Commonly Asked Questions

Over the years we have been asked many questions. Here are some of the most common we receive.

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DNA Basics
Basic genetic principles that may help you understand more complex questions

What are genes?
Click here and here to learn more about how genes have all of the instructions to make an organism, how they make proteins, and how they are related to chromosomes.

What is "junk DNA"?
Click here to learn how this isn't actually junk! These regions of the DNA are very important for turning genes on and off.

How do mutations cause disease?
Click here to learn more about how new changes in DNA can lead to problems.

What is recombination?
Click here to learn recombination is an important process that can help repair broken DNA, and help shuffle the DNA when making eggs and sperm.

What does dominant vs recessive mean?
Click here to learn more about how one trait can overpower and hide another, here to learn why some are dominant, here to learn how to determine if one version of a gene is dominant, or here to learn why the dominant trait is not always the most common one.

Why am I the only colorblind person in my family? 
Click here to learn more about the genetics of colorblindness, why it is more common in men than women, and how it can skip generations.

How do scientists figure out what gene controls a trait?
Click here to learn how scientists figured out a key gene in eye color!

How can tests like 23andMe link genetic markers to a disease?
Click here to learn how scientists can use your DNA to figure out how likely you are to get a certain disease.

Why can't genetic tests predict certain diseases, like type 2 diabetes?
Click here to learn how some disease are hard to predict because they are caused by a lot of different genes along with environmental influence.

How does radiation damage DNA?
Click here to learn how UV radiation in sunlight can cause mutations.

Why don't identical twins look the same?
Click here to learn how DNA isn't everything, and why your environment also matters.

Everyone else in my family has attached earlobes. Why are mine hanging?
Clik here to learn how this is actually a more complicated trait than we were taught in school.

 


 

Blood Types
The genetics of blood type and how it is inherited

What are the most common blood types of a child from any two parents?

How does blood type work?
There is one gene that determines the ABO part of blood type. This gene comes in three versions -- A, B, and O. Each of our two copies of this gene can be different versions. Click here to learn more.

Can two positive parents have a negative-type child? 
Click here to learn about Rh factor, and why it is common for positive parents to have negative children.

Why do Rh- mothers have pregnancy risks?
Click here to learn why Rh negative mothers who are carrying an Rh positive baby are at risk for hemolytic disease of the newborn (HDN), and how it can be prevented with RhoGAM.

 

 

My question wasn’t answered by this!

If the table says you can't have the blood type that you have, don't jump to any conclusions! There are documented examples where these rules are broken.

Can two O parents have a non-O child?
Click here to learn how this is possible by rare mutations.

Can an AB parent have an O baby?
Click here to learn how this is possible with a rare cis-AB blood type. 

Can two A parents have an AB child? (Or, can two B parents have an AB child?)
Click here to learn how this is possible with blood chimeras.

Can an O parent have an AB child?
Click here to learn how this is possible with blood chimeras or Bombay blood groups.

What is the Bombay blood group?
Click here to learn more about how an O parent can have an AB child with this rare blood type. 

Can two Rh negative parents have an Rh positive child?
Click here to learn how Rh tests are not always accurate.

How does cis-AB work? 
Click here to learn more about this rare blood type, and here to learn how mutation and recombination can cause this.

What are blood chimeras? 
Click here and here to learn more about this.

Can mutations cause some of these unusual cases? 
Click here to learn more about how mutation and recombination can lead to unexpected blood types.

How did blood type evolve in humans? 
Click here to learn more.

 


 

Eye Color
The genetics of eye color and how it is inherited

(Image from Pixabay)

What eye color will your children have?
Click here to try out a calculator that predicts eye color in most cases. Click here to learn more about the genetics of eye color.

Can blue-eyed parents have a brown-eyed baby?
Click here to learn how that is possible, and how most eye color predictions (like the one above!) use a simplified model that does not always apply. For a deeper dive into the genetics, click here.

Are all people with blue eyes related?
Click here to learn how this is mostly true.

Why are blue eyes uncommon?
Click here to learn why blue eyes are becoming less common.

Why do blonde hair and blue eyes tend to go together?
Click here to learn more about how these two traits are linked.

 

 


 

Other Traits
The genetics of human traits
 

Is a person born gay, or is it a learned behaviour?
Click here to learn how this is not a choice for most people, and how it is not possible to "unlearn" your sexual orientation.

Is bisexuality something that is taught, or it is something that is natural in a person's genetics such as being gay or straight?
Click here to learn more about to biology of sexual orientation, and what we currently know.

