Mutations are changes which occur in a (i) or a (ii) If a mutation occurs in a cell which is going to form a (iii) the mutation may affect the whole (iv) which develops. Down syndrome results from a (v) mutation in the (vi)

Correct Answer: B

Rationale: Mutations occur in genes or chromosomes. Germline mutations (gametes) affect the whole organism. Down syndrome is a chromosomal mutation (trisomy 21). Correct sequence: B, D, C, E, D, D.

Correct Answer: A

Rationale: Hemophilia is X-linked recessive, unlike PKU, cystic fibrosis (autosomal recessive), and achondroplasia (autosomal dominant).

Correct Answer: D

Rationale: Mitochondria are maternally inherited via the egg; sperm contribute negligible mitochondrial DNA.

Correct Answer: A

Rationale: Cancer cells lose contact inhibition (normal cells stop dividing when touching), enabling uncontrolled growth.

Correct Answer: A

Rationale: Tumor suppressor genes (e.g., RB, p53) inhibit cell division to prevent cancer.