By Noelle Darts
WORD BANK
Hair color, eye color, sex, height, blood type; these observable characteristics (phenotypes) are created by proteins and RNA which are synthesized by genes in one's genotype. Blood type is one of the most important genetic characteristics and its three defining alleles were discovered by Karl Landsteiner in the early 20th century; Landsteiner’s discovery has been hugely influential by both influencing safer practice in blood transfusions and by fueling the field of hematology. This scientific article will further explain the importance of blood, how blood alleles determine your given phenotype, how to find out your probable blood type based on your paternal alleles and how blood types greatly influence medicine and their importance in ensuring safe blood transfusions in order to save millions of lives per year.
Blood has many uses; the human body contains on average around 5,000 cm3 of blood which can be used for the transportation of oxygen and nutrients, filtration, the formation of blood clots, fighting infection and regulating body temperature amongst many other uses that are mandatory for human function. This is why blood types, drives and transfusions are so important; everyday, over 30,000 pints of blood are used in the United States and donations, which rely on the knowledge of blood types, are needed every three seconds.
Amongst humans, there are four different blood types: A, B, AB, and O, which stem from three different alleles: A, B, and O. The alleles A and B are dominant whilst allele O is recessive, meaning that if one genotype is e.g. AO only the A blood type will be expressed. If one genotype is AB, as both are dominant, the blood type will be expressed as AB. An important aspect in maintaining genetic variation in a population is the ability for the genotype of the offspring from two parents to potentially differ from that of both parents due to random cell division in meiosis and the combination of random gametes in fertilization to create a new organism with an original genome. If the alleles of the parents are known, this information can then be used to calculate the probable blood type of the offspring.
Here’s an example of a Punnet square that could be used to calculate the offspring’s possible blood types if parent 1 has blood type AB and parent 2 has blood type B with an unexpressed O allele:
(The letters in bold are the dominant alleles and therefore the phenotypes expressed)
As you can see, 2/4 of the phenotypes are blood type B while ¼ are A and ¼ are AB.
It can be predicted that the offspring will have a 50% chance of having blood type B, a 25% chance of having blood type AB and a 25% chance of having blood type A.
Blood types are classified by both the existence or lack of the A antigen and the B antigen, found in red blood cells, and the existence or lack of the A and B antibody, found in the plasma. Blood type A contains the A antigen and B antibody, type B contains the B antigen and A antibody, type AB contains both A and B antigens but neither antibodies and type O has no antigens but both antibodies. This information is very useful in determining which blood types can be donated and which types can be received, as, if the body detects foreign antigens it will try to ‘terminate them’ which can lead to kidney failure and eventually death. Blood type O is known as the universal donor as it can be donated to any blood type as it contains no foreign antigens for the body to attack. However, if blood type B, which contains B antigens, were to be donated to someone with blood type O the body would produce an immune attack to the transfused blood; this is why it is vital that blood type is tested, known and donated.
Blood is not only classified by the A and B antigens and antibodies but is also classified by the presence or lack of the Rh (rhesus) protein, a protein found on red blood cells. Like blood types, the Rh factor is genetically inherited and is specifically important to be aware of to ensure the safety of fetuses; if a Rh-negative woman is pregnant with a Rh-positive fetus, the woman may produce Rh antibodies when the blood mixes during delivery which, if she becomes pregnant again, may attack the second fetus’ red blood cells which can lead to the fetus developing anemia or dying. The Rh factor can also affect first born children if the mother is exposed to Rh-positive blood in a blood transfusion; this would cause the mother to produce Rh antibodies which could then be passed on to her child.
To conclude, blood is a necessary part of the human body and ensures multiple bodily processes, such as the transportation of oxygen and nutrients and the formation of blood clots. It is inherited from a mixture of paternal genotypes and can be placed into four groups based on the existence or lack of A and B antigens and antibodies and can be classified as positive or negative based on the existence of the rhesus protein. It is clear that Landsteiner’s discovery of blood types and the Rh protein has saved millions of lives by making blood transfusions a safe and reliable practice and has forever changed the course of medicine.
Citations:
Dean L. Blood Groups and Red Cell Antigens. Bethesda (MD): National Center for Biotechnology Information (US); 2005. Chapter 5, The ABO blood group. Available from: https://www.ncbi.nlm.nih.gov/books/NBK2267/
Desjardins, L., Blajchman, M. A., Chintu, C., Gent, M., & Zipursky, A. (1979). The spectrum of ABO hemolytic disease of the newborn infant. The Journal of Pediatrics, 95(3), 447–449. doi:10.1016/s0022-3476(79)80533-8
Landsteiner, Karl. “Uber Agglutinationserscheinungen Normalen Menschlichen Blutes.” Wiener Klinische Wochenschrift, 1901, pp. 1132–1134.
Edited by: Simoni Shah and Ashna Chaturvedi
Comments