The allele expression in the case of a calico cat which shows both the trait for orange fur and black fur is Codominance.
Codominance is a hereditary model that states that in the heterozygous there is no recessive allele, but on the contrary, both alleles behave as dominant and both manifest themselves without mixing.
Codominance is an important aspect of the crossing process because the two allele genes are expressed, but not joined. An example of this is calico cats that have two X chromosomes in each of their cells.
In calico cats, the gene for the orange fur is located on the X chromosome and they have one allele for the black fur. The only way that both alleles occur together and combined with white is that there are two X chromosomes and these are codominant or these express at the same time.
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