Incomplete dominance Co dominance Inheritance Patterns Incomplete dominance Co dominance

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

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

F2 generation yielded… F1 F2 1 red: 2 pink: 1 white (different than that of Mendel’s F2 monohybrid cross ratio of 3:1)

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

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

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

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 of The F1 generation?

Solution What is required? What is given? The flower colour of F1 generation? What is given? Red flowers (RR) incompletely dominant White flowers (R'R') Heterozygous flowers (RR') are pink

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

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 of The F1 generation crossed with its red parent? The F1 generation crossed with its white parent?

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 dominant White flowers (R'R') Heterozygous flowers (RR') are pink

Results: R R' R R' RR RR' RR' R'R' R' R R R' 2 red, 2 pink 2 white, 2 pink

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

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

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

I.e. ABO blood group A is dominant to O B is dominant to O There are 3 different alleles for blood type: IA IB 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

Sample problem If a woman has blood type AB, and a man has blood type A, what possible blood types will their children have?

What is required? What is given? Possible blood types of children? Woman AB IAIB Man A IAIA or IAi

Solution: IAIA IAIB IAIA IAIB IAi IBi IA IB IA IB IA IA i 2 type A, 2 type AB 2 type A, 1 type AB, 1 type B

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 – IBIBor IBi Woman - IAIB

Solution: IAIB IBIB IAIB IAi IBIB IBi IB IB IB i IA IA IB IB 2 type AB, 2 type B 1 type AB, 2 type B, 1 type A