Keisha has inherited one recessive gene for the sickle-cell trait along with one normal dominant gene. as a result of this incomplete dominance she is resistant to malaria and does not have sickle-cell anemia
Keisha have a dominant gene which should be expressed over the recessive gene. But the gene is not fully expressed. This condition could happen because the gene incomplete dominance, which make it not fully expressed if there is only one gene. The result of heterozygotes would be less than homozygote dominant.