Hello everyone! Usually, there are two lines drawn at the manhattan plot: suggestive and genome-wide significance lines. It is clear that the genome-wide significance line corresponds to Bonferonni-corrected p-value namely 0.05 divided by the number of SNPs tested. The suggestive line lies a little bit lower than genome-wide significance lines and serves as a more soft threshold. The googling on how the suggestive line is calculated led me to no success. If you know paper explaining it or a FAQ/tutorial please recommend.

Thank you! If I understood you correctly it is just a matter of convention without statistical justification.