blood group

[jannyneve]

how likely would it be for brothers to have the same blood group?

[bobjim1705]

It depends on the parents' blood type.
Each parent contributes to their childrens' bloodtype, giving half each.
Both Group A and Group B are dominant over group O. If someone is group A, then they are either AA (A from both parents) or AO (A from one, O from another.)
A and B are codominant, so a child with AB would have had to have one parent with type A (AA or AO) or B (BB or BO.)

The likeliness of a particular blood group is heavily dependent on your parents' types, and furthermore, their parents' types to, to determine whether or not their blood type is AA or AO (although both are still A.)

[Peter Pedant]

No it can be calculated.....

If you just give a unit of blood to someone else, the chance is 50% it will be compatible.

This is related.....

If there were just two blood groups, M and N and one was 90% incident and the other 10%

then no matter who the parents are ! The chances are that boths sibs will be M and concordant....around 80%

I'll think about it....

[gen2]

If both parents are homozygous, then the chance of two brothers having the same genotype is 100% hence 100% chance of the same blood group.

If one parent is homozygous and the other is heterozygous then there is a 50% chance of having the same genotype. This does not translate into the same percentages of phenotypes since the alleles A and B are both dominant over O (eg AO and AA are different genotypes but the same phenotype = group A)

If both parents are heterozygous then the chances may be 25%, 50% or 75% that they have the same bloodgroup depending upon each parent's genotype.

In reality the commonest genotype is the homozygous recessive combination OO. All children of parents with this genotype will be group O.

I know this doesn't answer the original question because it depends upon the relatine occurrences of each genotype in the population and it will need someone with a better grasp of statistics to work it out but I hope this goes some way to helping.

[Peter Pedant]

Remember that A is not compatible with O, but A can receive O yet O cannot receive A.

The problem of working out if a population is AO or AA is not that difficult - Take the blood groups to be

0 - 44% A 42% B 12% AB 2% - it is around about that for Northern Europeans. Your 42% A is made up of AO and AA genotypes.

However O is OO and so if the genotype (p-squared) is 44 then the gene frequency is the square root of this (p) and I have taken this to be 2/3 - [0.67] . A per cent is less than one and squar roots of numbers less than one are greater than the number.The square root of 0.4 is around 0.6

We know can conclude in a mixed population that in your 42 % A one two thirds is AO and one third AA., to wit 28 and 14 - adding you will notice up to 42

der daaah

so now - after all you have to do something - make up a matrix 6 x 6 with O, AO,AA,BO,BB,AB along the top and down the side. In the box OO OO, this will occur 44% x 44% of the time, about 16% and all will be compatible so write 16%.

In the O AO box - I reckon 50% are gonna be compatible. and this pairing occurs 44% x 28% which I think is around about 10% so in this box, write 5% because only half are going to be compatible....

HA HA I will let you fill in the other 34 boxes !!

then you add up all the perdentages....

I still reckon is gonna be around 50%

Have a good week-end.