Genes and obesity

-A curious adult from India

Genes don’t usually cause obesity. But they can sometimes make it harder for some people to keep a healthy weight.

Some genes can affect obesity by influencing what decisions we make. If you have a set of genes that makes you crave sugar more than your friend, you may struggle with your weight more than he does. Or if your genes make you hate exercise, you might be more likely to end up heavier than you’d like to be. 

Why Does Obesity Happen?

If being obese is unhealthy, why are our bodies able to get overweight in the first place? Why doesn’t our body choose to not take in more food once it has enough? One of the leading theories called the “thrifty gene hypothesis” tries to answer this.

Long ago, before we were farmers, food was hard to come by during some parts of the year. Long winters and/or droughts meant that people had to be ready to starve some of the time.

Are There “Obesity Genes” in Other Animals?

In lab animals such as mice, each gene can be modified in an experiment to study what they do. A gene called ob is a famous example.

Mice with mutations of the ob gene cannot make a hormone called leptin. Leptin signals to the mouse’s brain that it is full and should stop eating. Mice with copies of ob that don’t work properly can weigh up to three times as much as a healthy mouse! 

Third generation clone worse than original

-A middle school student from Italy

July 5, 2016

No, it almost certainly won’t! Depending on your “starting” cell, a clone from the clone of a clone might just be a bag of mutations on the brink of dying from cancer.

This might all seem weird since the word “clone” usually means a creature that is completely identical to the original. But it turns out that a clone isn’t really identical.

DNA and Mutations

DNA is the instructions for making a living thing. We have one head, two arms, and all the things that make us human because of these instructions. There are also instructions that keep our cells from turning cancerous, give us our eye color, and lots of other things that makes each one of us unique.

When a mutation happens, it might change these instructions. This could be a really big problem!

Shortened Ends Means Shortened Life?

Inside the cell, DNA is packed into bundles that we call chromosomes. Telomeres are pieces of DNA at the ends of chromosomes that protect the DNA from getting damaged there.

Think of telomeres as “caps” for DNA. Every time DNA gets copied, the telomere “caps” get a little bit smaller.

As you grow older, the telomeres on your DNA keep getting shorter. Once telomeres become too short, they can’t protect your DNA anymore.

Chimeras are not more likely to have chimeric children

-A high school student from Denmark

June 27, 2016

No, the children of chimeras are not automatically chimeras themselves. In fact, they aren’t any more likely than anyone else to have kids with chimerism.

This is because each sperm or egg will have DNA from only one of the “twins” that makes up a chimera. The DNA from both twins does not mix in a single sperm or egg cell.

There are two sets of cells in a chimera, each set with their own DNA. And only one sperm fuses with one egg.

Here I’ve colored each of the fraternal twins a different color (blue & red). So during the same cycle, two of mom’s eggs are fertilized by two different sperm.

Things go a little differently with chimeras. Instead of growing up as two separate people, you end up with one person with both sets of cells. Here is what that looks like:

So what is essentially happening is two siblings are fusing together to become one person. Or to put in another way, you have a person who has some cells from one sibling and the rest from the second.  

Whereas mixing blue and red paint makes purple paint, this is not the case with a chimera’s cells.  There are some blue cells and some red ones. And fusing the two does not make a clump of purple—each cell has DNA from its original fertilized egg (blue or red).

hypertrophic cardiomyopathy genetics

-An undergraduate from Australia

June 22, 2016

Hypertrophic cardiomyopathy or HCM is a common heart condition (about 1 in 500 people has it) that is often genetic. But how it is passed down is not so simple.

The Nuts and Bolts of HCM

One such problem is the condition you asked about, hypertrophic cardiomyopathy (HCM). Let's break down those words so we can understand what that means:

Passing Down HCM

Alright, enough ancient Greek and physiology, now back to those genes!

There have been a handful of genes found to cause HCM. They are all instructions for the different pieces that form cardiac muscle and help to keep it organized and working right. If there's a change in one (or more) of these genes then the heart muscle can get disturbed so that over time it grows thicker and thicker.

Range of shared DNA between relatives

-A curious adult from Illinois

June 15, 2016

You could definitely share less than 25% of your DNA. In fact, most nephews share a bit more or less than 25% of their DNA with their aunts or uncles.

Having said this, 16% is starting to get pretty far from 25%. This doesn’t make it impossible, just less likely than say 24% or even 20%.

The Farther Away, the Wider the Range

You got half your DNA from your mom and half from your dad. This is pretty much the only relationship that is almost always an exact number like this. (Click here for one of the rare exceptions.)

Other relationships will share an amount of DNA around an average amount. And the further you get away from a relative, the wider that range can be.

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: