The Question is:
Should a mother be worried that their child is not theirs when both
parents are B-positive and the child is A-negative. The explanation
does need to include "positive and negative" with respect to blood
type. Just take into consideration the type itself such as A,B or O.

Thoroughly explain the answer. Draw tables (pundit squares),
illustrations to support your explanation. You must indicate that you
understand how the inheritance of blood type works. And why this is,
or is not possible.

Thanks for all your help.

-Vormav

---

Clarification of Question by vormav-ga on 11 Apr 2005 07:06 PDT

The Question is:
Should a mother be worried that their child is not theirs when both
parents are B-positive and the child is A-negative. The explanation
does NOT need to include "positive and negative" with respect to blood
type. Just take into consideration the type itself such as A,B or O.

Thoroughly explain the answer. Draw tables (pundit squares),
illustrations to support your explanation. You must indicate that you
understand how the inheritance of blood type works. And why this is,
or is not possible. Include if necessary terms such as homo/hetro
zygous, dyhybrid crosses, X-linked crosses.

Thanks for all your help.

-Vormav

Hi

If both the parents have blood groups B then the child either can have B or O.

possible Punnett Square are

             B    B
          
          B  BB   BB

          B  BB   BB

So the child has B in this case. But we have assumed in this case that
both the parents dont have a O alle. A blood group can be B if you
also have BO alles instead of BB alles. So trying the other
combination of one parent having BO and the other BB and viceversa,
and also a combination with both parents having BO alles, you will see
that the child can also have a blood group O (each O coming from each
parent).

So if neither of the parents have an A alle then the child cannot have
a A alle and hence cannot have a blood group A.

Hope that helps.

cheers,
prasad.

But just to complicate things a bit, evolution seems to suggest that
the blood type had to split at some point from 1 generation to the
next either during the human era or during the lives of the ancestors
of humans.

I'm no biologist, but I'm curious for a biology stanpoint answer... 
if humans started with 1 man and 1 woman of different blood types,
could that explain having the varying blood types we have today?

So the Punnett Square could not be:
    B    b

B   BB   Bb

b   bB   bb

B-B dominant blood type
b-A reccessive blood type
The parents could not be both heterozygous? Sorry I do not know much
about Biology. I am still kind of confused.

In response to  jack_of_few_trades-ga, Yes the female could be A/O+
and the male B/O- and in their progeny you could get A, B, AB and O +
or - (assuming they are prolific). It also works if one is AB+ and the
other is either A/O, B/O -, but then it takes until the F2
(grandchildren) to get the O blood type.

Regarding A, B, and O blood groups, both the A and B alleles are
dominant, whereas the O allele is recessive.
The A allele is denoted by "I^A", and the B allele is denoted by
"I^B".  The O allele is denoted with "i".
If someone has a B bloodgroup, then their genotype must be either
"I^B/I^B" or "I^B/i".  They cannot have an "I^A" allele as this would
contribute to an AB bloodgroup.
This is quite simply the reason why the A-positive child cannot belong
to two B-negative parents.  Punnet squares and illustrations here are
redundant because you just need to recognize the fact that the I^A
allele cannot be present in either of the parents, and hence there is
no way of it being transmitted to the child.

Thanks Dops!  I remember "learning" all this stuff back in high
school, but back then I really didn't care so nothing stuck with me. 
The info is quite interesting and useful now.

This is just answering jack-of-few-trades' question about the various
bloodgroups present in humans.
The reason why there are different alleles for a gene is that at some
point in human history, the gene underwent a mutation which resulted
in a new allele.  It is generally believed that news alleles arise as
a result of mutations.  Of course then new phenotypes can result
through recombination of different alleles (since it makes two alleles
of the genotype to make up the phenotype).

