Question: Hi Paul, I would like to ask this: would there be a possibility to biologically engineer an extinct species, if there were egg and sperm cells found frozen in ice, would it be possible to use another ancestor as the host?

Paul McKeegan answered on 13 Nov 2017:

Hi! I see you are a fellow Jurassic Park fan. There is a possibility of bringing some species back, but there is a limit based on how long ago they went extinct. Sadly, I don’t think we will ever see a real dinosaur though 🙁
There are scientists trying very hard to bring the wooly mammoth back though!
It is highly unlikely we will ever find usable eggs or sperm frozen in the ice as these cells are incredibly fragile and it takes a lot of effort, after years of research, to freeze them in the lab. We are pretty good at this now though and ‘cryopreservation’ of sperm, eggs and embryos this way has enormously improved fertility treatment.
In terms of bringing species back, we would need the complete intact DNA genome and a suitable ‘host’. There are scientists who extract DNA from fossils to find out about extinct species. The DNA is almost always fragmented and damaged, but sometimes there is an intact sample. You would then need to put the extinct animal DNA into the host animal’s egg. This actually worked, briefly, with a species of Spanish goat – the scientists removed egg cells from the last animal of the bucardo species as soon as it died, then tried this process with other goats as the surrogate mother. One calf was born, but died within hours due to a lung problem.
There is a team of scientists who are gradually replacing elephant genes with woolly mammoth genes. This would not quite bring the mammoth back, but create a mammoth-like elephant subspecies. They have changed 45 genes so far, and have another 1645 to go!