Some proteins in body are usually not seen by immune system e.g. lens of eye. If eye is injured and lens protein gets into blood, antibodies are made to it. Diseases sometimes stimulate antibodies that can also react with a normal body protein e.g. rheumatic fever, in which antibodies against streptococcus later react with heart muscle proteins. But, some have the allele but not the disease. Lots of mutations.
Transitions are more common.
Can insert into any gene, usually destroying the gene. Microsatellites have 2 base repeats, can change number during cell division. Copy number cahnges in male meiosis but not female. One copy of the gene doesn't make enough product. Precursors build up in blood and cause dementia.