Would it be a good idea if every country measured longitude from its own prime meridian?

The answer is - No.

There's a reason why the prime meridian Greenwich is used worldwide as a starting point for measuring longitude, and that is so that confusions and different values for the same longitude are avoided, and that it is universal for all the world for measuring longitude and everyone can simple understand each other. But if every country started to measure the longitude from its own prime meridian, than we will have a situation where all countries will have different values for the same places around the world, and that will complicate things big time, and make it hard for collaboration and understanding.

"do a testcross with a homozygous recessive plant."