| The mother determines sex in humans | FALSE | The FATHER determines sex (he contributes X or Y; mother always contributes X) |
| Birds use the XX-XY sex determination system | FALSE | Birds use ZW-ZZ; female birds (ZW) are heterogametic |
| Klinefelter syndrome (47, XXY) individuals are female | FALSE | MALE — Y chromosome carries SRY gene which determines maleness |
| Turner syndrome (45, XO) individuals are male | FALSE | FEMALE — no Y chromosome present; default development is female |
| An affected male (Xh Y) can pass haemophilia to his sons | FALSE | He passes Y to sons; sons' X comes from mother. No father-to-son X-linked transmission |
| Sickle cell anaemia results from deletion of the HBB gene | FALSE | It results from a POINT MUTATION (single base change: GAG→GUG at codon 6) |
| Glutamic acid at position 6 of beta-globin is replaced by alanine in sickle cell | FALSE | It is replaced by VALINE (Val), not alanine |
| Thalassemia involves structurally abnormal haemoglobin | FALSE | Thalassemia involves REDUCED QUANTITY of normal globin chains (quantitative defect) |
| Alpha-thalassemia gene is on chromosome 11 | FALSE | Alpha-thalassemia (HBA) is on chromosome 16; chromosome 11 has HBB (beta-globin/sickle cell) |
| Down syndrome affects only females | FALSE | Down syndrome (trisomy 21, autosome) affects both males AND females |
| A carrier female for X-linked recessive is phenotypically affected | FALSE | Carrier female is phenotypically NORMAL (dominant allele masks recessive) |
| Super Female (47, XXX) individuals are always infertile | FALSE | Super Females are OFTEN FERTILE; unlike Turner females who have streak gonads |
| In autosomal recessive inheritance, the trait appears in every generation | FALSE | In autosomal recessive, the trait can SKIP generations when carriers mate with non-carriers |
| Two unaffected parents can produce an autosomal dominant offspring | FALSE | Autosomal dominant requires at least one dominant allele (at least one affected parent) |
| Males can be carriers for X-linked recessive disorders | FALSE | Males are hemizygous — they are either affected or unaffected, never carriers |
| The Barr body in Klinefelter (47, XXY) males = 1 | TRUE | Number of Barr bodies = X chromosomes - 1; XXY has 2 X chromosomes → 1 Barr body |
| PKU is treatable by early dietary intervention | TRUE | Low-phenylalanine diet from early infancy prevents intellectual disability in PKU |