 # Mendelian Genetics What we learned Mendels contributions Mendelian

• Slides: 28 Mendelian Genetics: What we learned? Mendel’s contributions? Mendelian Genetics: What we learned? How many traits are considered for Aa. Bb. Cc Mendelian Genetics: What we learned? How many genotypic different gametes are produced by Aa. Bb. Cc? Mendelian Genetics: What we learned? What are the gametes produced by Aa. Bb? Mendelian Genetics: What we learned? What cross yields A-: aa 1: 1? What cross yields A-: aa 3: 1? What cross yields A-: aa 0: 1? Mendelian Genetics: What we learned? When are there only two phenotypes among the offspring? A cross yields a corn cob with 705 blue and 224 yellow kernels (blue>yellow). What is the genotype of the parents? (Or, what cross yielded these results? ) For a single-trait cross with dominant-recessive relationship between A and a: Consider monohybrid cross: Trait blue yellow total Expected Observed Consider test cross: Trait blue yellow total Expected Observed How do we evaluate difference between expected and observed? Trait Expected Observed blue 3 1500 yellow 1 500 total 4 2000 How do we evaluate difference between expected and observed? Trait Expected Observed blue 1 465 705 yellow 1 464 224 total 2 929 Expectations and observations may differ for two reasons: 1 st. Happy accidents. Expectations and observations may differ for two reasons: 1 st. Happy accidents. Expectations and observations may differ for two reasons: 2 nd The model is wrong. Expectations and observations may differ for two reasons: 2 nd The model is wrong. Calculate Chi-square: Calculate Chi-square: Example: Trait Blue yellow Total Expected 697 232 929 Observed 705 224 929 Calculate Chi-square: Example: Trait Blue yellow Total Expected 465 464 929 Observed 705 224 929 Calculate Chi-square: Example: Trait Red Pink White Expected Observed 225 400 215 Calculate Chi-square: Example: Trait Red Pink White Expected Observed 225 400 215 Calculate df = (n-1): Determine probability, P, for obtaining such a chi -square by chance alone: Determine probability, P, for obtaining such a chi -square by chance alone: When difference is small: When difference is large: Determine probability, P, for obtaining such a chi -square by chance alone: Example: chi-square: 0. 366 (df = 1) Determine probability, P, for obtaining such a chi -square by chance alone: Example: chi-square: 248 (df = 1) Determine probability, P, for obtaining such a chi -square by chance alone: Example: chi-square: 2. 14 (df = 2) 