Upside down leaf growth?

Does look strange, possible genetic eff up, but I have seen seedlings like this return to normal growth once they become a little more established. Personally I would pull seedlings like this out as it is not a good start to life, however, as I said they can resume normal growth. If you are super keen on this seedling, give it until 2 more sets of leaves have grown and if these next 2 sets are still weird, pull it out, as it will only grow more slowly than the rest of your seedlings and will no doubt produce weird mutant flowers too. If the leaves do revert back to normal growth, just think of this seedling as your "special" plant that just needed to work things out properly before getting going! Hope this helps.... Organoman.