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Mendelian Genetics. Chapter 10 Human karyotype Gene • basic unit of inheritance • a heritable factor that controls a specific characteristic • a given number of bases in a DNA strand • all the genes of an organism are known collectively as the genome Chromosomes Alleles Locus • the position of a gene on a chromosome Mendelian Genetics R = round seed r = wrinkled seed Mendel’s 1st cross: (this is a test cross- individual is crossed with a homozygous recessive in order to see what the parent is) R R r Rr Rr r Rr Rr Mendel’s 2nd cross: R r R RR Rr r Rr rr Mendel’s 3rd cross: R R R RR RR R RR RR r r r rr rr r rr rr R r R RR Rr r Rr rr Mendel’s First Law (Law of Segregation) Mendel’s Second Law (Independent Assortment) Statistical Testing • Used by biologists to find out if observed results differ significantly from expected results. • Biologists want more than 95% confidence which means the probability that the deviation of the observed from that expected is due to chance alone (no other forces acting). • In a genetic experiment, it can be used to decide if observed data fits any of the expected Mendelian ratios or if data is too “far off” and should be rejected. Observed Values Expected Values 315 Round, Yellow Seed 108 Round, Green Seed 101 Wrinkled, Yellow Seed (9/16)(556) = 312.75 Round, Yellow Seed (3/16)(556) = 104.25 Round, Green Seed (3/16)(556) = 104.25 Wrinkled, Yellow (1/16)(556) = 34.75 Wrinkled, Green 32 Wrinkled, Green 556 Total Seeds 556.00 Total Seeds • • • • X2 = 0.47 (this is the answer, do not √ it) Find the correct critical value on the following table. Find the degrees of freedom (n-1) in your data. If calculated chi-square is lower than the critical value, this shows there is no significant difference between the expected and observed values and the results are within the range of acceptable deviation. • If it is above, the difference is too great and the results are outside the range of acceptable deviation and should be rejected! Degrees of Freedom (df) 1 2 3 4 5 6 7 8 9 10 Probability (p) 0.95 0.90 0.80 0.70 0.50 0.30 0.20 0.10 0.05 0.01 0.001 0.004 0.02 0.06 0.15 0.46 1.07 1.64 2.71 3.84 6.64 10.83 0.10 0.21 0.45 0.71 1.39 2.41 3.22 4.60 5.99 9.21 13.82 0.35 0.58 1.01 1.42 2.37 3.66 4.64 6.25 7.82 11.34 16.27 0.71 1.06 1.65 2.20 3.36 4.88 5.99 7.78 9.49 13.28 18.47 1.14 1.61 2.34 3.00 4.35 6.06 7.29 9.24 11.07 15.09 20.52 1.63 2.20 3.07 3.83 5.35 7.23 8.56 10.64 12.59 16.81 22.46 2.17 2.83 3.82 4.67 6.35 8.38 9.80 12.02 14.07 18.48 24.32 2.73 3.49 4.59 5.53 7.34 9.52 11.03 13.36 15.51 20.09 26.12 3.32 4.17 5.38 6.39 8.34 10.66 12.24 14.68 16.92 21.67 27.88 3.94 4.86 6.18 7.27 9.34 11.78 13.44 15.99 18.31 23.21 29.59 Significant. Reject! Differences are NOT due to chace Nonsignificant. The differences are do to acceptable chance. Do NOT reject without other cause