Error: Klinefelter is female — WRONG. 47, XXY is MALE. The Y chromosome carries SRY gene, which overrides two X chromosomes and triggers male development. Extra X chromosomes do not determine female sex.

Error: Turner is male — WRONG. 45, XO is FEMALE. No Y chromosome means no SRY gene, so default female development occurs. XO individuals are female despite having only one sex chromosome.

Error: Father passes haemophilia to son — WRONG. Fathers pass Y chromosome to sons (not X). Sons can only receive an X-linked allele from their mother. Haemophilia in a son comes from the carrier or affected mother, never the father.

Error: P(haemophilic child) = 1/2 — WRONG in standard cross. In carrier female × normal male: P(haemophilic child) = 1/4. The 1/2 figure is P(haemophilic | given it's a son) — a conditional probability, not the overall probability.

Error: Sickle cell changes valine to glutamic acid — WRONG direction. Sickle cell changes GLUTAMIC ACID (normal, position 6) to VALINE (mutant). Normal = Glu; Sick = Val.

Error: Alpha-thalassemia is on chromosome 11 — WRONG. ALPHA-thalassemia = chromosome 16 (HBA genes). BETA-thalassemia and sickle cell = chromosome 11 (HBB gene).

Error: Males can be carriers for X-linked recessive disorders — WRONG. Males are hemizygous. They are either affected ($X^a$ Y) or normal ($X^A$ Y). The carrier heterozygous state ($X^A$ $X^a$) requires two X chromosomes and is only possible in females.

Error: Down syndrome affects only one sex — WRONG. Chromosome 21 is an AUTOSOME. Trisomy 21 affects both males and females equally.

Error: Birds use XX-XY system — WRONG. Birds use ZW-ZZ; the FEMALE (ZW) is heterogametic in birds. This is the reverse of humans.

Error: All daughters of affected XY father are affected (X-linked recessive) — WRONG. All daughters of an affected X-linked recessive father are CARRIERS (not affected), assuming the mother is a non-carrier ($X^A$ $X^A$). Daughters become carriers; sons are unaffected.