The floor is a set of signs by which organisms with the ability to sexual reproduction, divided into male and female.
The concept of gender, originally formed on the basis of observations of the higher animals, gradually spread to the lower forms.
At different steps of evolutionary ladder you can find different stages of differentiation of the sexes: many-celled animals the same cell can be the cell body and sex; multicellular is a specialization of some cells develop in the male sex (sperm)and some women (eggs). Organisms that produce both groups of reproductive cells (see), are hermaphrodites.
The separation of the sexes (see Sexual characteristics) has implications for the evolution of organisms, providing a wider variability (see), so when fertilization occurs mixture of hereditary traits parental organisms (see Heredity).

Floor - belonging organisms and produced their special cells to one of two groups that differ from one another fact that representatives of one group have sexual process with representatives of the other group. If the sex cells (see) same sex larger and less mobile than the cells of the other sex, the sexual process between them is called anisogamy. If the sex cells do not differ externally, the sexual process is called izogama. Cells are larger and less mobile or stationary called the women, and the small and agile, male. If the sex cells outwardly indistinguishable, cells of the same sex denote a + , and the cells of a different sign. If the body produces cells of both P., it is designated as monoecious, and if it produces only one type of germ cells, it is referred to as dadanet. Dioecious organisms bisexual, i.e., the female body is hidden carries the genes of the male P., and the male - female genes P. In this case, we are convinced cases of hermaphroditism (see), when under the influence of those or other reasons, the body begins to show signs of another P.
If Razdolnoye manifestation of a floor at this organism may depend on the environment (phenotypic definition P.) or hereditary factors (genotype determination P.). Genes that suppress the manifestation of one of the P. and promote the display of signs P. another, called implementers P. In some species of animals and plants implementors P. weak, and their effect is easily suppressed various external influences. Such organisms are called poluvagonami (these include, for example, animal - frog, from plants - hemp); these species under the influence of environmental influences is often observed hermaphroditism.
All mammals animals, including humans, is genotypic definition P., and sex is determined at the moment of fertilization (see). Women have in the cells of the body and 22 pairs of autosomes and one pair of the same sex chromosomes, called X-chromosome. Every egg cell (see) women has 22 autosomes and one X-chromosome. Spermin men also contain 22 autosomes, but half of them contains the X chromosome and the other half of the Y-chromosome. If the egg is fertilized by sperm from the X-chromosome, it develops a woman. If it is fertilized by the sperm with the Y-chromosome, that is developing the man, whose body cells 22 pairs of autosomes, one X chromosome and one Y chromosome.
This type of sex determination referred to as XX-XY; female P. in this case, homogametic and the men of heterogametic. This same type of definition P. there are many insects and most of flowering plants. Birds and butterflies relations reverse, i.e. the female gender of heterogametic (sex chromosomes are indicated here ZW), and the male point of homogametic (ZZ). Sex chromosomes differ from autosomes fact that they are more intensively painted some histological paints and when nuclear fission (see Meiosis) dismissing them to different poles delayed relative to the autosomes. Women have one X-chromosome stronger colored paints than the other, and, as research has shown, most genes in the chromosome is inactive.
The woman, heterozygous in respect of the gene, located in the X-chromosome is a mosaic in respect of this gene. Gene muscular dystrophy, for example, localized in the X-chromosome. If a woman heterozygote in respect of this gene, some cells of the muscles normal, since these functions X chromosome with a normal gene, and other defective, because it offers the chromosome gene dystrophy. It's been proven muscle biopsy heterozygous females. A matter of chance,in which the cell what X chromosome will become inactive. It is defined in the beginning of the development of the zygote stage 32 cells, then the nature of X-chromosomes is stored in the offspring of these cells throughout embryonic development. In non-fissile nuclei, with appropriate color of inactive X chromosome is visible near the shell of the nucleus as little more intensely colored ball, called sex chromatin. The presence of sex chromatin female cells can be distinguished from men like germs (before the floor they found another way)and in different cells of the body. Thus, women in a cell in the body is fully operational only one X-chromosome; as for the second X chromosome, the functioning remains only a small part.
In cultures of cells or pieces of skin, obtained by biopsy, it is easy to analyze chromosomes of a living person. This method has found that people frequently observed various deviations from normal set of chromosomes (see), dependent on both of those or other anomalies during fertilization of the egg, and violations of the processes of fission of nucleus (see Hereditary diseases). There are people who have the formula HO, i.e. which have only one X chromosome. It is women that detect some anomalies known as Turner syndrome; they often fruitless. People with formula XXY or XXXY - men having some anomalies (syndrome Klinefelter). Some animals relationship between X - and Y-chromosome can beat others. In Drosophila formula HO determines the development of the male sex.
As the added with the X chromosome and a Y-chromosome are in the ratio 1:1, it would be expected that the ratio between the sexes will also be 1:1. In reality, the person that attitude is never observed. The number of conceptions boys much more than the number of conceptions girls (primary relationship between P.). At the birth of boys slightly more than girls (secondary relationship between P.), and finally to sexual maturity, the number of men is a bit less than women (tertiary relationship between P.). The reason that boys at conception more than girls, not sure. Maybe here plays the role of the competitiveness of the sperm with the Y-chromosome in comparison with sperm from the X-chromosome in the fertilization process.
The development of sexual characteristics (see), after the embryo differentiate the sex glands and throughout later life, is under the control of sex hormones (see). At present, the mechanism of action of hormones deeper studied at the molecular level. Sex hormones act on certain parts of chromosomes tissue, encouraging people to the activity of these sites (RNA synthesis and protein synthesis). Here there are processes, referred to as feedback: genes determine the development of the endocrine glands, secretion of these glands in turn affects the genes.