Despite the fact that there appears to be no evolutionary benefit for one blood group over another, their distribution is very unequal. What caused one blood group to become more common than others?
Humans have a variety of blood kinds, or blood groups, which differ based on the types of sugar molecules found on the surface of red blood cells.
Type A blood cells contain sugar molecules of a specific type, whereas Type B blood cells contain sugar molecules of a different type.
Type AB blood cells display both types of sugar molecules on their surface, whereas Type O blood cells do not display either sugar molecule.
The human immune system detects these sugar molecules and treats them as alien elements that must be targeted when they differ from those found in the body on a regular basis. If a person with Type O blood obtains Type A blood, his body will perceive the sugar molecules in Type A blood as foreign, see the donor red blood cells as intruders, and attack them. As a result, it’s critical to match the donor’s blood type to the recipient’s blood type.
Parents pass down their blood types to their children through the ABO gene, which has two copies. The mother gives one and the father the other. The ABO gene contains the instructions for making a protein that attaches one of the sugar molecules listed above to the surface of red blood cells. Alleles, or slightly varied variations of the gene, determine whether the blood is type A, type B, both, or neither.
Blood type O is the most frequent in the population, however, the prevalence of other blood types varies widely. For example, in certain nations, 90% of the population is affected, whereas in others it’s only half of that figure.
Even if two persons have the same blood type, their alleles are not always the same. In a person with type O blood, there could be a variety of reasons why the protein that adds the sugar molecules is inactive. The protein may be too short in one individual, yet it will not function in another due to a structural alteration that renders it useless. There are several variants of blood types A and B, in which the functioning protein creates the appropriate sugar molecule. However, there may be minor changes in the gene that contains the instructions for its creation.
Our genes undergo random mutations throughout generations, which are alterations in the DNA sequence. The majority of the changes are minor, but some can be dangerous, and a small percentage can even be beneficial. If the mutations are deleterious, they are unlikely to spread across the population and will most likely be eliminated by natural selection over time. In contrast, ‘abnormal’ versions of genes that aren’t essential for our existence, such as the ABO gene, can develop and persist in the population. A vast number of different aberrant variants of the gene may emerge as a result of this, all of which will result in type O blood and spread across the population. Although the likelihood of a mutation in the ABO gene being passed down to the next generation is low, the likelihood of a random mutation impairing a working protein and disrupting its activity is higher than the likelihood of a random mutation restoring functionality to a nonfunctional protein. This mechanism may lead to a small increase in the predominance of O alleles over time.
Blood type alleles are passed down from generation to generation, with each person obtaining one from his mother and another from his father, and they might be identical or dissimilar. Because blood type variances do not cause illness, people can pass on their genes whether the ABO protein is active and creates blood types B, A, or AB, or whether it is inactive and produces type O blood. As a result, there is no evolutionary pressure for a particular gene variant to become dominant in the population. Instead, there’s random drift, or random variations along the gene that could lead to a situation where one allele is more widespread in the population over time.
This is a likely scenario for those who have type O blood, which has become the most prevalent type in the human population. It takes the shape of modest, random alterations that eventually lead to a certain result, such as rolling dice, which will almost certainly produce a different number each time.
Some diseases may affect people with Type O blood significantly more than others, which could explain the higher incidence of Type O blood amongst the general population. Malaria is one example of this, in which the parasite that causes the sickness manifests itself in a lesser form in persons with type O blood. Studies have found a statistical association between blood type and the probability of contracting a specific disease, but they haven’t proven that the two factors are causally linked, nor have they proposed a mechanism that would relate disease prevalence to blood type.
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