the hemoglobin b gene (hb) has a common allele (a) of a snp (rs334) that encodes the hba form of adult hemoglobin and a rare allele (t) that encodes the sickling form of hemoglobin, hbs. among 57 members of the yoruba tribe of nigeria, 44 were a/a and 13 were a/t. no t/t individuals were observed. use the chi-square test to determine whether these observed genotypic frequencies fit hardy-weinberg expectations. (critical value of 3.81 at p