- A Sickle cell anemia and cystic fibrosis, both caused by simple point mutations as frequently described
- B Huntington disease, myotonic dystrophy, fragile X syndrome (repeat tracts expand each generation)
- C Down syndrome and Turner syndrome, both caused by chromosome number changes overall in most textbook accounts
- D Mainly conditions following a generally autosomal recessive inheritance pattern during normal conditions
Correct answer: B. Huntington disease, myotonic dystrophy, fragile X syndrome (repeat tracts expand each generation)
Explanation: Trinucleotide repeat expansion diseases: unstable DNA repeats expand in meiosis. Show anticipation (worsening each generation). Examples: HD (CAG), FXS (CGG), DM1 (CTG).
Concept context
Mendel's laws, inheritance patterns, DNA structure, and molecular biology. Core of NEET biology.
Read the full Principles of Inheritance and Variation notes →