Which of the following disorders is associated with amplification of a trinucleotide repeat?

Fragile X syndrome is indeed associated with the amplification of a trinucleotide repeat, specifically the repetition of the CGG sequence in the FMR1 gene. This genetic mutation leads to the development of Fragile X syndrome, which is the most common inherited form of intellectual disability and also associated with various behavioral challenges. The increase in the number of CGG repeats can cause the gene to become unstable, leading to silencing of FMR1 and a deficiency of the fragile X mental retardation protein (FMRP), which is essential for normal neural development.

In contrast, the other disorders mentioned do not involve the amplification of a trinucleotide repeat. Sickle cell anemia results from a point mutation in the hemoglobin gene that leads to abnormal hemoglobin structure. Cystic fibrosis is caused by a deletion in the CFTR gene rather than a repeat expansion. Becker muscular dystrophy is linked to mutations in the dystrophin gene but does not involve trinucleotide repeats; it is typically characterized by deletions or duplications of DNA segments.

Understanding the genetic basis of these disorders highlights the specific nature of genetic mutations contributing to different diseases, where trinucleotide repeat expansions play a crucial role in conditions like Fragile X syndrome but not in others.