Sisters not in same ancestry genetic community

-A curious adult from Georgia

August 24, 2017

No it does not. In fact, it is not uncommon for two siblings to be in separate genetic communities.

At first this might seem weird given that two sisters are about as closely related as any two people can be—50% or so on average. How can they not be in the same genetic community?

There are a couple of reasons.

A 50-50 Chance

First off let’s talk about how only one sister can get the bit of DNA that links her to a genetic community.

To do this we will imagine that mom is a member of this genetic community. She has a bit of DNA that is linked to the genetic community.

Let’s represent mom’s DNA like this:

A little explanation is in order.

From Chromosome to Sliver

Next let’s figure out where that little bit of blue at the end of the chromosome came from. As you’ll see, it came from an all blue chromosome from that genetic community.

Let’s say this is the original ancestor you are tracing your genetic community back to:

Note all of the chromosomes are blue. Now let’s have her have children with someone outside of the community:

AB and O blood type parents having A and B children

-A curious adult from California

August 16, 2017

Believe it or not, in this case having a blood type different from either parent is by far the most common result. In most cases, an O parent and an AB parent will have only A or B kids.

It is only very rarely that they might have an AB or an O child (see the links at the end for these exceptions). Isn’t genetics fun!

Three versions

As humans, we all have the same basic set of genes. What makes you different from me is that we have different versions of some of our genes.

So there isn’t a blue and a brown eye gene for example. Instead there is a gene that comes in a brown and a blue version. (Well, that is a simplification. It actually comes in a brown and a not-brown version.)

The ABO gene comes in three versions: A, B, and O.

Four Blood Types

One Shall Pass

From the previous section we can see that you have an A and a B and that your partner has two O’s. Maybe something like this:

(Adapted from Pixabay image)

(I made the mom AB and the dad OO here but it works the other way too.)

CRISPR human embryo

-A curious adult from California

August 8, 2017

It is a big deal but probably not as big as some media outlets would have you believe (or believe themselves).

It is big because this is the first time that scientists have used the gene editing tool CRISPR/Cas9 to specifically change a gene in a human embryo here in the US. This is a very big step.

Gene Editing in an Embryo

In the past, the CRISPR gene editing system has needed three things to edit a gene:

Two Copies: More than Twice as Hard?

We have two copies of most of our genes. We get one from mom and one from dad.

In this study, they worked on a disease where only one of the copies needs to be damaged to cause a disease. This is called a “dominant” genetic disease.

In this case, Cas9 cut the damaged copy but left the working one alone. The embryo the used its second working copy to fix its broken gene. It ignored the DNA the scientists added.

DNA shared by siblings

-A curious adult from the U.S.

August 2, 2017

In this case you are almost certainly full siblings. Because of how this (and many other companies) calculate shared DNA, that 38% number is actually equivalent to 50%. In other words, the two of you do share around 50% of your DNA.

The reason they report 38% has to do with how they figure out shared DNA. And how DNA is passed from parent to child.

The first thing to notice is that each parent has two rectangles. This is because all of us essentially have two copies of our DNA. Each copy is a bit different which is why one rectangle is a solid color and the other has stripes. (And also a big reason why we aren’t all exactly alike!)

When we have kids, we pass down one rectangle’s worth of DNA. That is how generation after generation people keep two copies of their DNA—they get a complete copy or rectangle from each parent.

Let’s see what these parents’ first kid might look like:

So for example, they share a chunk of mom’s blue striped DNA (the first box in the middle on the left) and a chunk of mom’s solid DNA (in the bottom box). Notice also that in some areas, like the top of the blue rectangles, they do not share DNA.

If we tally this up, we will probably get around 50% shared DNA. Here it might be a bit more or less than that but keep in mind that this is just an example. Real life is more complicated.

Genetics of skin color

-A curious adult from North Carolina

July 25, 2017

The short answer is, yes! A couple can have a baby with a skin color that isn’t between their own. The long answer, though, is much more interesting.

The long answer has to do with the parts of your DNA that give specific instructions for one small part of you. In other words, your genes.

As you can see, if you have two babies, they might end up with very different decks! And so very different skin colors.

This random dealing actually happens. Some mixed race parents have twins that look very different (click herehere and here for some great pictures of real-life examples).  

It turns out this switch doesn’t just change skin color. Hair color is also affected!

The rest of the person’s genes are saying, “make the hair colored!” so the person isn’t going to be blonde. But the person can’t flick the switch for brown, so their hair turns out red!

Genes Are Important, But You Still Have Control.

Your DNA contains all the information to make you. But that doesn’t mean it controls all of your future!

Curing sickle cell anemia

-A middle school student from New Hampshire

July 18, 2017

Not very easily! Right now a cure involves a bone marrow transplant and these things are pretty dangerous.

According to this site, 5-10% of young sickle cell patients don’t survive the transplant. The numbers are so bad for older people that it isn’t usually even offered to them.

Some new research suggests that there may be a way around this last problem. In this new approach they fix a patient’s bone marrow cells and put them back in the patient. The cells match because they are the patient’s own cells.

