Video Transcript
A sample of red blood cells is
taken from a person. The blood cells are found to have
type A antigens on their cell surface, and there are anti-B antibodies in the blood
plasma. Which blood group does this person
belong to?
There are four blood types: A, B,
AB, and O. The four blood types are an example
of a trait in humans that is controlled by a person’s genetics. There are three corresponding
alleles, or variants of genes, that can combine to make these blood types: A, B, and
O alleles, written as a superscript over an “I,” as shown in the second column of
this table. Two IA alleles or an IA and an IO
allele will result in type A blood. Two IB alleles or an IB and an IO
allele will result in type B blood. An IA and an IB allele will result
in type AB blood. Two IO alleles will result in type
O blood.
IA alleles code for A antigens,
which are proteins found on the surface of red blood cells. IB alleles code for B antigens,
which are different to A antigens. IO alleles don’t code for any
antigens. Therefore, someone with the blood
type AB will have both A and B antigens on their red blood cells, while someone with
blood type O won’t have any. Antibodies are proteins your immune
system makes in response to the presence of foreign antigens. Antibodies are able to bind to
complementary antigens. Depending on someone’s blood type,
their blood may naturally contain anti-A antibodies that can bind to the A antigen
and trigger an immune response, anti-B antibodies that can bind to the B antigen,
both, or neither.
As they are meant to help against
foreign substances, an individual will usually only produce antibodies for antigens
they don’t have. For example, someone with type B
blood will have anti-A antibodies but not anti-B antibodies.
Now we have enough information to
answer this question. If someone has type A antigens on
the surface of their red blood cells and anti-B antibodies in their blood plasma,
they most likely have blood type A.
