Question

What mutation occurs to the FMR1 gene that causes fragile X syndrome?

a) Duplication of the gene
b) Deletion of the gene
c) Triplet repeat expansion
d) Inversion of the gene sequence

Answer 1

The mutation in the FMR1 gene causing fragile X syndrome is a triplet repeat expansion, with over 200 CGG repeats leading to methylation and silencing of the gene.

Step-by-step explanation:

The mutation that occurs to the FMR1 gene that causes fragile X syndrome is c) Triplet repeat expansion. Specifically, this genetic disorder is caused by a significant increase in the number of CGG trinucleotide repeats in the FMR1 gene, leading to methylation and silencing of the gene. A normal gene usually has about 5 to 40 repeats, whereas in fragile X syndrome, the affected gene may have over 200 CGG repeats. This expansion can impede the production of the fragile X mental protein (FMRP), which is crucial for normal neural development.