by the same token, he recognized that ascertainment was responsible for a phenomenon known as anticipation, the tendency for a genetic disease to manifest earlier in life and with increased severity in later generations. weinberg recognized that this was because those later generations were the offspring of that selected group of earlier carriers that had successfully reproduced. subsequent researchers have reasoned that such carriers who reproduce might be expected to carry favorable compensatory mutations that allowed them to reproduce successfully in spite of their disease. in a class of autosomal and x-linked dominant diseases known as trinucleotide repeat disorders (for example, huntington's disease), a molecular mechanism for anticipation has also been demonstrated. it is caused by the instability of repeating nucleotide sequences that tend to undergo expansion, causing disease at an earlier and earlier age as trinucleotide repeats accumulate.