komodo dragon parthenogenesis not clone

-A curious adult from California

June 7, 2016

If humans had babies like Komodo dragons sometimes do, there'd be no need for sperm banks. Well, not unless mom wanted a little extra genetic variety from dad.  

Normally, babies get half their DNA from mom and the other half from dad. But this isn’t always the case in nature.

When 2 x ½ is Not the Same as 1

To see why this is, let’s imagine that a woman had babies by doubling the DNA in her egg like a Komodo dragon sometimes does. And that she has AB blood type.

Turns out that none of her kids would be AB like her—they’d all be A or B. Let’s see how this works.

Scattered throughout your DNA are the genes that make up the instructions for making you. Each gene has the instructions for one small part of you.

A Virgin Birth Gives Males (For Komodo Dragons)

For most animals, whether you are genetically a boy or a girl is determined by which sex chromosomes you have.

In people this is decided by the X and the Y chromosome. Genetic males have an X and a Y and genetic females have two X’s.

This is why in people, dad determines the sex of the baby. Mom can only give an X, but dad can give an X or a Y.  If baby gets X from mom and X from dad, then genetically the baby is a girl.  If baby gets X from mom and Y from dad, then the baby is a boy.

Pectus Carinatum genetics

-A graduate student from Belgium

May 31, 2016

Pectus carinatum (PC), as you probably know, is when someone has a difference in the way his or her chest wall is formed. It often looks like the chest sticks out father than is typical.

How Does Pectus Carinatum Run In Families?

There are different ways that PC can be passed on.

If someone has a genetic condition like Marfan syndrome, then we know exactly how it gets passed down. In this case, if one parent has Marfan syndrome, then each child has a 50% chance of having it too.

Scientists have even been able to figure out which gene is involved. People with Marfan syndrome often have mutations in a gene called FBN1.

So What’re The Chances My Children Will Have Pectus Carinatum?

It sounds like from your description that you have isolated PC. If this is the case then there’s a low chance that your kids would have PC too. Because it is isolated PC and not associated with a condition like Marfan syndrome, we can’t put an exact number on this chance.

Human inbreeding Neanderthal

-A curious adult from Mexico

May 24, 2016

First let’s make sure we’re on the same page when it comes to inbreeding. It basically happens when two close relatives, like an uncle and a niece, have kids together.

There has been inbreeding ever since modern humans burst onto the scene about 200,000 years ago. And inbreeding still happens today in many parts of the world.

Measuring Inbreeding

So how do people measure inbreeding? For example, how do we know if our parents (let’s call them John and Jane) are closely related?

If we have John and Jane’s family trees, we can answer this question. We look at how far we must go back in their family trees before we get to a common ancestor.

Does Inbreeding Matter?

Finally, why should we care about inbreeding? Because the children can end up with serious problems. To understand why, we need to step back and talk about genes.

Genes are stretches of DNA that each have the instructions for one small part of us.

They are like individual recipes in the cookbook that is our DNA. We have genes for eye color, blood type, and many other important traits.

Remember we have two sets of DNA, one from mom and one from dad. This means we actually have two copies of our genes too.

Making viruses that attack other viruses

-A high school student from Ghana

May 17, 2016

We can’t make a virus that works like our immune system. But we just might be able to make one that works a bit like the immune system in some bacteria. This system is called CRISPR.

Bacteria basically use a very simple immune system that finds the DNA of viruses and cuts it into pieces. When the viral DNA is cut, the virus can’t make new viruses. It is dead.

The guide RNA travels through the cell looking for a DNA that has those 18 bases. To get the CRISPR/Cas system working, the DNA and RNA must match at all 18 bases (click here to see how this matching works). If they don’t match, the RNA will keep looking. 

This is important because if the RNA matches any DNA in the bacteria or patient, then CRISPR/Cas will cut that DNA too. This can mess up the bacterial or patient’s DNA causing problems.

Using Viruses to Cure Diseases

In some ways, a form of killer viruses are being used in real life!

For some diseases, such as sickle cell anemia or cystic fibrosis, we know that there is just one gene that causes all of the problems. It has a mistake in it that we can’t fix (at least not right now).

What if we could get a fixed copy of that gene into the cells that need it?  Scientists are working on this right now and are using viruses to deliver the fixed gene.

Mom and daughter do not share same relatives

-A curious adult from Colorado

May 12, 2016

You can be related on a family tree but see no shared DNA. (BroderickFlickr)

In this image, each pair (except for the X and the Y) are represented by a long rectangle with a pinch in the middle. So each rectangle is actually a representation of a pair of chromosomes.   

The DNA I share with this relative is that little blue box on chromosome 7. That is all of the shared DNA that this test can see.

