Daily Prophet April 27th, 1996
Science Section
A Report of the Inherited Wizarding Trait and its Apparent Sporadic Appearance and Disappearance
By: Athalia Thumberdean
In the Wizarding world a majority of the witches and wizards are the offspring of at least one magical parent. However, there a several witches and wizards who are the offspring of two Muggles known as muggleborns and in reverse there are also several offspring of Wizarding parents who don't posses magical ability known as Squibs. How is this possible as for the most part magical ability seems to be an inherited trait? To answer this we most first understand the concept of genetics, the process of passing down traits during reproduction, and look at how the wizard genetic make-up differs from muggles.
First off, all living things are made of cells and inside the nucleus, or brain, of the cell there are chromosomes which are made up of genes. Genes are instructions for how the organisms is to look, for how to make essential organs, if the organism is to have any hereditary diseases, and in the case of wizards how to create humans with magical abilities. These chromosomes are extremely small and can only be seen with a very powerful microscope* or a strong Magnification charm and although the difference is miniscule, it has been discovered that Wizard chromosomes are on average ever so slightly larger than Muggle chromosomes. Why? Because they contain the chemical instructions that separates Muggles from wizards.
Another important thing to understand before we can answer the question is how the traits instructed in the genes can be passed down to offspring. All humans, wizards included have 46 chromosomes or 23 pairs of chromosomes; 23 come from the offspring's mother pair up with 23 from the offspring's father. To be a wizard the offspring must have the extra installment in all 46 chromosomes. How is this possible then in half-bloods and other mixed ancestry offspring. Well, in the extra wizarding part of the chromosomes there is instructions to do something (that does not always need to be done with "purebloods") while the offspring is being conceived. This is to create copies of itself and send it over to the Muggle chromosomes. The additional parts will attach themselves to the Muggle chromosomes causing them to become magical chromosomes and making the offspring a witch or wizard.
This explains how half-bloods and others of mixed ancestry are able to perform magic, but what about Muggle-Borns and Squibs? The cause of Muggle-Borns and Squibs is mutation. Mutation might sound like a derogatory and insulting explaination, but all it really means is that some chemicals in the DNA did not line up as they were supposed to and mutations, especially in the case of Muggle-Borns, are not always a bad thing. If two Muggles are reproducing and one of their sex cells is mutated so that its chromosomes have the extra wizarding addition then it will do the same thing a wizarding cell would do and send additional wizarding parts over to the other Muggles chromosomes and their child will be a witch or wizard. If a witch and wizard are reproducing and there is mutation with both of the sex cells so that they do not have the extra part, the child will be a Squib. This explains why Muggle-Borns are much more common than Squibs as it takes two separate mutations to make a Squib and one to make a Muggle-born.
This is the proven theory for why there are Muggle-Borns and Squibs and it has inspired another, controversial theory that many find rather interesting. It suggest that since it is very easy for Muggles to produce witches and wizards, all witches and wizards may be descended from Muggles and that we may all be technically Muggle-Borns. This is very possible and it is more proof of a valid point. Today, many witches and wizards boast that they are "pure-blood" and they go around calling Muggle-borns derogatory terms such as "mudblood" when it is highly possible that they too may be "mudbloods." In any case, it is almost certain that there aren't any "pure-bloods" anymore. The wizarding numbers simply aren't large enough and if they are truly pure-blooded they are probably inbred which, in my opinion, isn't much to boast about. I implore those in the Wizarding world who treat Muggle-Borns rudely and unfairly to consider this article and to stop with your prejudice tirade against them.
*A device muggles use to magnify very small things.