologous chromosomes align independently • classes of gametes produced in equal amounts • YR = Yr = yR = yr • only true for genes on separate chromosomes or on the same chromosome YyRr Yr Yr yR yR YR YR yr yr 1 : 1 : 1 : 1

  8. Metaphase 1 Law of Independent Assortment • Which stage of meiosis creates the law of independent assortment? RememberMendel didn’teven know DNA—or genes—existed! EXCEPTION • If genes are on same chromosome & close together • will usually be inherited together • rarely crossover separately • “linked”

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