Hi,
The length of the repeat does matter. e.g. generally speaking for CA
repeats they should at least 12 repeats long if they are to have a chance
of being polymorphic. Obviously this is the lowest limit and longer
repeats will have a increasing chance of being polymorphic and the longer
they are the better heterozygosity value you can get. The sequence of the
repeat should be perfect i.e. uninterupted by any imperfections. Imperfect
repeats (see SCA2) are not good substrates for replication slippage and
hence tend to be unpolymorphic.
ideally to summarise:
12 or more uninterupted repeat units and you are in with a chance!
hope this helps
cheers
Nick
