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What my son taught me about my genes

My two children: Akash (left) and Aman(right)

They are my two sons: Aman and Akash. When Prabha was discharged from the hospital after the delivery, she and I were given the blood reports of our two sons. Their blood reports told me something about my own DNA. In this post, I am going to explain what I learnt and how. Knowing that needs an understanding of what dominant and recessive genes are. So here are the basics.

All our DNA resides in strands called chromosomes. You can think of them as long strips holding our genes. Different genes reside on different chromosomes, and we need 23 of them to build a complete body. But all our cells (except for sperms and eggs) contain not 23 chromosomes, but 23 pairs of chromosomes. We get one set from the mother and one set from the father. Every cell provides two plans of building a body. But then, as we all know from personal experience, only one body is built. How is the choice made?

Consider for example the colour of your eyeballs, and assume that this depends on only one gene (this is hypothetical and need not be true, as some traits depend on multiple genes). Now if your mother gave you a gene for a brown eye colour and the father gave you a gene for a black one, which colour will be yours? That depends on the type of genes.If the gene for a brown colour is a dominant gene, then that will get precedence over the other gene and you will end up with a brown eye . In such a case the gene for the black eye is called recessive, because, the only way for you to have a black eye is if both parents give the black eye gene to you, so that the black is not dominated by the brown gene.

Similarly, our blood groups too are determined by the two genes we get from our parents. The commonly used blood group system is called the ABO system*. In this there are 4 blood groups: A, B, AB, O. Any person will belong to one of these types. This is determined based on what genes your parents gave you. To explain that, see the picture below which gives the different types of blood groups that a child can have for the different combinations of genes that the parents can give.

Blood group type that a child’s blood will belong to, for different combinations of genes received from parents.

The yellow boxes are the easy ones. Both mother and father have given the same gene, and so the child also has the same blood group. But if one parent gives an A/B and another parent gives an O, what happens is that the A or B overrides O (the green cells). This means the gene for A blood type is dominant to O. Similarly B is also dominant to O. If one parent gives A and another gives B gene, then the child’s type is AB (the blue cells). This is another way in which genes can interact. One need not always be dominant over another. They can be co-dominant. And this is what happens in AB. Both the A gene and the B gene are expressed. Here is a picture from Wikipedia explaining the same thing.

Blood group inheritance

Now that we have learnt the fundamentals, let us get on with the meat of my post. My wife’s blood group is O, which means, as you can see from the table above, she has two O genes. So, she is capable of giving only O gene to her children. My blood group is A, but that does not help me determine whether I am an A, because both of my chromosomes have A gene (let us call it AA possibility), or if it is because I have an A and an O, and I am an A because of the dominance (let us call this AO). This, I dont know.

I mean, I did not know. But my sons’ blood reports have solved this for me. One of my sons, Aman, has a blood group of O, and the other son Akash has a blood group of A. Both of of them would have received one gene each from Prabha and me. Prabha has definitely given an O to them, as I explained in the last paragraph. What I could have given them is not clear. Since Akash has an A, and Prabha cannot give that, it came from me. But this still does not tell me whether I am an AA or an AO. But Aman has got a blood group of O, which means I too, in addition to Prabha, must have given an O (refer to the table above. Only if both DNA strands have an O gene, will the blood group be O). Which means, I too must have had an O. That I have an A gene, is obvious becaues my blood group is A. But Aman has confirnmed that I have an O too. I have genes for both A and O in my genome. Elementary.

A final point before we close. Note that, if I had two A genes, I can never deduce that from the blood group of my children. Because even if both my sons were of A group, it is possible that I still have an O, but gave only A to both my sons. So the only way to confirm an AA would be to study my genome. Another option could be for me and Prabha to have as many children as we can have in our lifetime, and do a statistical analysis based on a 50% probability of my giving an A or an O to my children. But even that would still be subject to a very small chance of error (Just in case you are wondering, No, we are not planning to do that).

As every parent possibly does, I too have some wild ambitions (I would not want to dignify those thoughts with the word “plan”) on how and what I want my children to learn. But to my complete surprise, within a week of their birth, they taught me something about myself. There sure lie interesting times ahead.

_____________________________

* – While writing this post, I learnt that this ABO system is just one of more than 30 systems in which blood groups can be classified.

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  1. January 29, 2013 at 20:27

    To test for associations between severity of lung disease, key clinical phenotypes, and polymorphisms in ABH genotypes, Fisher’s exact test was used. All tests were two-sided. To investigate the effect of blood group alleles (ABO genotype, nonsecretor phenotype, and FUT3 genotypes producing Lewis negative phenotypes) on CF lung severity risk, we performed multiple logistic regression analyses to predict severity status. The number of A and B antigen alleles was included in an additive model on the log-odds of severe lung status, as well as the FUT2 and FUT3 genotypes, and terms to account for possible interaction between the genes. In addition, the following predictors were used in the model: gender, meconium ileus, asthma, and the TGFb1 codon 10 CC genotype (previously shown to be associated with severe lung disease.) In order to determine whether ABH type influenced the age of acquisition of P. aeruginosa, Kaplan-Meier analysis was performed using SigmaStat® software. ABO type, and secretor and Lewis status were evaluated in the mild versus severe groups. Additionally, to address the possibility of age confounding the analysis of P. aeruginosa acquisition, ABH types were also analyzed in the severe group versus the group of mild patients who were aged 15–28 years (“young milds,”) and interactions among the three ABH types were analyzed. Allelic comparison that yielded a statistical significance of ≤0.05 was considered significant. Unadjusted p-values are reported.

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