zwenesky

I was studying single nucleotide polymorphism (SNP) and got really confused with the example of 4G/5G insertion/deletion polymorphism at -675 promoter region in Plasminogen activator inhibitor-1 gene. Does it mean 1G is present or absent in -675 position? What does it meant by 4G/4G, 4G/5G and 5G/5G genotypes? In case of deletion, if a G is missing in -675 position what's in there in place of that? Also, how is it possible to have 4G run in one allele and 5G in another allele for the same position? I'd really appreciate if anyone could shed some light and clear the concept here..what am i missing? Thank you!