Inheritance Patterns Incomplete dominance Co dominance

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Transcript of Inheritance Patterns Incomplete dominance Co dominance

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Inheritance Patterns Incomplete dominance Co dominance Slide 2 Incomplete Dominance What happens when a true breeding red snapdragon (RR) crosses with a True breeding white snapdragon (R'R')? Snapdragon plants Slide 3 Result? p. 143 The F1 generation are all heterozygous (RR') Pink What happened to these traits? Did they blend? Slide 4 F2 generation yielded F1F1 F2F2 1 red: 2 pink: 1 white (different than that of Mendels F2 monohybrid cross ratio of 3:1) Slide 5 Conclusion: traits do not blend Explanation: Genes code for specific proteins Most are enzymes with different degrees of catalytic activity In this case, One allele (R) codes for an enzyme that produces red pigment Slide 6 Conclusion: traits do not blend The other allele (R') codes for an enzyme that does not produce pigment So, heterozygous plants (RR'), with only one allele for the functional enzyme produces just enough red pigment to display pink. (not completely dominant!) 2 alleles with functional enzymes (RR) produce enough pigment to show red Slide 7 Incomplete dominance A condition in which the heterozygous phenotype is intermediate between the 2 homozygous phenotypes We use RR' (not Rr) to indicate incomplete dominance Slide 8 Sample problem In four Oclock plants, red flowers are incompletely dominant over white flowers. The heterozygous flowers are pink. If a red-flowered four oclock plant is crossed with a white- flowered four oclock plant, what will be the flower colour of 1. The F 1 generation? Slide 9 Solution What is required? The flower colour of F1 generation? What is given? Red flowers (RR) incompletely dominant White flowers (R'R') Heterozygous flowers (RR') are pink Slide 10 Carry out solution RR'RR'RR'RR' RR'RR'RR'RR' R'R' R'R' R R The F1 generation is all pink Slide 11 Your turn In four Oclock plants, red flowers are incompletely dominant over white flowers. The heterozygous flowers are pink. If a red-flowered four oclock plant is crossed with a white- flowered four oclock plant, what will be the flower colour of The F1 generation crossed with its red parent? The F1 generation crossed with its white parent? Slide 12 Solution What is required? F1 (RR') X red parent (RR) F1 (RR') X white parent (R'R') What is given? Red flowers (RR) incompletely dominant White flowers (R'R') Heterozygous flowers (RR') are pink Slide 13 Results: RRR'RR' RRR'RR' RR'RR'R'R'R'R' RR'RR'R'R'R'R' RR'R' R R 2 red, 2 pink RR'R' R'R' R'R' 2 white, 2 pink Slide 14 Co dominance Sometimes, both alleles of a given characteristic are dominant Therefore, in heterozygotes, both alleles are expressed. Slide 15 I.e. Black rooster is crossed with a white hen Result? Black and white plumage Both colours were expressed Slide 16 Multiple alleles In addition to co dominance, Many genes may have multiple alleles: More than two alleles available to determine the phenotype of an organism I.e. co dominance & multiple alleles Slide 17 I.e. ABO blood group There are 3 different alleles for blood type: I A I B i Each type indicates a specific glycoprotein present on blood cells (People with type O have no glycoproteins on their blood cells) (People with AB have both types present) A is dominant to O B is dominant to O AB are both co dominant Slide 18 Slide 19 Sample problem If a woman has blood type AB, and a man has blood type A, what possible blood types will their children have? Slide 20 What is required? Possible blood types of children? What is given? Woman AB I A I B Man A I A I A or I A i Slide 21 Solution: IAIAIAIA IAIBIAIB IAIAIAIA IAIBIAIB IAIAIAIA IAIBIAIB IAiIAiIBiIBi I A I B IAiIAi 2 type A, 2 type AB2 type A, 1 type AB, 1 type B I A I B IAIAIAIA Slide 22 Your turn Suppose a man with blood type B marries a woman with type AB blood. What blood types would you expect to find among their children? What is required? Possible blood types of children What is given? Man I B I B or I B i Woman - I A I B Slide 23 Solution: IAIBIAIB IAIBIAIB IBIBIBIB IBIBIBIB 2 type AB, 2 type B IAIBIAIB IAiIAi IBIBIBIB IBiIBi 1 type AB, 2 type B, 1 type A I B I B i IAIBIAIB IAIBIAIB