Check this site: http://www.classkids.org/library/classqa/bloodtyp.htm
it outlines the types and gives a chart showing what parents of
different types can produce together.  Two B- parents could never
(according to biology) produce an A+ child.  Note: Two RH- cannot
produce an RH+ but an RH- and an RH+ can produce an RH+.

no_pseudonym,

It still seems contradictory to me that biologists say that 2 parents
with this blood type cannot possibly have a child with this other
blood type... but then you're saying the gene can "mutate" and create
any result.

Has this mutation or anything similar ever been physically studied or
is this a theory that simply has to be the case in order to not
disprove evoloution?  I'm not trying to be obnoxious (although I know
these types of questions always sound obnoxious) but I'm really
curious.

(I'm assuming you are familiar with basic genetic terms such as
allelism, genotype, phenotype, etc.  If you aren't let me know and
I'll be glad to re-explain :-))

Your first question seems to be asking whether if initially a man and
a woman had two different alleles of a gene, whether this could
explain multiple allelism in subsequent generations (i.e. more than
two alleles, as is the case with ABO bloodgroups).  Say the man was
had an A bloodgroup (dominant) and the woman had O bloodgroup
(recessive).  At the time, there were only two alleles of the gene and
hence B bloodgroup or AB bloodgroup didn't exist.  The only possible
bloodgroups would be A and O.  But later on in time, a particular
individual may have had a mutated A allele which resulted in another
dominant allele, B.  The mutation could then be past on to the
progeny, and so long as it doesn't compromise chances of survival the
new allele will remain in the gene pool.  Hence, because of this
particular mutation, two dominant alleles exist (A and B), in addition
to the recessive O.  Hence the mutation ultimately means that future
generations can have four possible blood groups: A, B, AB or O.
I'm not sure if this is the precise pattern through which it occured
with humans (although I can confirm that new alleles arise only
through mutations).  Several experiments such as gene mapping studies
have shown that mutations are responsible for the emergence of new
alleles.
But remember that such mutations are very, very rare occurences, and
the mutation that led to mutiple alleles for bloodgroup probably
occured many, many years ago (perhaps even when humans were still
monkeys).  The chances of an identical mutation occuring again are
very, very slim.  What I'm saying is that if you had two parents with
B bloodgroup, the chances of a B allele mutating into an A allele to
produce a child with A bloodgroup would be infintestimally small.
As far as I know, it is becoming increasingly difficult to try and
disprove evolution.  There is even a saying that "nothing in biology
makes sense except in the light of evolution."  Remember that when
Darwin formulated his theory of evolution, he know nothing about
genes.  He based his theory on observations he made in the natural
world.  With breakthroughs in genetics, the theory of evolution has
gained much more evidence.  Most instances of evolution are impossible
to study as they occur over a period of hundreds of years.  However,
scientists have been able to study phenomena such as
antibiotic-resistance in bacteria.  Of course, ultimately evolution
cannot be 'proved' and hence it remains a theory, but in my opinion it
is a very logical, and well-grounded one.

i'm in my second year in collage and i'm studying biology and i can
tell you that's impossible. there are four different blood types A, B,
O, AB, each with the abilty to be positive or negitive.
if both the parents are just B then there are no genes for A present
for any of there children to have that blood type. all the children
could be is B or O.
This is because it takes two genes to make up a blood type, and to
make blood type B a person needs either two B genes or one B gene and
an O gene(B genes are "stronger" then O genes), Say both have O and B
genes, Then:
      
Dad\Mom|B  |O            See, only B and O are possible, for them to have a 
-----------------        child with type A blood one of the parents would
  B    |BB |BO           have to have type B blood with the O gene i.e. type BO
-----------------        and the other parent would have to have type AB blood,
  O    |BO |OO           which, as i said, is completely different from type  
-----------------        B.


Just to show you how it would work...

