The first Genesis was unisex. M5 and V5 (and all the other Generation 5 characters) were both morphs for Genesis. 

Genesis 2 took it back to separate male and female shapes to make different morphs and joints and such work better, and be easier on content artists. So V6 is a morph for G2F and M6 is a morph for G2M. 

There are utilities to transfer clothing and shapes between Genesis and G2M/G2F. 

If clothing is built for G2F then it will usually work on V6, but you might need to use DS's transfer utility on some things if they weren't made with the V6 morph built in, but it's pretty simple and only takes a few seconds. 

V6 has different UV maps than G2F. Each DAZ character for G2F has her own set of UV maps. If it's a 3rd party character that uses the G2F morphs sets then they will likely just use G2F's base UV maps. Unless the character requires V6 or one of the other official DAZ characters. (Olympia, Lilith, etc). 

The differences between Genesis, G2F/M, and earlier unimesh/millenium figures is the mesh and the rigging tech. They were all based on early versions of the same concept tho - one mesh to create multiple figures from. But the meshes themselves are different from one generation to the next, and Genesis and Genesis 2 don't work natively in Poser the way Generation 4 and previous versions did because of the rigging tech being native to DS. You have to use the DSON utility to import Genesis figures and their content into Poser.  

You can get legacy shapes for all the previous figures (at least back to Generation 3) to use the shapes and older content for the newest version of Genesis.

 

ETA: Unless you have some questions that are specific to Poser, I'm going to move this thread to the DS forum where you are likely to get more detailed info on Genesis.