Inheritance of Blood Types
A child born to parents with the aforementioned blood types may have blood type A, B, AB, or O with a positive rhesus factor. This is because the child’s blood type will be determined by the co-dominant alleles, which are A and B. Notably, alleles refer to genetic information stored in the DNA at a specific chromosome and humans have ABO blood type alleles where A and B are dominant while O is the recessive allele. A child therefore inherits one blood type each from the biological parents (Hosseini, 2007). In this case, a mother with B- and Father with A+ both pass down one of their alleles to the child. First, the father possibly has a combination of AA and AO, while the mother possibly has a combination of BB or BO alleles. According to the law of assortment, each parents’ allele combination is separated equally as meiosis occurs. This simply implies that the child may inherit either AA or AO from the father. Similarly, the child may inherit either BB or BO from the mother (School of Medicine, 2018). When both A and B alleles are inherited along with the O allele, A and B will be equally expressed since they are co-dominant, hence determine the blood type of the child. Nonetheless, the child can only have blood type O if he or she inherits two O alleles from the parents.
Like the alleles, the Rhesus (Rh) factor is genetic information that is independently passed down from the biological parents (Hosseini, 2007). Based on the case above, the mother has a negative rhesus factor (Rh-) while the father has a positive rhesus factor (Rh+). Rh+ genes may have one of possible allele combinations; Rh+/Rh+ or Rh+/Rh- . On the other hand, the mother has a negative rhesus factor and therefore has a one negative allele combination (Rh-/Rh-).
The Rh factor genetic information is also inherited from our parents, but it is inherited independently of the ABO blood type alleles. There are 2 different alleles for the Rh factor known as Rh+ and Rh-. Someone who is “Rh positive” or “Rh+” has at least one Rh+ allele, but could have two (School of Medicine, 2018). Their genotype could be either Rh+/Rh+ or Rh+/Rh-. Someone who Rh- has a genotype of Rh-/Rh-. If the father donates Rh+ while the mother donates Rh -, the child will have a positive rhesus factor. Nonetheless, if the father donates Rh- and the mother Rh-, the child will ultimately have a negative rhesus factor (Rh-).
Since the mother has Rhesus negative alleles, there may arise complications with the child in the case where the child has a positive rhesus factor. This is because the Rhesus factor alleles are stored in the red blood cells and is therefore affected by immune system processes. If the mother’s and child’s blood come into contact through the placenta, the mother’s body will produce antigens to fight the rhesus negative blood cells of the child because it is considered a foreign substance by the mother’s body. When this happens, the mother’s antigens destroy the child’s red blood cells initiating risk for complications like erythroblastosis fetalis, anemia, and jaundice and Hydrops fetalis among others.
Blood types can be used to determine pertanity because a child inherits key genetic markers from his or her father. Scientists therefore use available technologies to identify these markers and determine a 99.99% similarity that either rules out or points the father of a child (Adams, 2018).
Although the O allele is recessive it has a high frequency of expression as opposed to the A and B alleles. Notably, alleles do not appear with equal frequency in the gene pool. The O allele is hence more common as opposed to A and B.
The distribution of blood groups across different ethnic representations is still unclear. However, there exists three common theories used to determine the distribution of blood ratios across populations (Farhud & Yeganeh 2013). The first theory is based on genetic information of monkeys who demonstrated that A, B and O blood groups originated from Europe, Asia and South America respectively. Interracial marriages and other racial mixing factors are attributed to the distribution of these types across the rest of the globe. The second theory follows that all blood groups emerged from mutations of one basic blood group (O), which occurred over millions of years. Old races, like red Indians are therefore considered to have a high frequency of O blood types. The third theory follows that all blood groups emerged from one basic blood type; AB. The emergence of A, B and O blood types are therefore considered a result of genetic mutations that occurred over time. This theory also suggests that O blood type is the most common because it is more resistant to factors like disease.
References
Adams, J. (2018). Paternity Testing: Blood Types and DNA | Learn Science at Scitable. Retrieved from https://www.nature.com/scitable/topicpage/paternity-testing-blood-types-and-dna-374
D FARHUD, D., & Yeganeh, M. Z. (2013). A brief history of human blood groups. Iranian journal of public health, 42(1), 1.
Hosseini Maaf, B. (2007). Genetic characterisation of human ABO blood group variants with a focus on subgroups and hybrid alleles (Vol. 39). Division of Hematology and Transfusion Medicine, Department of Laboratory Medicine, Lund University.
School of Medicine, E. (2018). Retrieved from https://genetics.emory.edu/documents/resources/factsheet43.pdf
