Final answer:
Trinucleotide repeat diseases are caused by expansions of repeating sequences of three nucleotides within a gene. The proposed mechanism of expansion involves DNA replication errors during cell division.
Step-by-step explanation:
Trinucleotide repeat diseases are caused by expansions of repeating sequences of three nucleotides within a gene. The proposed mechanism of expansion involves DNA replication errors during cell division. These errors could result in the slippage of the DNA polymerase, leading to the addition of extra trinucleotide repeats in the newly synthesized DNA strand.
For example, in Huntington's disease, there is an expansion of CAG repeats in the huntingtin gene. This expansion leads to the production of mutant huntingtin protein, which is toxic to neurons and causes the symptoms of the disease.