Meaning of the P-value relating to SNP (single nucleotide polymorphism)

[nhaus]

Hey guys,
im relatively new to the subject and coundnt find a proper answer to my question in the internet yet... :/
I am currently trying to understand a paper about Genom wide association studies (GWAS) and they constantly talk about p-values of SNP.

And i just dont understand what the p value is telling me in that context...
I hope you guys can help me!

[mastal]

The probability that the SNP is associated with a particular disease.

[nhaus]

and the lower the p value the more likely it is that this es true?
and how do you calculate such a thing?

[gringer]

P-values are frequently (and in my opinion incorrectly) used to represent the size (or significance) of the genetic difference between two populations at a particular locus. It's better to use p-values as an initial filter, and rank based on another statistic that better represents the thing of biological importance (e.g. chi^2, odds ratio).

[nhaus]

okay.
I got another question in that context regarding the Odds Ratio(OR) and I will try to explain what I mean with an example:

There is a common SNP in Parkinson that is associated with a higher risk of getting Parkinson, e.g. G vs A.
The odds ratio of G is 1.5 . Does that mean that an individual is 1.5 times as likely to get Parkinson as an individual with the A allel?

[mastal]

See the wikipedia definition of Odds Ratio.

https://en.wikipedia.org/wiki/Odds_ratio