Squibs
Definition
A Squib is defined as a person born into a wizarding family with absolutely no magical powers at all.
how?
Earlier we discovered that the allele that codes for wizards is a recessive allele. Therefore, if two parents are both wizards and witches there is a 100% that their offspring will get the recessive allele. If that is the case, then how are there squibs?
epistasis!
Epistasis is when the expression of one gene depends on the presence of one or more "modifier genes" (Cordell 2002).
So what if Squibs genotype has the epistatic gene? Their parents genotype would have to be something like:
wwBb*wwBb
Where the ww stands for the homozygous recessive wizard genotype.
and Bb stands for the Epistatic heterozygote for the squib gene. This means that the parent is a carrier for the squib gene but it does not mask the wizarding allele. If the offspring were to receive both recessive alleles for the epistatic squib gene, then the gene will mask the wizard gene and the individual will not have any magical powers.
So what if Squibs genotype has the epistatic gene? Their parents genotype would have to be something like:
wwBb*wwBb
Where the ww stands for the homozygous recessive wizard genotype.
and Bb stands for the Epistatic heterozygote for the squib gene. This means that the parent is a carrier for the squib gene but it does not mask the wizarding allele. If the offspring were to receive both recessive alleles for the epistatic squib gene, then the gene will mask the wizard gene and the individual will not have any magical powers.