Inheriting Kabuki syndrome

-A graduate student from the UK

February 7, 2017

Odds are that your husband isn’t a carrier for Kabuki syndrome because of how it is passed on. It tends to follow one of three patterns.

The most common way for people to end up with Kabuki syndrome is that it literally appears of out nowhere. Basically, the person’s DNA ends up with a new mistake in it that did not come from either parent. This kind of new mistake is called a de novo mutation. 

Most People Do Not Inherit Kabuki Syndrome

Kabuki syndrome is pretty rare. Only something like 1 in 32,000 newborns are born with it each year.

People with this condition can have a wide variety of symptoms in many parts of the body. They often have arched eyebrows or larger ears. Some will also have trouble with thinking and understanding, so special education can be helpful.  Click here to learn more about the symptoms associated with this condition.

Autosomal Dominant Kabuki syndrome

Mutations in the KMT2D gene cause around 75% of Kabuki syndrome cases that have symptoms. So this is the most common cause.

Like the majority of our genes, most everyone has two copies of KMT2D. We get one copy from mom and one copy from dad.

There only needs to be a problem or mutation in one copy of the KMT2D gene to cause Kabuki syndrome. This is called autosomal dominant inheritance.

Ethnicity DNA Percentages Not Solid

-A curious adult from Florida

January 31, 2017

If the 51% were a rock solid number then yes, both parents would have to have some Italian in their DNA. After all, you only get 50% of your DNA from one parent! At least 1% of your Italian heritage would have had to come from the other parent.

But in the real world of DNA ancestry testing, that percentage is a bit more wishy washy. I think of them as telling you that a sizeable part of your heritage looks Italian in the DNA test. Could be lower, could be higher.  

Parent and Child with 40% Italian

To understand how a parent whose DNA looks to be 40% Italian might have a child with the same percentage, we need to take a step back and review how DNA is stored in our cells. And how it is passed on.

DNA is stored in something called chromosomes. People usually have 46 of these.

These chromosomes come in nearly identical pairs. One from each pair comes from mom and one from dad.

Imagine these are the 23 pairs:

Ancestry.com

Ancestry.com has a very useful resource that gives you the likely range of your percent ancestry. In other words, it lets you know how reliable that 51% is and what its upper and lower limits are.

Let’s use my results as an example. If I click on a particular ancestry, the following image comes up:

This is a little hard to see so I will break it up into two separate images:

Third and fifth cousins DNA tests

-A curious adult from British Columbia

January 17, 2017

DNA can show they are related. You probably need a family tree to figure out the exact relationships. (Wikimedia Commons)

The table also gives you some idea about how many first, second and so on cousins you might expect to have. This is based on around 2-3 kids per generation and so doesn’t fit everyone’s situation but it does give you an idea about how the numbers increase. You probably have more than 100,000 seventh cousins for example.

What these tests are less precise about is the actual relationship. So sometimes the test will call someone as a third cousin when they may actually be a fifth cousin and so on. The more distant the relationship, the less precise the relationship assignment.

Let’s take an example where you’d think the test could pretty easily tell two people apart—first and second cousins.

Remember, first cousins should share 12.5% of their DNA while second cousins should share 3.125%. You can see these numbers in red in the table (1C is first cousin, 2C is second cousin).

In terms of cM, first cousins share, on average, 881 cM, while second cousins share 246 cM. These numbers are in the same ballpark as the percentages—first cousins share around four times as much DNA.

Somatic mutation mosaic

-A curious adult from Missouri

January 10, 2017

No it doesn’t. A change (or mutation) in the DNA of a muscle cell can’t be transferred to another muscle cell. Each cell has its own set of DNA.

The only way a mutation like this can spread (at least in people) is if it happens in a cell that makes copies of itself. Or if the mutation turns the cell into one that makes copies of itself.

Otherwise that lonely muscle cell in your finger will have a mutation that the rest of the cells in your body do not.

Early Mutations Can Spread

When a human being is first made, it is just a single cell! This single cell eventually divides over and over to become an adult with trillions of cells. These early cells are called stem cells.

During the early parts of human development, stem cells are very important. This is because just one of these stem cells will end up being many different kinds of cells in an adult.

Bacterial Sex Swaps DNA

Large organisms like humans are made out of many kinds of cells. Like cogs in a machine, all of those cells have to work consistently the way they were designed.

Humans also have DNA wound up in complicated structures called chromosomes for organization. It would be hard for the cells in our bodies to change up their DNA.

Smaller organisms that are just one single cell, like bacteria, often share and exchange DNA. This is easy for them because they can organize their DNA in little rings called plasmids.

Identifying incest with DNA

-A curious adult from Michigan

January 4, 2017

That’s an interesting question! It may actually be possible to get some idea about how related your parents are.

But you probably won’t able to say conclusively. The only way to know for sure would be to test the parents or another relative.

One way you can use your DNA to see if your parents might have been related is through a program like GEDmatch’s “Are your parents related?” app. 

DNA Mixes Between Generations

To understand how we can test someone’s DNA to check if their parents were closely related, we need to know a little more about how DNA works.

DNA has the instructions for making us. Since we all look a little bit different, it’s not surprising that our DNA is different, too.

Some people are tall and others are short, some have blue eyes and some have green or brown. These differences are coded in our DNA.

As you can see, only the child with related parents has any significant amount of this DNA. The child with the unrelated parents has none of these runs of homozygosity. This is because the chromosomes of the child with closely related parents are very similar to begin with.

