As I understand it, co-dominance is when both genes in an allelomorphic pair produce both their effects equally on the organism in question whilst incomplete dominance applies to an instance where a mix of the effects of two alleles are present — i.e. where one allele is not completely masked by the other.
However, I had this notion challenged by the following paragraph I obtained from a reputable online source:
Carnation plants show co-dominance for the anthocyanin gene. There are two alleles:
$F^A$ – allele for anthocyanin pigment (red flowers)
$F^N$ – allele for no anthocyanin pigment (white flowers)
[...] a carnation plant heterozygous for this gene would yield pink flowers [...]
Shouldn't the phenotype of the flower be red and white as opposed to being pink, as the alleles have been said to exhibit co-dominance? Anything I am probably missing out on?
I have bountied this question because I think I have a major hole with my understanding on this topic somewhere; to give you some perspective, I am a High-School Sophomore currently on an introductory course in Mendelian Genetics/Inheritance. I read through @swbarnes2's answer where they say:
In the case of flowers, if you have two different alleles for the same pigment gene, you will see a blending, because all the pigment-making cells will produce from both alleles.
In such a case (if this always happens), where do the ideas of codominance and incomplete dominance come in? According to my textbook, the following terms are defined as:
If both genes of an allelomorphic pair produce their effects in an individual (i.e neither allele is dominant to the other) the alleles are said to be co-dominant.
Incomplete dominance applies to a case where the effect of the recessive allele is not completely masked by the dominant allele (in this case, I assume, a blending would occur)
(I do get that this may not apply to carnation plants, but would it be safe to follow the phenotypes predicted by my textbook definitions for all other cases?)
Hope someone could clear my doubt; I am extremely confused to read (in the comments section) why co-dominance would not mean both colors/phenotypes are shown simultaneously — like being red and white (as opposed to them mixing into pink).