Hey everyone,

Just prepping for my bio exam tomorrow and my prof and my TA still cant explain the difference between incomplete dominance and co-dominance that makes any sense to me, or that falls into place with what I know about bp morphs and genetics.

Heres what I think so far, and someone please tell me if I am wrong...

Incomplete dominance is when two traits are equally dominant and recessive, hence they are incomplete. For instance if XX is long and xx is Short, then Xx would be medium.....another example....RR is red, rr is whiteand Rr is pink. To me this seems to be a blending of the other two traits, but my prof keeps saying no, that the third trait/phenotype is intermediate between the other two, but despite half the class asking wtf he means by intermediate, he just says "look in your book", and I think we all know how textbooks try to teach.

Anyway, on to codom.

Prof says that the difference between codom and inc. dom is that in codom the third (or fourth, fifth, etc) trait is NOT intermediate between the other two, that it is entirely different. I was thinking, ok, this makes some sense....so I asked him how it would fall into a punnett square and he said again..look in your book it has great examples, yet there are no punnet squares for codom in it...so I asked if for instance there were only 3 traits/phenotypes that could be expressed, is it a codominant "trait" or set of traits that is controlled by one allele or does it take multiple alleles and it is how they arrange themselves together that you get the different traits.

So....here is what codom seems to be to me.

RR is red rr is white and Rr is white/red spotted (ie, with flowers and stuff) OR RR is red rr is white and Rr is yellow( or some other color), and that it is has nothing to do visually with the others, but it is just as dominant as the other two traits. If this is the case, in practice/probability, doesnt it present itself as being more dominant b/c having a het genotype is more common than being homozygous for either of the alleles?



I know it was long winded, and I hope someone can help. Thanks