Daughter vs niece paternity test

-A curious adult from Australia

November 12, 2016

The testing company is right. For reasons we talk about here, a standard paternity test will have trouble telling two potential fathers apart if they are brothers.

Test Results

This is what the result might look like from 23andMe if she were his daughter: 

And here is what they would like if she is his niece: 

A pretty big difference. With the daughter, everything is shaded in light blue but with the niece, only some of it is.

Where All That Blue Comes From

If you know a bit about DNA, these results might be a bit confusing. We get half our DNA from our moms and half from our dads. So why does the daughter seemingly share 100% of her DNA with her dad?

She doesn’t. It kind of looks like that because of how the data is reported here.

Remember, we have two copies of each of our chromosomes. We get one from each pair from mom and one from dad.

Best half sibling DNA test

-A curious adult from Mexico

January 7, 2016

Many of the DNA tests you might come across on the internet for showing this kind of relationship wouldn’t be very useful. Most of them are too weak to see such a distant relationship.

In fact, these tests might not even see it with one of the parents included. They have a better chance but it is still an odds game. They can only say how likely it is that two people share a single parent.

Few vs. Many

Most people’s DNA is split into 23 pairs of chromosomes. Each chromosome is one long piece of DNA.

In total, there are over 6 billion individual parts of the DNA that can be looked at. The individual parts are the famous A’s, G’s, C’s and T’s you may have heard about.

A standard test looks at a spot here and a spot there. It sees how many of these markers (as these spots are called) two people have in common and figures out relatedness that way.

Your Results

Each company will report back on how much DNA the two of you share and give some possible relationships.

Half siblings share 25% of their DNA but so do an uncle and a nephew or a grandparent and grandchild. The companies will make a reasonable guess based on the data but they can get it wrong.

For example, when my half-sister and I did a 23andMe test, the result came back that we were grandfather and granddaughter. A bit mortifying but understandable given the 30 or so years between us.

Color blind less severe inheritance

-A curious adult from Minnesota

December 16, 2015

Given your parents, you were most likely either going to get your dad’s colorblindness or not be colorblind at all. And it is for the reasons you talk about.

How bad a case of colorblindness you get is often inherited. And in women, you end up with the less severe form of colorblindness that each parent happens to pass to you.

Your dad will pass his colorblindness to you each and every time. But your mom will either pass her severe form or none at all.

This matters here because colorblindness is associated with the X chromosome. And if you have two X’s, the best one for color vision wins out.

This is why men are colorblind more often than women. They have just one X and if it says to be colorblind, they will be colorblind.

The story is very different for women. Because of their two X’s, they are much less likely to be colorblind.

If they have an X that doesn’t lead to colorblindness, it doesn’t matter what the other X says. She won’t be colorblind.

Mild or No Colorblindness

OK so let’s break down your case.

Your mom is not colorblind but one of the more severe forms does run in her family. This means she either has two perfectly fine X’s (in terms of colorblindness) or one of her X’s could lead to colorblindness.

In the second case she would be called a carrier. She can pass on colorblindness but does not have it herself.

Your dad has a mild colorblindness which means his X has it too. And this is his only X.

Advantages of psoriasis

-A curious adult from Germany

December 9, 2015

We don’t know a lot about how psoriasis started or why it is still as common as it is. In fact, we don’t even have a good handle on what causes it!

What we do know is that it is a condition where people have patches of skin that are discolored or a different texture from the rest of their skin. We also know that it happens because their immune system attacks their skin by mistake. And importantly for the discussion here, we know that it is genetic.

One idea is that a lot of the genes that we find in people with psoriasis are helpful in fighting HIV. Genes that protect people from getting AIDS are obviously an advantage. But it’s important that we keep two things in mind.

Sickle cell anemia and malaria

Sickle cell anemia is a genetic disease that makes people very sick. This means that they may not be able to have children, and we would expect sickle cell disease to disappear.

But sickle cell anemia is much more common than we expect. Why is that?

It turns out that having mild sickle cell disease (called sickle cell trait) protects people from malaria. This disease has been infecting humans for almost 5,000 years and for most of that time has been incredibly deadly.

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.

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