If an individual is sensitized to the k antigen and has produced anti-k, what is her most probable Kell system genotype?

The presence of anti-k in an individual who is sensitized to the k antigen indicates that this person has been exposed to the k antigen and has developed an immune response against it. In the Kell blood group system, the K and k antigens are the two main antigens, where K is the dominant form, and k is the recessive form.

If a person has produced anti-k, it means that they do not express the k antigen on their red blood cells and therefore must have a genotype that does not include the k antigen. The only genotype that would fit this scenario is KK, as it would indicate homozygosity for the dominant allele that produces the K antigen, leading to a lack of expression of the k antigen.

The other genotypes—Kk (heterozygous, expressing both K and k) and kk (homozygous recessive, expressing only k)—cannot produce anti-k since either K or k is present. The genotype K0K0 (null genotype) indicates a lack of both K and k antigens, which would not lead to the production of anti-k. Therefore, the genotype KK is the only one that explains the sensitization to the k antigen and the production of anti-k.