Basic PKU Genetics

PKU is a Genetic Disorder. 

It's literally a mistake in the DNA causing a mutation of sorts to occur.  This mutation happens in the PAH gene.  Usually the gene converts phenylalanine into nutrients we can use.  Ours can't. 

The mistake is genetic.  That means it carries on down the generations from parent to child.  It is also recessive.  It needs both parents to "carry" the gene in order for it to be apparent in the child.  If one parent is not a carrier, then the gene is smothered by the dominant gene.

So to get a PKU kid you need each parent to be a carrier.  Simple. 

But what happens when the PKU kid grows up and starts their own family?  What happens to the genes then? 

Well, that depends on the person they are marrying.  I drew a couple pungent squares to illustrate the concept.  (excuse my not so good pictures)

First off:

• The non-PKU gene is a "X"
• And the PKU gene is a "x"   

A non carrier will have "XX"
A carrier will have "Xx"
A PKU'er will have "xx"

First diagram: If a PKU'er marries a PKU'er

 

Looking at the diagram you can see that each kid will have a 100% of having PKU.

 

 

Second Diagram: If a PKU'er marries a Carrier

Looking at the square you see that each kid will have a 50% chance of having PKU and a 50% chance of being a carrier.

 

Last Diagram: If a PKU'er marries a Non-Carrier

Each kid will have a 100% chance of being a Carrier.

 

Now, look at the way I worded each chance.  "Each kid."  It's like rolling a dice.  If you get a 6 on one roll, does that mean you can't get a 6 on your next roll?  No.  For each and every child there is the same amount of chance that they will have PKU as they will be a carrier (at least if you marry a carrier). 



So, basically.  Those are the statistics for a PKU'er who decides to get married and have a family. 

Genetics is fascinating.   

Have a wonderful week!