What is incomplete autosomal dominant inheritance?
• In its simplest form, it involves 1 pair of genes with the wild type/normal gene "a" being recessive to the mutant/dominant gene "A". Since the mutation is incomplete or not fully dominant, a combination of the two gene types will result in an intermediate form between the wild type and mutant forms. If the wild type/natural colour of a bird is green and the mutant form is dark green, the following will be true:
+ kk = Green Bird
+ Kk = Medium Green Bird
+ KK = Dark Green Bird
• In the following example, one gene, we will call it "K", is responsible for colour. The "K" gene comes in 2 forms: "K" and "k". When the "K" gene is a capital "K", it is responsible for the dark green colour and classified as dominant. When the "K" gene is a small "k", it is responsible for the regular/wild type green colour and is classified as recessive. The are always 2 copies of the "K" gene in each individual. If an individual is kk, then it is green/normal/wild type or is a homozygote (the pair of genes are the same) for the green gene. Green is the recessive form. If an individual is KK, then it is dark green or in its dominant form. "KK" is a homozygote for the dark green gene. Most autosomal dominant mutations are incomplete (as is this one) meaning that the heterzygote has a different phenotype (or appearance) than both the homozygous dominant form (KK) and the homozygous recessive for (kk). The phenotype for a Kk individual is a mix of the dark and regular/light green colours resulting in a medium green bird. It is still a heterozygote, but it appears almost as a new mutation since it is a different colour than the wild type form and full mutation.
"K" = dark green gene
"k" = green gene
KK = dark green individual
Kk = medium green / heterozygous individual
kk = green individual
(1) Dark Green (KK) X Dark Green (KK) = All Dark Green (KK)
K K KK KK K KK KK
K
(2) Green (kk) X Green (kk) = All Green (kk)
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k |
k |
k
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kk |
kk |
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k |
kk |
kk |
(3) Dark Green (KK) X Green (kk) = All Medium Green/Heterozygotes (Kk)
K K Kk Kk k Kk Kk
k
(4) Medium Green/Heterozygotes (Kk) X Medium Green/Heterozygotes (Kk) = 25% Dark Green (KK), 50% Medium Green/Heterozygotes (Kk), & 25% Green (kk)
K k KK Kk k Kk kk
K
(5) Medium Green/Heterozygotes (Kk) X Dark Green (KK) = 50% Dark Green (KK) & 50% Medium Green/Heterozygotes (Kk)
K k KK Kk K KK Kk
K
(6) Medium Green/Heterozygotes (Kk) X Green (kk) = 50% Medium Green/Heterozygotes (Kk) & 50% Green (kk)
K k Kk kk k Kk kk
k
