Presuming that your question is not that cryptic and you want a serious
answer, and presuming that by "silent" you mean third codon positions, then
you are asking for a selective pressure, at other than the protein level,
which demands homozygosity.
Your best bets here are stem-loop (fold) pressure, GC-pressure and
AG-pressure. These may act in combination to make a selectively very stable
"James McInerney" <james.o.mcinerney at may.ie> wrote in message
news:9lu8dk$eqb$1 at mercury.hgmp.mrc.ac.uk...
> Hi all,
>> Cryptic question:
>> What would cause an excessively high number of silent sites being
> monomorphic in a population?