Is the child biological? Uncovering the secret of "hidden genes"

Editor's note: It is common knowledge that children inherit their parents' blood types. However, not everyone will inherit the common blood type, but there are rare blood types. So, what role do genes play in the inheritance of rare blood types? What issues should people with "panda blood" pay attention to? This article will take you to explore the secrets of blood type inheritance.

According to a news report, a strange thing happened in Jiangmen City, Guangdong Province, my country. A father with type O blood and a mother with type A blood gave birth to a baby with type B blood. Such a test result made the parents, who have some knowledge of genetics, very anxious, and they couldn't help asking - is this not my baby?

As we all know, in daily life, blood type can be used as a proof of kinship because it is highly stable in the process of parental inheritance. After the haploid chromosome from the egg combines with the haploid chromosome from the sperm, the offspring will have two blood type determining genes from the mother and father respectively. We usually call a pair of genes located at the same position on the same pair of chromosomes and controlling relative traits alleles. Blood type determining genes are such a pair of alleles.

Blood types are divided into the common ABO blood types according to the different antigens encoded by their genes. People with type O blood can be roughly regarded as carrying two genes, one from each of their parents. People with type A blood and type B blood have genotypes IAi or IAIA and IBi or IBIB respectively; people with type AB blood have genotypes IAIB.

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This is why a baby with type B blood cannot be born from two parents with type A and type O blood, and a baby with type AB blood cannot have two parents with type O blood.

So, did something really go wrong with the family in this news? Is it true that the baby they raised for many years is not their biological child?

In order to thoroughly find out the reason, the parents took the child to the Judicial Center for a paternity test. The results of the paternity test showed that the genetic similarity between the parents and the baby was greater than 99%! This result showed that the baby was indeed born to the couple.

We can't help but ask, if the results of the paternity test and the blood type test are contradictory, then one of them must be wrong, right? But the results of the blood type test again made the parents worried again - the father was type O, the mother was type A, and the child was type B! It was exactly the same as the first blood type test result!

In order to find the answer to this strange phenomenon, the couple, at the suggestion of the staff of the Judicial Office, sent their blood samples to the Blood Transfusion Department of Jiangmen Central Hospital for a more accurate blood type identification.

After a series of more complex and more precise identification experiments, everyone was surprised to find that the key to the problem lies with the baby's mother - her blood type is not type A as previously found, but type AB!

However, this AB blood type is different from the AB blood type we know in general. When we classify blood types in general, we classify people who have both the A antigen-encoding allele and the B antigen-encoding allele as AB blood type. However, the mother in this incident has a pair of alleles that encode both the A antigen and the Bw11 antigen. Since the Bw11 antigen expression is extremely weak, in previous routine examinations, the commonly used test reagents were not potent enough to detect such a weak B antigen expression, and this Bw11 was not detected, causing the mother's blood type to be mistakenly identified as type A.

In the process of chromosome inheritance from mother to child, the chromosome with A antigen gene and the chromosome with Bw11 gene are respectively present in different haploid eggs, and the egg with Bw11 gene is finally fertilized and implanted successfully, giving birth to a new life. Therefore, the baby with Bw11 gene from mother and O gene from father will show B blood type in the blood type test.

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From this point of view, does it mean that routine blood typing tests are unreliable?

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In fact, considering the reagent and labor costs of blood typing, as well as the extremely low proportion of people with A and B blood types in my country, ordinary blood typing reagents do not have the ability to identify very few subtypes. Therefore, ordinary blood typing tests do have the probability of such omissions, but the possibility of such problems is extremely low, and the public does not need to worry too much, nor do they need to distrust blood typing tests.

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According to the basis of blood type distinction in the previous article, we can simply conclude that blood type is distinguished by the antigens encoded by the blood type determining genes on human chromosomes and the corresponding antibodies produced in the serum. So, in addition to the rare blood type typing similar to that in this report, what other rare typings are there in the population? The Rh blood type determined by the Rhesus Factor is the most well-known of these rare blood type typings. In addition, there are Bombay blood that lacks the basic H antigen, P blood type, universal blood type Rhnull, and so on. These are rare blood types found in a very small number of people with the continuous development of scientific and technological means. People who carry the genes of these blood types should pay special attention when receiving blood transfusions and donating blood.

Produced by: Science Popularization China

Author: Wei Yanyu, PhD candidate in clinical medicine at Shanghai Jiao Tong University

Producer: Guangming Science Department of Chinese Society of Agronomy