When it comes to genetics, many people assume that siblings who share the same parents often have the same blood type. But is this really the case? The short answer is... not always. While siblings inherit their genes from the same parents, blood type inheritance follows specific genetic rules, which means that not all siblings will have the same blood type.
But wait, what about twins? We'll get to that, but first, let's discuss how blood types are inherited.
How Blood Types Are Inherited
A person's blood type is determined by two genes, one inherited from each parent. So does that mean that you and your sibling, or siblings, automatically have the same blood type if you share the same parents? Or that your children have the same blood type? Nope!
Just like eye color, dimples or whether cilantro tastes like soap, a person's blood type is dependent on variant forms of an inherited gene called an allele. Because of these variations, a child of parents with blood type A, for example, might be type A or O.
Check out the blood type inheritance table below to see how blood types are passed down in your family:
Do Twins Have the Same Blood Type?
The genetic principles behind blood type inheritance apply to twins as well, but whether twins have the same blood type depends on whether they are identical or fraternal. Let's break down how this works for the two main types of twins.
Identical Twins
Identical twins, also known as monozygotic twins, are the result of a single fertilized egg splitting into two embryos. While there have been reported cases of genetic mutations that have led to differentiated blood types among twins, these are exceedingly rare. Generally speaking, identical twins are born with exact same genetic material, including the genes that determine blood type, so yes, identical twins have the same blood type.
Fraternal Twins
Fraternal twins, or dizygotic twins, are the result of two separate eggs being fertilized by two different sperm. This makes fraternal twins as genetically similar as any other siblings, meaning they share about 50% of their DNA. As a result, they can inherit different blood types, just like regular siblings.
In short, fraternal twins do not always have the same blood type. They might share a blood type, but they are just as likely to have different blood types depending on the specific genes passed down to them.
