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!

It indeed refers to the insertion or deletion of a base at that position (so either absence or presence of an additional G) on the respective chromsome (remember, we are diploid).

I think you are looking at it from a A-B perspective. Add X-Y to the equation and you will get your answer

If that was supposed to mean that it somehow involves sex chromosomes, then no. PAI is on chromosome 7.

SERPIN PEPTIDASE INHIBITOR, CLADE E (NEXIN, PLASMINOGEN ACTIVATOR INHIBITOR TYPE 1), MEMBER 1; SERPINE1
PLASMINOGEN ACTIVATOR INHIBITOR 1; PAI1 aka PLANH1, SERPINE1
ENDOTHELIAL PLASMINOGEN ACTIVATOR INHIBITOR
HGNC Approved Gene Symbol: SERPINE1
Cytogenetic location: 7q22.1 Genomic coordinates (GRCh37): 7:100,770,369 - 100,782,546

 

 

This protein encoding appears to be structural. It does not appear to have enzymatic or interactive properties.

 

4G/4G, 4G/5G and 5G/5G is referring to homozygous recessive, heterozygous and homozygous dominant -- respectively. The "blonde" type may see transient thrombophiliae which is not life threatening but apparently characteristic. It would seem this is the "thinner skinned" type. This person would be....mmm....I'll guess less stable? Or more stable depending on prospectives.

 

The polymophism referred to is a genetic anomaly. This protein, in this case, is not coded to contain an end point. The genetic mechanics will not be able to complete this protein. The protein is presumed to be non-functional, perhaps residual.

Edited September 30, 201312 yr by vampares

First of all, as the name it implies it is is not a structural protein but an inhibitor of a serine protease. Also polymorphisms are not anomalies, there are simply genetic variants of a particular gene. The vast majority of existing alleles are do not result in dysfunctional proteins, as they would likely be selected against and thus eliminated from the population. Allelic variants can have different properties in terms of expression or activities, though.