Questions: How do genome-wide association studies (GWAS) help in understanding diseases? They identify differences in genetic markers between individuals. They focus on environmental factors causing diseases. They use genealogy to trace disease origins. They analyze protein sequences for disease diagnosis.

The answer is the first one: They identify differences in genetic markers between individuals.

Explanation for each option:

1. They identify differences in genetic markers between individuals.
   This is correct. Genome-wide association studies (GWAS) are used to scan the genomes of many individuals to find genetic variations associated with a particular disease. By identifying differences in genetic markers, researchers can pinpoint genetic factors that may contribute to the risk of developing a disease.

2. They focus on environmental factors causing diseases.
   This is incorrect. GWAS specifically looks at genetic variations and does not focus on environmental factors. While environmental factors are important in understanding diseases, they are not the primary focus of GWAS.

3. They use genealogy to trace disease origins.
   This is incorrect. GWAS does not use genealogy or family history to trace disease origins. Instead, it analyzes genetic data from a large population to find associations between genetic markers and diseases.

4. They analyze protein sequences for disease diagnosis.
   This is incorrect. GWAS does not analyze protein sequences. It focuses on genetic variations, such as single nucleotide polymorphisms (SNPs), across the genome to find associations with diseases.

In summary, GWAS helps in understanding diseases by identifying genetic differences between individuals that may be associated with disease risk.