GWAS
A GWAS tests individual genetic variants (usually SNPs) across the entire genome to determine whether any are statistically associated with a phenotype or disease (e.g., comparing allele frequencies between cases and controls).
GAS
A GAS tests associations at the gene level by combining the effects of multiple SNPs within a gene. Unlike GWAS, which tests individual variants, GAS determines whether a whole gene is associated with the phenotype.
How are gene association studies different from linkage studies that
find disease-associated genes
- Gene association studies are NOT pedigree based
- Genetic association studies examine very large numbers of unrelated people (case vs. controls groups)
- Diseases examined are complex diseases where many interacting genes are responsible for the phenotype
What is a GWAS
- It is genome wide association study
- It does not depend on traditional pedigree analysis
- It looks for an association between a genotype
and a phenotype (can be a disease) - 1 000’s of individuals make up a study group
which is compared to a another (control) group - 100 000’s to 1 000 000’s DNA variants (or SNPs)
are examined
SNPs
SNP (pronounced snip) is a Single Nucleotide Polymorphism
* These are locations within genome of nucleotide substitution
* At least 1% of a population must have alternative nucleotide variant to be considered a SNP
* The most common type of genetic variation among human genomes
> 18 million human SNPs have been identified
SSR
Highly polymorphic due to SSRs mutating easily because DNA polymerase can slip during replication
Huntington’s disease is an example of an SSR occuring in inside a gene and causing disease
