(a) The trait is recessive (b) The trait is not sex - linked because it appears in male and in female.
(c) Both parents of Generation -I are heterozygous ( i.e., `Hb^(A)Hb^(S)`) and carrier for the gene. The 3rd child is male and developed the trait so the genotype is homozygous recessive (i.e., `Hb^(S), Hb^(S)`). The fourth child is female and carrier for the gene `(Hb^(A)Hb^(S))`