3 Bombay phenotype

The rare individuals with Bombay phenotype do not express H substance on their red blood cells and therefore do not bind A or B antigens. Instead, they produce antibodies to H substance (which is present on all red cells except those of hh phenotype) as well as to both A and B antigens and are therefore compatible only with other hh donors.

Individuals with Bombay phenotype blood groups can only be transfused with blood from other Bombay phenotype individuals. Given that this condition is very rare to begin with, any person with this blood group, who needs an urgent blood transfusion, may be simply out of luck, as it would be quite unlikely that any blood bank would have any in stock.

4 Inheritance

Blood groups are inherited from both parents. The ABO blood type is controlled by a single geneDNA and to a chromosome (right). Introns are regions often found in eukaryote genes which are removed in the splicing process: only the exons encode the protein. This diagram labels a region of only 40 or so bases as a gene. In reality many genes are much with three alleleAn allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. An example is the gene for blossom color in many species of flower a single gene controls the color of the petals, but there may bes: i, A, and B.

A allele gives type A, B gives type B, and i gives type O. A and B are dominant over i, so ii people have type O, AA or Ai have A, BB or Bi have type B. AB people have both phenotypes because A and B express a special dominance relationship: codominance. Thus, it is usually impossible for a type AB parent to have a type O child.

When a type AB parent has a type O child, or when one type A and one type O parent produce a type AB child, it is sometimes mistakenly assumed that the child MUST be illegitimate.

4.1 Inheritance in the Bombay phenotype

Another possible explanation is that the child or parent who tests as type O has the very rare Bombay phenotype: they have inherited two recessiveIn genetics, the term recessive gene refers to an allele that causes a phenotype (visible or detectable characteristic) that is only seen in a homozygous genotype (an organism that has two copies of the same allele). Every person has two copies of every g alleles of the H gene, (their blood group is O_h and their genotype is "hh"), and so do not produce the "H" protein that is the precursor to the "A" and "B" antigens. It then no longer matters whether the A or B enzymes are present or not, as no A or B antigen can be produced since the precursor antigen is not present.

4.2 Rhesus inheritance

Rh is inherited the same way, except that it has two alleles and Rh+ is dominant. Rh Disease occurs when an Rh negative mother who has already had an Rh positive child bears another Rh positive child. The antibodies in the mother's blood react to the infant's blood. This reaction doesn't always occur and is less likely to occur if the child carries either the A or B antigen and the mother does not. In the past, Rh incompatibility could result in stillbirth or death of the mother. Rh incompatibility was until recently the most common cause of long term disability in the United States. At first, this was treated by transfusing the blood of infants who survived. At present, this affliction can be treated with certain anti-Rh(+) antisera, the most common of which is Rhogam.

5 Compatibility

Blood donors and blood recipients must have compatible blood types. O- is the universally compatible blood type. The chart below illustrates how people with different blood types can receive or donate other blood (X means compatible). An A- person, for example, can receive either O- or A-, and can donate to people with AB+, AB-, A+ or A- blood.

Blood compatibility chart

Recipient	Donor
	O-	O+	B-	B+	A-	A+	AB-	AB+
AB+	X	X	X	X	X	X	X	X
AB-	X		X		X		X
A+	X	X			X	X
A-	X				X
B+	X	X	X	X
B-	X		X
O+	X	X
O-	X

6 Frequency

Blood types are not evenly distributed throughout the human population. O+ is the most common, AB- is the rarest. There are also variations in blood-type distribution within human subpopulations.

Type	Frequency
O+	38%
A+	34%
B+	9%
O-	7%
A-	6%
AB+	3%
B-	2%
AB-	1%

7 Other blood types

Other blood type systems exist to describe the presence or absence of other antigens. Diego positive blood is found only among East Asians and Native Americans. MNS systems gives blood types of M, N, and MN. It has use in tests of maternity or paternity. Duffy negative blood gives partial immunity to malaria. The Lutheran system describes a set of 21 antigens. Other systems include Colton, Hh or Bombay, Kell, Kidd, Lewis, Landsteiner-Wiener, P, Yt or Cartwright, XG, Scianna, Dombrock, Chido/Rodgers, Kx, Gerbich, Cromer, Knops, Indian, Ok, Raph, and JMH.

8 Social significance of blood types

In Japan, a popular belief is that personality is related to blood type. From the preponderance of some blood type in a population, "experts" claim to be able to deduce the character of that population. The "experts" also believe that they can calculate how well the blood types of different people match. A Japanese employer could therefore aim to get a proper mix of blood types among their personnel.

Some nationalisms such as the Basque one have used the different proportion of blood types in different regions or populations as a mark of different race.

There are occasional attempts to market fad diet s "customized to blood type."

9 External Reference

• Red Cross Blood Information

Blood

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