Since this is a light blue box, this means that the DNA is only on one of the chromosome 7’s in this pair. This is what they are trying to tell you with the term “half-identical.”

We Get Half Our DNA from Mom (and Half from Dad)

As I said, for the most part, our chromosomes come in pairs. One from each pair comes from mom and the other comes from dad.

This means that when we have kids, we pass only one from each pair to our child. And the one the child gets is chosen at random.

Let’s imagine that your mom has the same pair of chromosomes that I showed earlier:

Why CRISPR is revolutionary and how it works

May 4, 2016

-A curious adult from California

CRISPR is a game changing DNA editing tool that has already revolutionized biology and may be set to do the same for medicine. It is a game changer.

What makes it such a breakthrough is how easy it is to program it to go to a specific spot in a cell’s DNA (its genome). This is quite a feat given that the right spot is somewhere in the six feet of 6 billion microscopic DNA letters scrunched together inside of a microscopic cell.

Getting There

DNA is made up of four bases: A, G, C, and T. The instructions for you are written with a long string of 6 billion or so of these four bases.

CRISPR relies on something Watson and Crick figured out back in 1953—A always pairs with T and G with C. This underpins why a cell can easily copy its DNA when it gets ready to divide, how a cell reads its genes and lots of other aspects of how a cell works.

Getting More Efficient

If CRISPR could do this in most cells, we’d be able to cure a whole lot of genetic diseases. But it can’t.

It takes real effort to get 5% of cells to have their DNA changed in the right way. And when that happens, often many more cells have damaged DNA instead of edited DNA.

So the next steps are really to get more cells with changed DNA and fewer cells with damaged DNA.

half siblings with common dad DNA sharing

-A curious adult from Illinois

April 22, 2016

You are more likely to have more DNA in common with your half-sisters than with your half-brother. But this is not a for sure thing. It is definitely possible that you happen to share more DNA with your half-brother.

The usual satisfying genetics answer right?

It turns out that half-siblings share 25% of their DNA on average. But this is only an average.

X Really Does Mark the Spot

First let’s go over the easy part—why half-sisters with a shared dad have more DNA in common on average than does a half-sister and half-brother.

For this we are going to just focus on the X and Y chromosomes. Here is an image that tries to show what each parent’s X and Y chromosome pairs look like:

Mixing and Matching

In the last image, each parent passed down a whole chromosome. So mom 1 passed her green chromosome down to her son and so on.

What this means, of course, is that the brother and sister, your half-siblings, end up sharing no DNA on their X chromosomes because she got the black X and he got the green one.  Reality is a bit more complicated and is more like this:

Typos in the Genetic Code: How Much Should They Matter?

Unlike this engine, there are some seemingly important parts in our DNA that some of us are fine without. (Wikimedia Commons)

Mosaicism with X and Y

- A curious adult from Florida


April 6, 2016


Your chromosome arrangement or karyotype is indeed rare enough that it doesn’t have a name. One study said that there have only been 10 or so reported cases. This is really rare!

Greenwood Genetic Center

Chromosomes come in pairs because we get one of each from our mom, and one of each from our dad. Sometimes, though, someone can have three copies of a chromosome instead of two.

Here's an example of what one of these kinds of karyotypes might look like:


Sometimes people have cells with different sets of chromosomes. Some of their cells have one set and the rest have a second set. This is called mosaicism.

This is what you are describing. Some of the cells are 47,XXY (Klinefelter syndrome) while some others are 46XX, the karyotype of a typical female.

Genetics does not match eye color

-A curious adult from California

March 30, 2016

You have hit on a big problem in this new genetic age. While we can easily take a peek at our DNA, we don’t always understand what it means.

See, the two SNPs they use are a big deal in deciding between green and blue in people with non-brown eyes. But they are not the whole story. Many, many SNPs play a role in determining your eye color.

How SNPs Affect How a Gene Works

So how do we know that certain SNPs relate to different color eyes? Scientists can look for relationships between the letters someone has and the traits they have.

For instance, maybe they see that people with a G at that position usually have blue eyes. And maybe they see that people with a T at that position usually have green eyes.

Very often we don’t know why a SNP causes a trait. We just know that people with that SNP for some reason have that trait.

Genes Don’t Work in a Vacuum

As you know from perusing the 23andMe site, there is more than one SNP that affects eye color. And these SNPs can be in different genes.

All the genes that affect eye color aren’t just working by themselves. They can all affect each other too.

This makes it hard to make predictions even with known SNPs/genes. Throw in a bunch of unknown SNPs that can affect eye color too and you begin to see what we are up against with predicting even something as seemingly simple as eye color.