"Heterozygotic expection" - when heterozygote differs from both homozygotes, but homozygotes are similar

Question

For simple 2-alleles genetic model {a,A} and corresponding quantitative trait Q is typically true that

Q(aa)>=Q(aA)>=Q(AA)

or conversely

Q(AA)>=Q(aA)>=Q(aA).

For example, dominance means that Q(aa) < Q(aA)=Q(AA) , recesivity Q(aa)=Q(aA) < Q(AA) ; in additive models Q(aa) < Q(aA) < Q(AA) etc.

The situation when Q(aA)>Q(aa)~Q(AA) is atypical in biology ("heterozygotic expection ?", "uncooperative alleles ?"). Known example is HBB gene (heterozygotic form gives resistence to malaria but homozygotic mutation form is sickle-cell anaemia). But this is weak example only, because f is evolutionary advantage, not a measurable phenotypical or biochemical trait.

QUESTION 1: Are there any systematic reviews about this atypical phenomena? (about "heterozygotic expection")

QUESTION 2: Is there a standard scientific term for this phenomena?

Answer 1

You question is a bit unclear, and I think there might be a couple of mistakes in your inequalities. However, I think you are looking for the terms Overdominance (also called Heterozygote advantage) and Heterosis (also Hybrid vigor). Both of these concepts imply that heterozygotes and/or hybrids have a phenotype that lies outside of the range described by the homozygotes (or, for heterosis, either parent or parent population).

Here is a section from "Genetic Dominance: Genotype-Phenotype Relationships" from Nature education - Scitable, which has a bit more information and a couple of references:

In particular, the phenomenon known as overdominance occurs when a heterozygote has a more extreme phenotype than that of either of its parents. Indeed, in a few examples, a trait that shows overdominance sometimes confers a survival advantage in the heterozygote (Parsons & Bodmer, 1961).

You will find more information about overdominance and heterosis in any textbook on evolutionary biology, e.g. Futuyma's Evolution. There are also lots of relevant papers on the subject, and this one might be a nice example and starting point:

Frascaroli et al. 2007. Classical Genetic and Quantitative Trait Loci Analyses of Heterosis in a Maize Hybrid Between Two Elite Inbred Lines. Genetics 176(1): 625-644.