The Y

We all know human cells have 23 pairs of chromosomes.Now, when a new cell is created by fertilisation of the egg cell and sperm cell each of them donate the full complement of the chromosomal footprint. generally speaking, you get a pair of genes that have similar functionality. Say, for example one certain gene dictates the color of your eyes. Also further assume one of the genes is defective, then the body uses the backup gene and gives it the color of the eye dictated by it. Either way, the idea is that one can fail, the other contributes (if both are defective, then it is a manufacturing problem that we cannot attend to albeit the complexity of the cell biology does try to make up for it as best as it can but this happens rarely where both genes fail)

The critical part is in the 23rd chromosome as the above logic cleanly applies to 22 pairs as the 23rd one is a li'l bit different. As you know men have XY chromosome pair and women have XX pair as the 23rd one.The Y chromosome is special in that it does not contain any genes, it is simply a stub (most programmers do understand stubs versus full bodied functions). A stub is like an empty container that can be filled in as the structure of the container permits. This means that male sperm cells are gonna be a wee bit lighter than female egg cells (two Xs for 1 X and small stub..this also means there's slightly greater than 50% chance that the offspring would be male than female because Y gets to the other female X faster than the normal male X).

Since Y doesnt have a gene, there's no chance of any defect happening, so the only case that can go wrong here is the X chromosme's gene. Assuming the defective X is fertilized by a Y which results in a boy (for XY means it has to be a boy) who would be defective in some characterstic.Note this point.

On the other hand, you might have the defective X fertilized by normal X which means you have a girl who has a 50-50 chance that she will have a defect. This means that if you have 4 dauthers all 4 of them will have a defect or none of them will (thats why 50-50 in the manifestation sense and not neccesarily 2 girls having the defective gene and 2 girls not). What happens to such a girl? Since one X is defective the other X would take care and nothing happens really for the defect to be expressed in her lifetime and everything would be normal for her. However, she is a "carrier".

Well, from all this if you conclude that a mother who has no defects can produce daughters where all of them have this defect or none of them and only sons seem to be affected, you are not to blame (I thought the same).

However, the lesson is subtle which can be summarized thus: In such 23rd pair interactions, a male may show a defect but will not have defective children whereas a female who doesnt show a defect can have defective children. Females are carriers and Males terminators.Chew on that.

In future, based on much more complicated analyses than this example,I expect a system of genetic matches (much like our current day horoscope matches) before anybody gets into wedlock. After all, your childrens' future can be greatly influenced by deciding whom you marry