The red-green color blindness is a recessive X-linked trait. The females are not affected unless both the X chromosomes have the affected allele. Mostly, the females are the carriers, and the males are affected as they have only one X chromosome. In the given pedigree, the father of Irene have the normal allele, while her mother is a carrier. However, Irene is neither a carrier nor affected. This means that she carries normal alleles on both X chromosomes. Hence, her allele combination is [tex]X^{H} X^{H}[/tex] .
