Genuine Glofish can be seen at the following link. They have a jellyfish gene added to them and are naturally coloured due to the gene.
https://www.glofish.com/meet-glofish/glofish-gallery/
If they have a coloured line on their body, then they are either painted or injected. Most places use paint and have a kid with a paint brush painting lines on the fish. The paint eventually wears off and you end up with a normal skirt tetra that is either a black or white version.
Either way if they have produced fertile eggs, the eggs will hatch and you will have baby tetras. The eggs are sensitive to light and should be kept in the dark. The babies are small when they hatch and you normally use infusoria or green water to feed them during the first few weeks. You can also buy "Fry Food for Egg Layers" from pet shops, or use a boiled egg.
You hard boil an egg and remove the shell and white bit. Push the yellow yolk through a handkerchief, into a small container of dechlorinated water. Put a lid on the container and shake it up. Then use an eye dropper to suck some of the solution out and add it to the fry tank. Do this several times a day and after a week or so you can start adding newly hatched brineshrimp. You can buy brineshrimp eggs from pet shops or online.
There is more information about egg yolk, brineshrimp eggs and feeding baby fish at the following link.
http://www.fishforums.net/threads/back-to-basics-when-breeding-fish.448304/