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Outline 17- Genetics2

# Outline 17- Genetics2 - BSCI 106 Dr Sara Via Outline...

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BSCI 106 Fall 2008 p. 1 Dr. Sara Via Outline 18-Meiosis, Mitosis and Mendel #2 Test Cross Is an individual with the “dominant phenotype” a homozygote or a heterozygote? To find out, cross _______ x ________ Phenotypes of progeny clearly reveal the genotype of the unknown parent!! Know why it works that way!! One Locus: Incomplete Dominance Heterozygote has a distinct phenotype Usually, not always, intermediate What is the progeny phenotype ratio in intermediate dominance? Be sure you know what and WHY!! Using probabilities: expected phenotype ratio Punnett square gets complicated with 2 or more genes– too much bookkeeping! Can use probability to understand the outcome of any cross, if know 1. The probability of each possible gamete types 2. The probability of each possible progeny genotype Basic true facts about using probabilities 1. Probability ranges between 0 and 1 2.Probability of X = Prob(X) 3. Prob (X AND Y) = Prob (X) x Prob (Y) 4. Prob (X OR Y) = Prob (X) + Prob (Y) Using Probabilities Make this cross: Parents BB x bb F 1 all B b (WHY??) F 2 : cross two F 1 B b x B b F 1 gametes B b B b ½ ½ ½ ½ F 2 (progeny of F 1 ) genotypes: Prob( BB ) = ½ X ½ = ¼ (AND) Prob( B b + b B ) = ( ½ X ½) + (½ X ½ ) = ½ (AND) OR (AND)

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BSCI 106 Fall 2008 p. 2 Dr. Sara Via Prob(bb) = ½ X ½ = ¼ (AND) 1:2:1 Linkage: Alleles on same Chromosome No independent assortment (unless there is crossing over) Act just like one gene!
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