Mom\Dad    |B  |A        This makes type A possible (AO = type A). as i said
       -------------     if both parents are just type B or BO then to have a 
        B  |BB |BA       child with type A blood is immpossible, unless they
       -------------     adopt or there is a REALLY BIG F*%K UP at the 
        O  |BO |AO       fertillaty treatment clinic!
       -------------

Thanks Pseudo,

That all made since to me except the gene mapping showing that
mutations occured.  Did those experiments determine that
1) Mutations occured no matter what
2) Mutations occured if the origional pool for blood types weren't
sufficient to make all the types of blood their are today
3) Something else

I ask because I've read through many many findings (maybe 50% of all
biological reading I've ever done) that assume evolution and draw
conclusions from that assumption as well as their findings.  These
studies almost always give more support for evolution, but since their
basis was that evolution is fact (before doing the study) then they
don't carry any weight as far as supporting evolution.  But honestly
there are many debates for and against evolution which can be argued
to no end :) ...
As far as blood types go, it seems aparent that either 
1) Mutations occured... which you said is very very rare.  And if you
look at the human (or even monkey population that turned into humans)
we don't have all that many ancestors relative to the number of people
living today.
Today there are 6 billion people.  200 years ago there were 1 billion
people. 400 years ago it was 500 million people.  As you can see, our
ancestors weren't huge in number.  The further back in time you go,
the less likely such a mutation occured simply because we have fewer
ancesters from the given time.  It's conceivable that it happened, but
if it did then it will likely happen again and given the number of
people today who know their blood types, such a change should be
observed sometime.
2) The origional humans (or human ancestors) had the various types of
blood needed to create all the blood types that there are today.  Dops
suggested that "female could be A/O+ and the male B/O-" could create
all the blood types we have today in the following generations.

Honestly now, if you don't assume evolution or creation or any other
far fetched story of human origins, which one seems more likely?

I'm very curious about the gene mapping studies.  Do you have any
links about these explaining the evidence for a blood type mutation? 
I definately won't count these mutations out, but from the little I've
read... evolution seems to be assumed in order to have a need for a
mutation and therefore the mutation must have occured.  If there is
more to the mutation deal then I'd love to read more about it to find
out.

Hi, jack_of_few_trades-ga and no_pseudonym-ga 
 
From and evolutionary perspective, it seems to me that the most
parsimonious situation is that proto-humans were all AB+. Remebering
that random mutation is infinitely more likely to cause a loss of
function (recessive) than a gain of function allele (dominant),
mutation of either the A or B genes such that they no longer make the
antigen, would introduce the O allele (being a loss of function
allele) into the population. There would at this time however be no
individuals with an O blood type. If one assumes that the first
mutation was in the A gene, so that now A and O segregate in the
population, a loss of function of the B allele would allow the O blood
type to appear. The same is true for the RH factor as well, loss of
function of RH+ would give all the combinations. The mutation rate in
humans is high enough (some estimates are as high as 1.5 loss of
function alleles per zygote) that this could have easily occurred on
evolutionary time-scales.

With regard to the "theory of evolution." Evolution, classically
defined is a change in gene frequency over time. The example of
antibiotic resistence in bacteria is a nice example of how easily this
is measured and how evolution definately occurs in real-time. It is a
directly measureable process, not a theory or idea, but fact, like
gravity :). What is largely at issue is speciation or the origin of
humankind, often in my opinion inaccuratly referred to as evolution
(or Evolution).

Thanks Dops, that was quite informative.

"Remebering that random mutation is infinitely more likely to cause a loss of
function (recessive) than a gain of function allele (dominant)"
"Evolution, classically defined is a change in gene frequency over time."

It sounds from these statements you made that you see evolution as a
loss of function for the most part.  It's probably just the
terminology that makes me think this, but it stuck out to me so I
thought I'd bring it up.
  
Perhaps the case could be made that the mutation more often occurs in
the lesser genes making them recessive so that the greater genes can
have their way... but that would spark the question 'what causes only
the lesser genes to not so randomly mutate?'

I'd like your insight as to whether I'm way off base or if you have an
answer to that last question.