You could inbreed leopard geckos. Based on what I have read don't quote me on this you just need to introduce new genes every 5th generation. Depending on who you ask you will get a different answer as far as weight but 50 grams is enough.

You measure the weight using a scale. I use a digital scale you can get one online or they sell postal scales which is the samething at Office Depot, Office Max, etc. As babies it's ok to house a male/female or female/female just don't house two males together. Just a suggestion you should check out if there any reptile shows in your area and buy them off a reputable breeding instead of Petco. I'm not anti-Petco or anything I've bought geckos there before it's just a suggestion. Hope my post helped. Good Luck with your purchase!