Sickle-cell anaemia is an autosome linked recessive trait. It is controlled by alleles and . Only homozygous individuals for () show the diseased phenotype, while heterozygous individuals () are carriers . In a cross between two heterozygous parents ( x ), the resulting genotypes in the progeny are 25% (normal), 50% (carrier), and 25% (diseased). Therefore, 25% of the progeny will be diseased.