Presentation on theme: "Incomplete dominance Co dominance"— Presentation transcript:
1 Incomplete dominance Co dominance Inheritance PatternsIncomplete dominanceCo dominance
2 Incomplete DominanceSnapdragon plantsWhat happens when a true breeding red snapdragon (RR)crosses with aTrue breeding white snapdragon (R'R')?
3 Result? The F1 generation are all heterozygous (RR') Pink What happened to these traits? Did they blend?p. 143
4 F2 generation yielded… F1 F2 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 proteinsMost are enzymes with different degrees of catalytic activityIn 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 pigmentSo, 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 dominanceA condition in which the heterozygous phenotype is intermediate between the 2 homozygous phenotypesWe use RR' (not Rr) to indicate incomplete dominance
8 Sample problem The F1 generation? 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 ofThe F1 generation?
9 Solution What is required? What is given? The flower colour of F1 generation?What is given?Red flowers (RR) incompletely dominantWhite flowers (R'R')Heterozygous flowers (RR') are pink
10 Carry out solution…R'R'RR'RRThe F1 generation is all pink
11 Your turn… The F1 generation crossed with its red parent? 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 ofThe F1 generation crossed with its red parent?The F1 generation crossed with its white parent?
12 Solution What is required? What is given? F1 (RR') X red parent (RR) F1 (RR') X white parent (R'R')What is given?Red flowers (RR) incompletely dominantWhite flowers (R'R')Heterozygous flowers (RR') are pink
13 Results: R R' R R' RR RR' RR' R'R' R' R R R' 2 red, 2 pink 2 white, 2 pink
14 Co dominanceSometimes, both alleles of a given characteristic are dominantTherefore, in heterozygotes, both alleles are expressed.
15 I.e. Black rooster is crossed with a white hen Result?Black and white plumageBoth 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 organismI.e. co dominance & multiple alleles
17 I.e. ABO blood group A is dominant to O B is dominant to O There are 3 different alleles for blood type:IAIBiEach 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 OB is dominant to OAB are both co dominant
19 Sample problemIf 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? What is given? Possible blood types of children? Woman AB IAIBMan A IAIA or IAi
21 Solution: IAIA IAIB IAIA IAIB IAi IBi IA IB IA IB IA IA i 2 type A, 2 type AB2 type A, 1 type AB, 1 type B
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 childrenWhat is given?Man – IBIBor IBiWoman - IAIB
23 Solution: IAIB IBIB IAIB IAi IBIB IBi IB IB IB i IA IA IB IB 2 type AB, 2 type B1 type AB, 2 type B, 1 type A