Final answer:
The partially mutated FMR1 gene, also known as a premutation, is characterized by having 70-90 CGG trinucleotide repeats.
Step-by-step explanation:
The number of trinucleotide repeats that represents a partially mutated FMR1 gene (premutation) is c) 70-90 repeats. The FMR1 gene is associated with Fragile X syndrome, and the number of CGG repeats affects the gene's expression. A fully mutated gene typically contains over 200 repeats, leading to the silencing of the gene and the development of Fragile X syndrome. However, premutations fall in the range of approximately 55 to 200 repeats, where the gene is partially affected. These premutations can lead to some clinical symptoms and are also prone to expand in subsequent generations, which could eventually lead to a full mutation.