There are two approaches/ways of creating sequence objects in mx.
Sequences "without" specimen vouchers
If you do not have a PCR_id or extract to which to tie your data then you must include a OTU and gene. You may NOT also include a PCR at this point.
Sequences with specimen vouchers
If you have followed the specimen->extract->pcr path then you need only include the pcr and the sequence to create a valid record. If you select a PCR you may NOT include gene or OTU data as these are derived automatically.