O is the blood type of around about 47% of caucasians.

 

O is also recessive.

That struck me as a high figure for a recessive gene.

Also AB is at 5%, that struck me as low.

 

What causes this?

I asked my lecturer and he hummed and haaahd, and said it

was "a result of the inherent strength of type O".

(In other words he didn't know.)

 

Cheers.

i cant remember the name of the phenomenon (hasselmain?) but its basically that its resessivness allows it to hide.

 

eg imajine Ao X Ao, their offspring would be

 

AA, Ao, Ao, oo 3:1 phenotype ratio in favor of A, but 1:1 allele ratio.

 

now imagine for example Ao X Bo, to give the offspring

 

AB, Ao, Bo and oo. there is a 1:1:1:1 phenotype ratio but a 2:2:4 ratio of A:B:o alleles.

 

so the o allele, by means of being able to resessively 'hide', is present at a higher rate in the population and so the chance of 2 o alleles coming together is not as unlikely as it sounds.

 

its more elagantly, and also more extremely long windedly, explained with maths. if someone can remember the name of the equasion (hendelman-hasselbach equasion?)

It seems from the phrasing of the original statement "O is the blood type of around about 47% of caucasians." that husmusen meant 47% had oo as their genotype.

 

I don't know about this specifically, but think about the Norwegeins who are mostly blue eyed, yellow haired, both of which are recessive. Recessive genes aren't necessarily rarer, its just because of the inherent strength of type o In other words I don't know either.

 

 

A quick bit of research shows (wikipedia isn't a real source I know, but its good enough)

 

Type O people have red blood cells with neither antigen (that type A or Bproduce ), but produce antibodies against both types of antigens.

 

So I'm guessing from that information that type O is better immunised against various diseases because they have more antibodies (even if it is only against 2 different types)

Well, since blood transfusions are recent, we can assume there was no major selective value to having type O blood in the distant past. This leaves non-selective evolutionary mechanisms. The two I see as most possible for this are:

 

1) genetic drift. Since it'd be a neutral trait in the past, the gene frequency would fluctuate randomly, due to random events determining who lives or dies, who mates and how often. So, basically, it could be the product of simple random chance.

 

2) Founder effect / genetic bottleneck. If there were an unusual number of humans with type O blood in the initial group that colonized Europe, the gene frequencies would be higher due to that (with drift acting over subsequent generations). Alternatively, if a few individuals became highly geneticly productive (possibly while others died, such as during a famine or plague), there would be a genetic bottleneck in which a disproportionate number of type O individuals founded the future of the populations, resulting in a spike in gene frequency.

 

So basically, it's probably just random chance.

 

Mokele

Like Deathby pointed out, recessive genes aren't neccessarily 'supposed' to be rare at all, some conditions like polydactyly and achondroplasia are dominant genes, but the vast majority of people's alleles for those traits are homozygous recessive.

 

Just out of curiosity, how did the frequencies of different blood types (ie 47% O, 5% AB, etc) compare between races? Are they more evenly distributed in some races than others?

Auburngirl:

During my searches on the other info I found some interesting

sites, the following should give you a very lucid idea of

the global variation

 

Blood type variation maps.

Cheers.

I appreciate the link, I thought the patterns shown on the maps were really interesting. Thanks!