http://anthro.palomar.edu/mendel/ A nice site with more than u need to know.
Every trait is coded for twice in the DNA of most animals. Using for instance a gene for albinism...this trait is recessive. That means that the animal must inherit the gene from both parents.
The normal colouring gene is dominant...this means that only one copy of the normal gene is needed for it to be expressed.
This is why a "het (heterogenous) for albino" looks normal but can produce albino offspring if matted with and albino or another het. Hets are carriers of the gene. They have one copy of the dominant normal gene and one copy of the recessive albino gene.
This is a very basic view of genetics.
Codominance is best seen in blood types where we hav the O, the A and the B genes (or alleles). O is the recessive allele while neither the A or B alleles is dominant over the other...so they are called co-dominant.
If a person has 2 A alleles or one A and one O allele they hav blood type A.
If they have 2 B alleles or one B and one O they are blood type B.
If they have 2 O alleles they are blood type O (the recessive allele is O).
But if they have 1 A and 1 B they are blood type AB.
Hopefully that clears things up a bit?
