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Inheritance Patterns Incomplete dominance Co dominance.

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Presentation on theme: "Inheritance Patterns Incomplete dominance Co dominance."— Presentation transcript:

1 Inheritance Patterns Incomplete dominance Co dominance

2 Incomplete Dominance What happens when a true breeding red snapdragon (RR) crosses with a True breeding white snapdragon (R'R')? Snapdragon plants

3 Result? p. 143 The F1 generation are all heterozygous (RR') Pink What happened to these traits? Did they blend?

4 F2 generation yielded… F1F1 F2F2 1 red: 2 pink: 1 white (different than that of Mendel’s F2 monohybrid cross ratio of 3:1)

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

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

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

8 Sample problem In four O’clock plants, red flowers are incompletely dominant over white flowers. The heterozygous flowers are pink. If a red-flowered four o’clock plant is crossed with a white- flowered four o’clock plant, what will be the flower colour of 1. The F 1 generation?

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

10 Carry out solution… RR'RR'RR'RR' RR'RR'RR'RR' R'R' R'R' R R The F1 generation is all pink

11 Your turn… In four O’clock plants, red flowers are incompletely dominant over white flowers. The heterozygous flowers are pink. If a red-flowered four o’clock plant is crossed with a white- flowered four o’clock plant, what will be the flower colour of The F1 generation crossed with its red parent? The F1 generation crossed with its white parent?

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

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

14 Co dominance Sometimes, both alleles of a given characteristic are dominant Therefore, in heterozygotes, both alleles are expressed.

15 I.e. Black rooster is crossed with a white hen Result? Black and white plumage Both colours were expressed

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

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

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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?

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

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

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

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


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