You have a very simplistic view of genes, just like creationist I once argued with who had a simplistic view of why fossils are ordered the way that they are... "because the more advanced animals run faster and therefore got to the top sooner!"
If the genes are very similar or the same, the biological process associated with this gene is very similar or the same.
Incorrect. We carry the same genes for growing a tail, but most all expressions of these genes result in harmful deformities.
If the genes are not the same, the biological processes are not the same. Also incorrect.
Read up on convergent evolution.
Your theory that "similar genes = similar functions, therefore, similar organisms = similar DNA" falls flat on its face, period. Anything built by endless generations of improvisements will look radically different than anything built from the ground up. Our genetic history, with endless leftovers that used to encode for one specific function and now not serving any known purpose whatsoever, looks far more like the former than the latter.
If similar genes do not mean similar function, then common descent truly is meaningless. Especially in light of your 'convergent evolution' claim.
If 'convergent evolution' is true, then 'evolution' can produce similar genes without 'common descent' and 'common descent' has been falsified.