Lecture 20 – Mendelian Genetics – Dihybrid Cross

Lecture 20 – Mendelian Genetics – Dihybrid Cross

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Lecture 20 – Mendelian Genetics – Dihybrid Cross A. Dihybrid cross (fig. 11-8) Principle of Independent Assortment - For independent assortment to occur, two or more traits are on nonhomologous chromosomes They are separated independently P: TTPP(tall, purple) x ttpp (short, white) TTPP can only produce one type of gamete (TP; no other combinations exist), ttpp can only produce one type of gamete as well (tp) F1: TtPp The phenotype is tall purple, and will look like TTPP Can produce four different types of gametes Foil the letters TtPp (first, outer, inner, last) and you get TP, Tp, tP, tp F2: TP Tp tP tp TP TTPP TTPp TtPP TtPp Tp TTPp TTpp TtPp Ttpp tP TtPP TtPp ttPP ttpp tp TtPp Ttpp ttPp tptp 9 T_P_ (tall purple) 3 T_pp (tall white) 3 ttP_ (short purple) 1 ttpp (tall white) Example: TtPP x ttpP
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tP tp TP TtPP TtPp tP ttPP ttPP 1 to 1 ratio, tall purple or short purple B. Extensions - Genetics isn’t always completely dominant or completely recessive 1. Incomplete dominance (fig. 11-18)
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Lecture 20 – Mendelian Genetics – Dihybrid Cross

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