...

If the selected aligned data node was imported, reference assembly the data aligned to needs to be specified, choose the assembly the sequence is aligned to from the Assembly drop-down list within the MACS2 dialogue (Figure 1); if the alignment was performed in Partek Flow, this option will not appear.

...

The effective genome size is the genome size can be sequenced. Because of the  repetitive repetitive features on the chromosomes, the actual mappable genome size will be smaller than the original size, typically about 70%-90% of the genome size. There are presets of 4 species based on MACS2 recommendation¹ for this parameter:

...