Answer: Huntington disease, myotonic dystrophy, fragile X syndrome (repeat tracts expand each generation).
- 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).
Punnett square for a monohybrid cross between two heterozygous (Tt) parents, showing the 3:1 phenotypic ratio predicted by Mendel's Law of Segregation.
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 →