<prompt> HbH is characterized by?Deletion of three alpha chain genesDeletion of three alpha chains and one beta chain genesDeletion of two alpha and two beta chain genesDeletion of four alpha chain genes  <response>: Alpha -Thalassemia Silent carrier state 1 gene deletion -a a a thalassemia trait 2 gene deletion -a-a HbH disease 3 gene deletion - - -a Hydrops fetalis 4 gene deletion - - - - 