Problem:

Question: When performing a GWAS, which of the following would increase your chance of detecting a significant association between a disease phenotype and markers linked to the causal gene(s)?

a. The allele responsible for the disease arose from a mutation that occurred only once in the population and then increased to higher frequency by genetic drift.

b. The alleles responsible for the disease are tightly linked to some of molecular markers used in the study.

c. The disease is caused by many genes each of small effect.

d. Both a and b

e. All of the above

Give reasoning with your answer.