When a couple decides to have a child they are uncertain what the child will look liike, what sort of personality the child will have, or even whether the child will have inherited genetic defects. The biggest reason for this uncertainty is that each person donates half of their genetic complement to their children but they do not control which half they donate.
The human genome is made up of 23 pairs of chromosomes. One of each pair came from the mother and the other came from the father. Lets call each member of each pair A and B where the A chromosomes are from your mother and the B chromosomes are from your father. So you have chromosome pair 1 and it has members 1A and 1B (1A from your mother and 1B from your father) and the same for the other pairs, 2A and 2B, 3A and 3B, and so on. Well, when you have a child you could donate all your A chromosomes or all your B. Or you could also donate all your B chromosomes. But you could also donate just 1 of your As with 22 Bs or 2 of your As with 21 Bs. So how many possibility combinations can you donate? The number is is 2 to the 23rd power or 8,388,608 unique combinations.
Well, it still takes two people to produce a child and your mate can also donate just as many different combinations. The total possible combinations of genetically distinct children you can have from different chromosome pairings is 8,388,608 times 8,388,608. That's 2 to the 46th power or over 7 to the 13th power or over 70 trillion combinations. This is why two children of the same parents can be so different from each other. In fact, while it is extremely unlikely to happen it is possible for two siblings to have no chromosomes in common. For instance, one sibling could get the A chromosomes of each parent and the other could get the B chromosomes of each parent.
Right now it is difficult and expensive to control which chromosomes get passed along and it is only practical for a single chromosome and only then in extreme cases. Typically it is done to assure that a child will not carry some genetic defect that each parent possesses or to make the child genetically compatible with an existing child which needs a cell donor to treat a genetic disease.
Since the meaning of most genetic differences is not understood at all even if we today had the ability to control which of each chromosome pair we wanted to pass along we wouldn't have any reason to try. We simply don't know enough to choose one chromosome over another except in rather exceptional situations.
So how will control of which chromosomes get passed to offspring affect mate choice? Well, this will be good news for some men who might otherwise be passed over when females are selecting mates.
|Share |||Randall Parker, 2002 October 01 04:37 PM Biotech Reproduction|