Blood Types

I got quite the shock in lab class yesterday. We are working on blood right now and understanding the different types, you know the A, B, O, AB and the Rh (which is what makes it positive or negative). In lab we got the chance to test our own blood, and I was one of the 6 who chose to do so. It turns out that even thought both mom and dad have a positive blood type (O+) I have a negative (O-). I didn't even know that that was possible but Dr. Bishop (my Bio teacher) explained it for us.

Here is how it works; every one has two parts of their chromosomes (genotype) that decide weather the blood will be + or -. The (big) D is dominant and positive; and the (little) d is negative and recessive. Each person has two that make up a genotype. If someone has positive blood they are either DD (homozygous dominant), or Dd (heterozygous dominant), if they have negative blood it's dd (homozygous recessive). For two positive blood typed people to produce a negative blood type child they have to both be Dd. That would give them a 25% chance of having a negative blood typed child.

So both my parents are Dd. The dominant D makes them both positive Rh, but when I got one from each of them the ones I have are both d's, so I am negative.

---D d

D DD Dd

d Dd dd (me)

Red - Mom
Blue-Dad
Yellow-possible positive child types (75%)
Green - possible negative child types. (25%, me)

ABO Type Rh Type How Many Have It

O positive 37.4% 44%
O negative 6.6%

A positive 35.7% 42%
A negative 6.3%

B positive 8.5% 10%
B negative 1.5%

AB positive 3.4% 4%
AB negative .6%