|MadSci Network: Genetics|
The short answer is that it is almost impossible to calculate the chances. The grand and simple explanation is that there are multiple genes involved and multiple possible ways in which expression of different genes can result in diabetes. Simple Mendelian genetics of inheritance can help explain, however, why both of your maternal grandparents have diabetes, their children do not but you are still at risk. Let's postulate that there two genes, for either there is an allele that can cause diabetes. Call the genes A and B and the alleles (g) (good) or (d)(diabetes) A person has two alleles for each gene so for each they can be (gg), (dd), or (gd) - but only (dd) results in diabetes. So one maternal grandparent would be A(dd)B(gg) and the other A(gg) B(dd). Mendelian genetics would say that their offspring would all be A(gd) B (gd). Since the (g) allele cancels out the (d) allele, none of your maternal grandparent's children would have diabetes. However, that (d) allele is still there! Now, take a look at your father's side of the family. Yes, none of them have diabetes. BUT, are they homozygous or heterozygous for A or B? Remember, that (d) allele can be there but you won't see diabetes unless both alleles are (d). So if, by chance, your grandparents were heterozygous for either A or B than your father could be A(gd)B(gg), A(gg)B (gd) or A(gd)B(gd). Combined with your mother being A(gd)B(gd), there are a number of ways in which you could end up have two (d) alleles for either A or B, in which case you could end up with diabetes even though none of your parents have diabetes. BUT, the reality is that diabetes is controlled by more than 2 genes - in fact, from what I can determine by searching on PubMed we don't know how many genes are involved. It could be hundreds. So we can't calculate come up with a mathematical number to tell you what the chances are you could be diabetic. We can only tell you that yes, there is some risk. I wish I could be more definitive and give you a better answer, but I can't.
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