Final answer:
GWAS can scan the whole genome to find QTLs by testing for marker variants and doesn't need controlled crosses. It helps find SNPs linked to diseases like Crohn's but doesn't establish causation or identify a single responsible gene.
Therefore, the correct answer is: option "GWAS can scan the entire genome for QTLs by statistically testing for marker variants".
Step-by-step explanation:
Genome-Wide Association Studies (GWAS) are a method that examines the entire genome to identify single nucleotide polymorphisms (SNPs) associated with diseases.
The true statement among the provided options is that GWAS can scan the entire genome for QTLs by statistically testing for marker variants.
GWAS does not require controlled crosses or the formation of introgression lines, rather it compares large groups of individuals to find genetic variants that influence disease risk.
Conversely, QTL mapping can analyze organisms in random mating populations and is not typically used to directly identify the gene responsible for a trait but instead locates regions of the genome that are linked to phenotypic variation.
For example, several genes associated with Crohn's disease have been identified using GWAS, providing insight into potential pathways and mechanisms involved in the disease.
However, it's important to note that GWAS identifies associations and does not determine causation or single out one gene that plays the sole role in disease development.