Back in March, 2017, a group of scientists reported that this new approach seems to have worked for a teenager with sickle cell. We will have to wait and see if this can become a new way to cure lots of people of their sickle cell.

Fixing the Typo in Sickle Cell

Fixing the typo in sickle cell is a tricky process, although it can be done. To make the process easier, scientists just add a copy of the correct instructions. They add a copy of the gene that does not lead to sickle cell.

Scientists use viruses to add a copy of the gene with the right instructions. These viruses naturally insert DNA into human cells and so are the perfect tools for this “gene therapy.” 

Resurrecting Neanderthals

-A curious adult from Texas

July 7, 2017

Just barely. It would take a lot of work and take a long time but if we wanted to, we could just about recreate a Neanderthal.

Since we know what Neanderthal DNA looked like, you might think it shouldn’t be too hard to resurrect one. After all, knowing Neanderthal DNA means we have all the instructions for making a Neanderthal.

Inserting Lab-Made DNA into a Cell

Another way to get Neanderthal DNA into a cell that might be possible in the near future is to make the DNA in a lab and get a cell to take it up. Scientists have been able to do this with very simple beasts like bacteria but anything much more complicated is much trickier.

Here the tricky part would be growing one of these iPS cells all the way to a baby Neanderthal. No one has yet done this with people but it should be possible. Scientists have been able to do something similar with mice for years.

Scientists coax the mouse iPS cell into an embryo and then put that embryo into a surrogate mouse. The embryo grows and develops in the womb and in the end you have a mouse pup.  

Odds for a child with sickle cell trait

-An undergraduate from Nigeria

June 28, 2017

To quickly answer your question, your third child still has a chance to end up with sickle cell trait. In fact, assuming your husband is not a carrier, your next child has the same 50% chance your other two kids did.

Think of it like flipping a coin. When you flip a coin, there is a 50% chance that you will get heads and a 50% chance that you will get tails. Do the chances change with each flip? Nope. 

The gene involved in sickle cell trait is found on chromosome number 11. It is called HBB and makes hemoglobin, the part of our blood that carries oxygen.

The HBB gene can come in at least two versions (or alleles): HbA and HbS. The HbA allele causes no problems but the HbS version can lead to either sickle cell trait or to the more severe sickle cell disease.

This means that each child has a 50% chance for having sickle cell trait. What it doesn’t mean is that half your kids will have sickle cell trait and half won’t.

This is a point that is often confusing about Punnett Squares—they do NOT mean that if you have four kids, two will have sickle cell trait and two will not. It is only figuring out the odds for each child. Like figuring out the chances for heads or tails in a coin flip.

Fragile X premutation

-A curious adult from India

June 22, 2017

Fragile X is a tricky genetic disease. Given that you don’t have the disease you are either not a carrier or a sort of carrier.

In the first case your kids aren’t at any risk for getting Fragile X. You are not a carrier and so you can’t pass it on to them.

In the second case your daughters are at a very, very, very low risk of having Fragile X (your sons are at no risk). However, in this second case, your daughter’s sons have a higher risk of getting Fragile X.

This isn’t just important for gender because the cause of Fragile X is on the X chromosome (that is where the “X” comes from). Your brother has Fragile X, which means it came from your mom because he got a Y from dad. Mom is a carrier which means she has the chromosome that can lead to the disease but does not have the disease because of her other X.

Now we know your mom is carrier, but we don’t know what kind of carrier she is. There are two kinds of carriers with Fragile X—premutation and full.

Your Daughters’ Children

If a daughter ends up with the full blown mutation, then each of her sons has a 50% chance for ending up with Fragile X. (Each daughter has a 50% chance too but remember that if they have any symptoms, they would be less severe.)

It gets a little trickier if a daughter has a premutation because now there is a higher chance it can transform into a form that can cause Fragile X. Not 100% but significant. (We can’t give exact numbers because it depends on the specific premutation a person has.)

Identical twin great aunt grandmother DNA

-A curious adult from Vermont

May 31, 2017

Yes it would. At the DNA level, you are related to the baby more like your identical twin sister is. You are actually closer to being the child’s grandmother instead of his/her great aunt.

This is because you and your identical twin sister essentially share 100% of your DNA. So when you look at her kids and their kids it is like looking at your kids and your grandkids. Well, only at the DNA level.

So dad has a dark blue and a light blue chromosome and mom has a dark orange and a light orange one. Here dad passed his dark blue one and mom passed her dark orange one.

This child got half his/her DNA from dad (dark blue) and half from mom (dark orange).

But this turns out to be much too simple! Chromosomes are rarely inherited whole. 

Before getting packaged into the sperm or egg, the two chromosomes in a pair swap DNA.  You end up inheriting a chromosome that is a mix of the two from your parent. 

Exploring Your Case

Let’s apply our new knowledge to your case. Here is a summary of what we learned about how much DNA is shared in different family relationships:

Now let’s take a look at your family tree and fill in some of the relationships: