Other Fun Stuff

Can human DNA be "spliced"with animal DNA while in the womb creating a literal chimera, like a half man, half beast? If this is possible do you think it will ever become as common in the general public as tatoos?

-An elementary school student from Florida

March 29, 2005

What a fun question! Doesn't seem likely to me that it will be happening anytime soon but, who knows?

Let's look at something like a centaur -- the half horse, half human from Greek mythology (and, of late, Harry Potter).

A centaur has the body, arms, and head of a human and the legs, body, and tail of a horse. We need to have the top of this creation develop as a human and the bottom as a horse.

To pull something like this off, we would need to replace the human leg development genes with horse body, legs and tail development genes. Or we could replace a horse head's genes with those needed for a human body, arms, and head. This would not be easy...

First off, there are lots of genes involved in making a leg. We would need to replace most if not all of the human ones with horse ones to get horse legs on a human. Ditto for the body and the tail.

This would be more doable if all of these genes were in some single convenient place. For example, all leg genes on chromosome 1, eye genes on 2, arm genes on 3, etc. Unfortunately, it doesn't work that way.

The various genes are scattered around all 23 of our chromosomes. This means we can't do something "easy" like replace a horse chromosome with a human chromosome. (This still would be incredibly hard, by the way.)

What we would need to do is replace lots of individual genes to try to make the centaur. This is way beyond what we can do now -- it is hard enough to add back a gene let alone replace one. And none of this even gets into another area, regulation.

Development genes need to be on at the right place for the right amount of time. If they turn on in the wrong place, you might get eyes in funny places (as happened with a fruit fly, see below). If they come on at the wrong time, you can have problems like, for example, cancer.

Now every living thing controls when and where to turn on its genes differently. Genes, of course, are an important part of this process.

These controller genes would also need to be moved to the new animal but they couldn't mess up the other animal's genes that were already there. Most likely, you'd get a mess instead of a centaur.

Let's think about something easier -- like making a human with a tail. From what I've read, we have old, broken tail genes in our DNA. With less trouble than making a centaur, maybe we could get these tail genes working again.

So, would tails become some sort of fashion statement like tattoos? Hard to say but one fact may make it unlikely.

As you recognized in your question, these kinds of changes would probably have to be done to someone before they were born. So, some parents without tails would have to decide they'd like to have a kid with a tail. Possible, but unlikely I'd think.

Anyway, great question. It really points out how hard it is to make these sorts of changes all at once. No wonder it takes biology millions and millions of years to create new species.

By Dr. Barry Starr, Stanford University