A. Complete Dominance: When the phenotype of the heterozygote and the homozygote are the same we have complete dominance.

B.Incomplete Dominance: When a hetrozygote is phenotypically intermediate between the two homozygotes.
It occurs when both copies of a functional allele are necesary in order to produce enough protein to give rise to the dominant phenotype.

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E.g. Snapdragon Flowers

C. Codominance: Mutations can give rise to different versions of a gene. So you can have multiple alleles for a given gene. codominance is when both phenotypes are expressed. More >>

E.g. Blood type in humans.

There are three alleles for the gene that codes for blood type, A B O.

The possible combinations of alleles are I^AI^A, I^Ai, I^AI^B, I^BI^B, I^Bi, ii

ii = blood type O
I^Ai = blood type A
I^Bi = blood type B
I^AI^B = blood type AB
I^AI^A = blood type A
I^BI^B = blood type B

What possible offspring could you get from an A type female and a B type female mating?

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Key terms:

Basic facts: