Blood Types + Genetics:
A Brief Introduction

Human genes provide the blueprint for our makeup. they determine whether we are tall, short, fair, dark, smart or slow. All genes come in pairs - one from our mother, the other from our father. There are different types of genes that our parents can contribute to these pairs. Some genes are "dominant" and some "recessive" - the difference being that if a dominant and recessive gene are paired up, the dominant one will be expressed. The recessive one will only be expressed if there are two recessive genes in a pair. Think of it like "strong genes" and "weak genes".

The O allele (or gene) is recessive. A and B are dominant. So if your father gives you an O and your mother gives you a B, you will have blood type O. Your gene combination will be OB (this is called your "genotype") and this will be expressed by you having blood type B (this is called your "phenotype"). Learn more about Genotypes and Phenotypes here.

No because both A and B are dominant, when you get both an A and a B in your gene pair, you will have blood type AB. See the table below for the different combinations of genes and the resultant blood group they produce:

Think you understand? So if your mother is blood type B and your father is blood type A, what will you blood type be? Well it could be just about anything! Your mother could have genotype OB and your father OA... so the pairs you could end up with are OO, OA, OB, or AB - all of which result in different blood groups! Try the Blood Type Calculator to work out your parents' or your baby's possible blood type.

Blood Group Frequency

There are thirteen blood group systems recognized at the present time1. However, the ABO system is of most important to us because it is the determinant of reactions in blood transfusions. These are also important factors for expectant mothers as sometimes her blood type is incompatible with that of her child.

Sources on the web provide blood type distributions for the "general population" - which I assume means Americans and/or Europeans. The distribution is more or less as follows:

This distribution pattern is not, however, necessarily what you'd expect to find in Singapore. There are various sources of information on the web that provide similar statistics for some of our neighbors though I caution to add that these might not be statistically significant samples:

There is a wonderful overview of blood type distribution available on the web (click map) which shows this distribution for the O gene (or "allele" which is the more correct term meaning "any of the alternative forms of a gene that may occur at a given locus" - ie the alternatives for the part of the gene we are concerned with).

As you can see, the distribution pattern in SE Asia doesn't look much different than that of western Europe (both are about 60-70%) although clearly Latin America has much more abundant supplies of O than anywhere. It may not seem like there is much difference between say 60% concentration of the allele and 70% concentration of the allele but because O is a recessive trait, blood group O results only when an individual has two O genes. So if there's 54% concentration of the O allele in Beijing, you could expect approximately 54%*54%=29% of people to be blood type O. Whereas in Hong Kong perhaps the O allele accounts for only 68% of the gene pool so we would expect 68%*68*= 46% of people to be blood type O.

Using the distribution tables above, one can estimate the percentage of O, A and B allele's of the sample population (using a quadratic equation while making certain assumptions about the uniformity of the data).  In this case, the percentages are:

This suggests that, versus the "general stats" in table 1, Asians have much higher incidence of the B allele while the A allele is less common. The O allele, however, appears roughly the same. With such simplistic models and unverified data, it is flawed to draw conclusions that are any more specific than these broad generalisations.

You even have to be careful about assuming that your statistics have now educated you about the blood distribution of Chinese people as a whole for this is a very diverse group...

ABO distribution among the Chinese
Sournce Link Broken

estimated allele percentages...

Transfusion Combinations

Blood type "O" is a "universal donor" - which means people with with type O blood can donate to persons with blood types O, A, B or AB. IE anyone! HOWEVER this gift to the world is not reciprocated and we can only receive blood from our fellow O donors.

Likewise, the absence of the RH protein is such that we can donate to both RH +ve and RH -ve persons but in return we can only receive blood from other negative donors.

Table of Receptivity

It is therefore truly fortunate to be born type AB +ve because you can basically receive blood from just about anyone. On the other hand, we O -ve types have a real problem.

Using the blood group frequencies in table 1 above, we can infer a "receptive index" (please don't quote me - I made this term up) which indicates the percentage of the population from which you can receive blood:

We can also infer this table for, say, the Malay population based on the data in table 2  however we must assume that the Malays are likewise  85% Rh+ve and 15% Rh-ve. This results in the following values:

So what's so Special about Singapore???

Looking at the information above, it looks like there should be no greater risk to be O negative in Singapore than in say Paris. But there is: Why?

While the distribution of O, A and B genes may be similar to Europe, the +ve and -ve characteristics are very different and in fact -ve blood is extremely rare. An SBTS doctor told me this:

Now consider the % of the various races in Singapore (1997: Stats Singapore):

And if we assume that all the "others" are Caucasian we can estimate the % of Singapore residents with -ve blood type. we can do a quick calculation to see that less than 2% of the population are -ve blood type. That would mean that in Singapore, the various blood groups would look more like this:

Producing a local "Receptivity Index" for each blood group as follows:

Clearly all the -ve blood types could be at risk in the case of a blood shortage. But fortunately, because of the vast numbers of people with +ve blood, it is unlikely that -ve blood will be disbursed frequently in emergency situations as it is in the States. As a trauma patient of unknown blood type will be from a +ve blood group, O+ve blood will usually be given.