A Girl or A Boy?
The birth of a girl or a boy is determined as early as during the child’s conception. During this process the father’s sperm brings with it either an X chromosome or an Y chromosome. If it happens to be an X chromosome, a girl will be conceived and born. If it is an Y one — a boy.
To demonstrate how it works I will take my own example.
The above described process means that during my conception, my father’s sperm brought X chromosome ensuring my creation. At the same time, he delivered Y chromosome to my twin brother. For those who do not know, fathers do not pass X chromosomes to their sons, only mothers do.
The X chromosome that my father passed to me was the one he had gotten from his mother. His father’s chromosome was not passed to him as it is not possible.
Scientists have discovered a mutation near the ADAMTS gene, which is involved in the development of male reproductive cells. The mutation found makes sperm with an X chromosome more active and successful in fertilisation. However, such a mutation is rare — in 0.5% of the 500,000 study participants. So the chances of having a girl is 10% higher if one has the mutation of rs144724107 near the ADAMTS gene.
So, it seems that in my case my father might have had such a mutation, otherwise he would have had a boy.
Now, an intriguing detail. In my X chromosome I have got the rs398122990 (AA) — a haemophilia gene, attributed to so called ‘Royal disease’, transmitted from Queen Victoria (1819–1901) to European royal families. But who has passed it to me — my father or my mother? Before answering this question let’s look at the boys.
The survival of the male embryo is very much affected by his mother’s health. For this reason, in the early stages of pregnancy, male embryos die more often because they are more vulnerable to genetic and external factors.
How is it connected to my example?
During DNA testing with My Heritage I discovered that I have inherited a genome of my unborn twin brother. This became apparent due to presence of information in some of the Y-DNA fields, which first was considered as anomaly. Later, when discussing the matter with a knowledgable person I learnt that my twin brother most likely died before even being born. As he did, his genome got written on to me. His death most likely occurred during early stages of my mother’s pregnancy. This unfortunate event might have been due to my mother’s health state or some other unknown factors.
If my twin brother had survived, he would have inherited my mother’s X chromosome and my father’s Y chromosome. While looking at the DNA results based on the genome of my twin brother, I did not find the rs398122990 (AA) haemophilia gene or any other haemophilia associated genes.
Women inherit two X chromosomes — one from their father and one from their mother. Which one mothers will pass to their child is not known in advance. So, what if my unborn twin brother inherited the X chromosome of my mother without a haemophilia gene. And here comes another intriguing detail. I not only got my unborn twin brother’s genome written onto me, but also my mother’s genome too.
This was discovered during another DNA test which was done with 23andME platform. Checking the DNA field of my mother’s genome I also did not find the rs398122990 (AA) haemophilia gene. This meant that she did not have this gene and therefore could not have passed it either to me or to my unborn twin brother. So, this brought me back to my father and his X chromosome which he inherited from his mother.
Now, my case is rare as not everyone is a carrier of three genomes. To find out what I did would require to have both parents tested. Luckily in my case all that is mine is always with me.
Note: the DNA tests have been done with the following companies — My Heritage (the first test that revealed Y-DNA information); Ancestry (the second test I did that contained the haemophilia gene), and 23andME (the test that revealed the genome of my mother)
