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The Rh Blood Type System
Related Article: Rhesus Disease
When we are told our blood type, it is usually expressed as a letter followed by either a positive (+) or negative (-). This + or - refers to the Rh system of blood
The Rh system is actually much more complicated than the ABO system because there are more than 30 combinations possible when inherited, however for general usage, the Rh proteins are grouped into two families - either positive or negative.
As with the ABO system, there is a dominant allele which happens to be the positive family. This means that the genetic pairs that can exist in humans are as follows:
|Genetic makeup||Blood type|
The same inheritance rules apply as on the previous page:
|Parents' Rh types||Possible allele combinations||Possible Rh in the children|
|Both +||++ & ++||++||positive|
|Both +||++ & +-||++ or +-||positive|
|Both +||+- & +-||++ or +- or --||poitive or negative|
|Both -||-- & --||--||negative|
|One + & One -||++ & --||+-||positive|
|One + & One -||+- & --||+- or --||poitive or negative|
Rh negative children can have parents that are either Rh positive or Rh negative.
If both parents are Rh negative then the children will be Rh negative.
1. What is a blood type?
2. How blood types are inherited
3. The Rh blood type system - positive or negative
4. Paternity testing and blood types
5. Examples of blood type inheritance
6. A quick history lesson
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