Scientists can check for these regions in a person’s DNA, and count how many there are. Children born to unrelated parents will have relatively few of these areas.

DNA damage mutation usually harmless

-An undergraduate from France

December 13, 2016

The short answer is that UV rays can damage any part of our DNA. So we could get a mutation in a gene that could affect muscle movement.

Luckily for us, UV rays can only damage the DNA in cells they can reach: our skin cells. Our skin cells don’t actually use the muscle gene (see below), so a mutation in it wouldn’t matter for them. The gene in all of our muscle cells would still be fine.

1) Most of Our DNA Isn’t Instructions

DNA is like an instruction book for making a living thing. The most important parts of it are the genes. Each gene is like a specific instruction.

We can think of our DNA as a giant cookbook of recipes to make you. Each recipe is like a gene and tells us to do something important.

The most important mutations are usually the ones that happen in a gene. These can sometimes cause the gene to not work or work differently than usual.

DNA Changes and Skin Cancer

So our bodies have lots of layers of protection from mutations caused by UV rays.  But nothing is 100%. Sometimes those 2 eggs become 12 eggs in the recipe and our pancakes are ruined.

Luckily, only a very small percent of genetic changes from UV rays actually cause problems. Remember, for a mutation to cause damage, it needs to happen inside a gene, not get fixed, and cause a problem with a gene that that cell uses.

Parent children different blood type

-A curious adult from Michigan

December 6, 2016

While a child could have the same blood type as one of his/her parents, it doesn’t always happen that way. For example, parents with AB and O blood types can either have children with blood type A or blood type B. These two types are definitely different than parents’ blood types! 

But two O parents, for example, will pretty much always have O kids. They will match both parents.

Each specific instruction for a small part of you is called a gene. As humans, we all have the same 20,000 or so genes. What makes us different are the different versions of these genes.

For example, we all have the blood type gene, ABO. What gives us different blood types is that this gene comes in three different versions: A, B, and O. 

In a simple world, the three versions would give three blood types and a child would have one of the blood types of the parents. But we don’t live in a simple world, now, do we?

Gene-Protein Relationship

I told you there are all these different genes and that they come in versions. But what exactly do they do and what is different about them?

Genes are the instructions for proteins. And different gene versions make different versions of a protein. 

So the A version of the ABO genes makes the “A” version of a protein, the B version a B version of a protein and importantly, for our discussion, the O version doesn’t make either.

Why ancestry and relatedness look different in DNA

-A curious adult from New York

November 18, 2016

You’re absolutely right! Since you and your siblings are not identical twins, you almost certainly don’t have the same exact DNA.

DNA tests like Ancestry.com, though, only look at some of your DNA to determine your ancestry. And they look at the parts of your DNA that are more likely to be the same between people from the same parts of the world.

Picture your DNA as a long book. In the old days before computers and modern technology, books were copied by hand. Monks in monasteries carefully transcribed new copies of books, but sometimes they made mistakes.

Imagine that a monk in a monastery in Poland is copying a book and makes a mistake. They then lose the original and use the copied book to make new copies. Now all the copies of that book in the Polish monastery will have that new mistake.

A Mix of Mother and Father

Imagine our monk in Poland who copied his book with a couple of mistakes. Let’s say a bunch of monks from this monastery take a copy of the book and found new monasteries across Poland.

When they get to their new homes, they start diligently copying their manuscripts. And they each make their own monastery-specific mistakes. Now every book in Poland is no longer the same.

Balanced translocation combination kids children

-A curious adult from Florida

November 15, 2016

Great question! Your friend’s doctor is right that there are four combinations for her kids.

This is important to know because two of the combinations might cause problems for the pregnancy and/or the child, and two won’t.

There are three different ways her kids could get a translocation too. There is also one way her kids won’t end up with one.

However, if we delete one S, we change the meaning of the word! Now we’re not talking about a scoop of ice cream or a piece of cake anymore. Instead we’re talking about a place where it hardly ever rains. 

What happens when we add an extra S? We end up with something meaningless. 

There are Four Combinations of Chr1 and Chr2

Now we know what a balanced translocation is and how parents pass on their chromosomes to their children. We have all the information we need to figure out the four combinations the child in question can inherit.

Let’s say a parent has the balanced translocation I showed earlier:

Genetics scoliosis

-A curious adult from Idaho

November 8, 2016

Great question, the answer seems to be yes!  We know that the type of scoliosis you’re asking about is at least partly hereditary. 

There’s much more to the story, though.  As you can probably tell from that sentence, the sideways curvature of the spine that is scoliosis is not that simple to figure out.

Of course this doesn’t tell us if scoliosis is genetic at all. Twins usually develop and grow in the same environment. To see if scoliosis is genetic, we compare the results to fraternal twins. 

Fraternal twins only share about half of their DNA, just like any other siblings.  So if two twins in a fraternal pair and two twins in an identical twin pair have the same percentages, then we know that scoliosis is purely environmental.  But researchers didn’t find this.

Scientists first take a bunch of different people with and without a genetic condition.  Then they look at their genetic make-up.  Then they compare the genetic differences in the people with the condition to the people without the condition. 

Let’s say, everyone in the group with the condition has a certain genetic change.  But no one in the group without the condition has that change. If we have enough people in the study, then we can say that change is important and probably causes the condition.

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