Making Sure to Change Only the Right DNA

If we are going to changeDNA in people, we need to make sure we only cause the changes we want. (NHGRI)

December 7, 2015

Water allergy aquagenic urticaria

-A curious adult from California

December 4, 2015

As strange and impossible as that seems, the answer is YES! Some people have an allergic reaction to water. This is called “aquagenic urticaria.”

These poor people often get red, swollen marks all over their bodies (except the palms of their hands and soles of their feet), and most also feel itchy. Some can even feel lightheaded, nauseous or have trouble breathing after touching it. Just from water!

But people have to shower, right?!  And wash their hands?! And what do these people do if they get caught in the rain?! 

About half of these people can deal with their symptoms by taking allergy medicines. These antihistamines are the same thing you can take if you are allergic to other things. 

But this only works for about half of people who are allergic to water. The other half can try something else – using UVB light to thicken their skin.

Does it run in families?

Sometimes more than one person in a family can be allergic to water.  This happens because the instructions that tell the immune system how to work are in our genes. And families share a lot of the same genes.

To understand all of this, let’s step back a bit and talk about cells.

Each of us is made up of trillions of cells.  We have different types of cells that do different things.  

Driving Genes Into the Wild

Giving these mosquitoes bad genes could save hundreds of thousands of lives each year. (Wikimedia Commons)

November 24, 2015

Gene editing to grow new limbs

-A curious adult from Lebanon

November 10, 2015

Not even the best scientists can agree on when (or if) we will be able to tweak our genes one day to grow new limbs. And changing things like the shape of our nose may be just as tricky! The exciting news though is that we now finally have the tools to at least make it possible.

Genes have the information that makes and runs a living thing. So to do the things you suggest we need to change or “edit” the genes.

Of Salamanders and Men

We humans start out as a ball of pluripotent stem cells in the womb, which end up forming all our organs. As these organs develop, however, all our pluripotent stem cells are used up to make different cell types.

So now I know what you’re thinking – how is it that we can still heal from some injuries? If you scrape your knee and lose some blood and skin, for example, your body makes new blood and skin cells to replace the ones that are lost. How does this happen without pluripotent stem cells?

Scientists can put these tools into cells by directly injecting them into the body. They can also take adult stem cells out of the body, edit the cells with these tools, and put the cells back into the body.  

Sounds a little bit like a science fiction novel, right? Actually, scientists have already done these operations in monkeys. They plan to test gene editing on people soon.

An Exciting Time

Sickle cell trait and anemia genetics

-A high school teacher from Texas

November 5, 2015

Each of their kids should have around a 1 in 4 chance for getting sickle cell anemia. They will also each have around 1 in 2 chance for having sickle cell trait and a 1 in 4 chance for not having either.

Your Genes Have The Instructions for You

So where did the glitch come from? Well, the instructions for making hemoglobin are found in something called DNA. Your DNA has the complete instructions for building, maintaining and running your entire body.

These instructions are found in stretches of DNA called genes. Each gene has the instructions for one small part of you.

The 1 in 4 Chance

In this case, both parents have sickle cell trait. That means they have one working and one sickle cell copy of the hemoglobin gene.

Now when they have kids, each parent will pass just one of their two copies down. This copy is chosen at random which means there are the following four possibilities:

Wolverine and Laura Kinney Genetic Differences

-A curious adult from the US

October 29, 2015

I would say Laura Kinney, or X-23, and Wolverine are somewhere between brother and sister and identical twins. But much, much closer to identical twins.  

They share almost all of their DNA. This is a lot more than the 50% that is typically shared between brothers and sisters.

But they can’t really be called identical twins, either. They still have some major differences.

There are parts of this that are inherited, but much of it is environmental. In fact, even identical twins with the exact same DNA differ in the way they use it. So, as a normally born child versus a clone, Wolverine and Laura may have many differences in how they use their DNA, even the parts that are identical.

So we’ve concluded that Laura and Wolverine are almost identical twins. All their chromosomes are exactly the same except her two X’s versus his X and Y. (And the relatively unimportant mtDNA.)

For example, if you know identical twins, you know they aren’t exactly the same. They each have their own special quirks.

Our DNA is the instruction manual to direct everything any of the cells in our body does. So why are identical twins different from each other?

It turns out that it is because they each use their genes a bit differently. Think about it like two identical cookbooks.

Silent Viruses Awaken Briefly in Early Human Embryos

Like zombies rising from their graves, "dead" viruses rise up from our DNA early in development. (Wikimedia Commons)

October 21, 2015

Blood type can be different from parents

- A curious adult from Alaska

October 15, 2015

No it doesn’t. Neither of your parents has to have the same blood type as you.

For example if one of your parents was AB+ and the other was O+, they could only have A and B kids. In other words, most likely none of their kids would share either parent’s blood type.

And that’s just one of many possibilities. There are lots of other possible combinations where two parents without blood type A can have a child with one. Here they are:

Two Copies of Each Gene, One from Each Parent

DNA is a set of instructions for making and running a living thing. So your DNA is the set of instructions for making and running you.

A lot of these instructions are found in long stretches of DNA called genes. Each gene has the instructions for one small part of you.

One of these genes goes by the name ABO. It comes in three flavors, or “alleles” —A, B, and O. Your blood type is determined by the combination of alleles of this gene you get from your parents.

Another Gene Determines Positive/Negative

So now I know what you’re thinking – you’re A positive, so what does the “positive” part mean?  It turns out there’s another important molecule on blood cells called the Rh protein.

You either have the Rh protein or you don’t. If you have it, you’re positive, and if you don’t, you’re negative. If you’re interested in knowing more about the Rh protein, you can visit one of our previous Ask a Geneticist answers.

Silent mutations can sometimes affect genes

-A curious adult from California

October 1, 2015

Silent mutations are DNA changes that don’t change a gene’s “meaning.” They are like trading the words shady and unscrupulous in a sentence. Both words are usually pretty interchangeable.

But not always of course. No one would say a tree is unscrupulous (unless it is an evil Ent of course).

The Meaning of Words (Codons)

As I said, a gene has the instructions for making a protein and a protein does a certain job in the cell. But what is a protein?

It is really just a bunch of molecules called amino acids strung together, one after the other in a certain order. There are around 20 of these amino acids.

Folded While You Wait

The key to understanding how silent mutations might affect a protein is realizing that the proteins are folded as they are made. So it starts to fold even before it is finished.

Parts of the protein that are supposed to fold together a certain way get folded before the next part comes out. Each of these separate folded parts are called domains. These domains then all fold on each other until you get a working protein.

Conjoined twins cannot have the same father

-A high school student from China

September 23, 2015

First off, yes, it is possible for twins to have different fathers. This goes by the exciting name heteropaternal superfecundation. It is much more common in other animals but it can and does happen in people too.

And of course twins can be conjoined. But these twins are identical which means by definition they have the same mom and dad. In fact, they have the same DNA!

Duncle or Mont

Imagine you go to a fertility clinic and your sperm and your wife’s eggs are combined and then the fertilized eggs are implanted into your wife. Nine months later she gives birth to a beautiful baby boy.

A routine blood test on the baby shows he is AB and a red flag goes up. There isn’t any easy way to explain how you and your wife produced the baby’s blood type since you are both A. The clinic must have implanted the wrong embryos!

Who’s Your Daddy?

As you tell, things can get pretty confusing pretty quickly. While there may be a natural tendency to identify one set of DNA as mine and the other as my twin, this isn’t really how it works.

A chimera is a wonderful mix of both twins. Neither is the true self even if the cells that first got tested happened to have a certain DNA. A chimera is really a fusion of two sets of DNA that make one unique person.

This also means that each child is equally related to the chimera. One child is not more or less related.