Is the ability to wiggle your ears genetic?
Click here to learn how this is actually not a very well studied trait!

Why do mosquitos like some people more than others?
Click here to learn why some people taste better than others!

Is intelligence more of a genetic or environmental trait?
Click here to learn how IQ of a child is very unpredictable, that this trait is influenced by many different genes, and how environment is very important.

Are anxiety disorders genetic?
Click here to learn about how anxiety is shaped by both genes and environment.

 


 

Relatedness
Questions about DNA tests and predictions of how related you are to someone else

What is the best test to tell if two people are related?
Click here to learn about genetic tests.

Why do the results from my genetic test give me an inexact percentage?
Click here to learn why these tests might show you a different percent relationship than expected.

How likely are tests from Ancestry.com or 23andMe to detect distant cousins?
Click here to learn about how sensitive these tests are at picking up on relatedness.

Where do these percentages come from? Why do I share 50% of my DNA with a full-sibling, but only 25% with a half sibling?
Click here to learn about heredity, how much DNA you inherit from each parent, and how that relates to % relatedness.

Is it possible to detect incest in a genetic test?
Click here to learn if you can tell how related your parents are from these tests.

What genetic information does a father pass on? 
Click here to learn how you get more DNA from your dad than just a Y chromosome

What are the risks in marrying your cousin?
Click here to learn about how the risk for genetic disorders is only slightly elevated for the children of first cousins, and here for how the risk is even lower in first cousins once removed.

Still confused? Just want to know more? Click here to order our latest book, A Handy Guide to Ancestry and Relationship DNA Tests.

 


 

Ancestry
Are you confused by your 23andMe or Ancestry.com results?

Why don’t my sibling and I have the same ancestry results?
Click here to learn how different siblings may have slightly different results. Even though you both have 50% of your DNA from mom and 50% from dad, it may not be the same 50%

Why don’t identical twins have the same ancestry results?
Click here to learn more about how people with the same DNA can get different results.

My ancestry percentage doesn’t make sense! Why did I get this number?
Click here to learn more about how these tests calculate these numbers.

Why are mitochondrial DNA and the Y chromosome good for detecting distant ancestry?
Click here to learn more about how mitochondrial and Y DNA can be used to detect more ancient ancestry.

How can tests like 23andMe link genetic markers to a disease?
Click here to learn how the disease risks are determined by these companies and how genome-wide association studies (GWAS) work. 

Still confused? Just want to know more? Click here to order our latest book, A Handy Guide to Ancestry and Relationship DNA Tests.

 


 

Other cool stuff
Things that don't fit neatly into the other categories.

What is CRISPR and why is it so great?
Click here to learn how CRISPR/Cas9 is a revolutionary genome editing tool that is changing modern biology. Click here to read an older article on how hard it used to be!

Are genetically modified foods bad for me?
Click here to learn how GM foods are generally safe, and here to learn more about why labeling foods as GM might not be a great idea.

Would it be possible to bring back Neanderthals?
Click here to learn how this might be possible, and here to learn more about de-extinction and how we may be able to bring back wooly mammoths.

Could we grow an organ in a lab?
Click here to learn more about how scientists are still working on this.

Could we use gene editing to regrow a limb?
Click here to learn why this may be possible far in the future.

Could we bioengineer immortality?
Click here to learn why aging is a hard problem to solve.

How can chimps and humans have different chromosome numbers?
Click here, here, or here to learn more about chromosome number can change in the course of evolution. And click here for some information on chromosome number in our distant cousins, the Neanderthals and Denisovans.

Why are zebras black and white?
Click here to learn how stripes are actually hard to make.

What kinds of careers can you have with a biology degree?
Click here to learn about different types of jobs you can do with a biology degree, what kinds of degrees are available in biology, and what education level you need for various career paths. Click here for a flowchart of what careers you can pursue in genetics, organized by minimum required education level.

 

Want to learn all sorts of other cool facts? Click here to order our book, When Will Broccoli Taste Like Chocolate?: Your Questions on Genetic Traits Answered by Stanford University Scientists.


 

Question not answered?

Browse through our archive of previously answered questions here.

Still can't find what you're looking for? Submit a question to us here. While we can't answer every question we receive, we do our best to respond.

 

 

 

 

 

 

 

 

(Adapted from Wikimedia Commons)

(Image from Wikimedia Commons)

 

 

 

 

 

(Adapted from Pixabay image)