See also: sex determination
Biological bases
Each cell of the human body, except the sexual ones, contains 23 pairs of chromosomes; of these, 22 contain information for the development of the body, while the twenty-third pair contains the gene sequences for the development of internal and external sexual organs. These two sex chromosomes, designated by the letters X or Y, are therefore decisive for the sex of the individual. In a female, this pair consists of two relatively large chromosomes, called X, while in the male we find an X chromosome flanked by another, much smaller and asymmetrical, called Y.
The sex cells or gametes (ovum in the female and sperm in humans) possess only half of the chromosomal outfit, therefore 23 single chromosomes, due to the meiotic division that occurs during their formation. Thanks to this division, when the egg and the sperm join together, the resulting cell, called zygote, contains a complete set of 46 chromosomes (23 pairs). During gamete reproduction, the distribution of the individual chromosomes is CASUAL: the mother, being endowed with the XX pair, will always transmit the X chromosome, while the father (XY) will produce spermatozoa Y and spermatozoa X.
SUMMARY: each female somatic cell (all cells in the body except the sexual ones) contains 2 X chromosomes, while each female gamete (ovum) contains only one.
In the father, all the somatic cells are characterized by an X chromosome and a Y chromosome, while the sex cells can contain either an X chromosome or a Y chromosome:
When an egg, with its X chromosome, merges with a spermatozoon with the Y chromosome, a male will come to light; when instead an egg melts with a spermatozoon containing another X chromosome, the unborn child will be female.
In other words, during conception the presence or absence of the Y chromosome in the paternal spermatozoon determines whether the fetal development will proceed, respectively, towards the male or female line. The sex of the unborn child therefore depends exclusively on the genetic contribution of the father.
Curiosity
Scientific research has revealed some differences between spermatozoa Y and X; the first (masculine) would be smaller and faster, but not very resistant, while the second (feminine) would be slower, but stronger and longer-lived.
Based on this premise, some measures could offer a greater probability of conceiving a child of a particular sex. In particular, to favor the conception of a boy, it would be useful:
- consume close sexual relations between them;
- concentrate sexual intercourse on the day of ovulation;
- during intercourse, adopt a position that involves deep penetration.
Conversely, the conception of a sissy would be favored by:
- consume infrequent sexual relationships;
- consume sexual intercourse in the pre-ovulatory period;
- adopt a position that involves a shallow penetration during intercourse.
Although based on a scientific assumption, these techniques lack scientific confirmation regarding the real effectiveness.
Clinical Applications
Thanks to the differences related to their specific genetic heritage, it is possible to biochemically separate the Y sperm from the X ones. This voluntary determination of sex, which raises ethical problems of no small importance, has very important repercussions in situations where one is aware of genetic diseases linked to sex in one's family.
A mother suffering from color blindness or hemophilia, for example, will have a 50% chance of generating a sick male, while female daughters will be healthy or at most healthy carriers of the disease (if the father is healthy). On the contrary, when a male with these pathologies has children, no male child will be affected, while all the daughters will be carriers (if the mother is healthy). Haemophilia and color blindness are in fact two hereditary diseases linked to sex chromosome X.
