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Fenotipic determination. In many species, dotacón genetic does not determine the type of sex totally, and are the environmental conditions those that make this determination. Many superior plants that produce hermafroditas flowers can masculinizar or feminizar their flowers when fitohormona is dealt with some.
In some marine worms of the Poliquetos class, the individuals jsvenes are all males and the adults all females. In addition when several females grow together in a closed atmosphere, but the young ones end up transforming itself into males, by one influence ectohormona elaborated by mature ova.
In species of frogs and toads, the males are hermafroditas in their youthful phase and the adult females can even happen to hermafroditas and to males. In temp Frog, the larvae geniticamente females that are developed to 28: Cs give rise to males and the genetically male larvae, and the genetically male larvae that are developed less than 10: Cs, give rise to females. Genic determination. In some species the sexual determination is produced by a gene with several alelos. It is the case of the gherkin of the devil, in which three alelos for the sexuality occur. Chromosomic determination. The case commonest of sexual determination is that in which the genes that determine the sexuality meet in certain chromosomes that are called sexual chromosomes. In all the cells of an individual, except in the gametos, two series of chromosomes exist, that form pairs of homologous, that is to say, their chromosomic dowry, that we represented by 2n.

When grouping these pairs of homologous exist a pair of chromosomes that is different according to we are studying a female or a male.
Inheritance and sex. These two chromosomes that can be identified by their form and tamaqo, like pertaining to one of both sexes, denominate sexual chromosomes, whereas the even rest of homologous chromosomes, that is equal in size and forms for both sexes of a same species, denominate autosomas. The graphical representation of all the chromosomes of an individual as far as the number, size and form constitutes the CARIOTIPO. The sexual chromosomes have denominated X and and. In the mammals, the cells of the male individuals contain a bread XY and the cells of the females by a pair XX. In the human species, whose chromosomic dowry is of 46 chromosomes, each somatic cell contains 22 pairs of autosomas but a pair XX if it is a woman and 22 pairs of autosomas and a pair XY if it is a man.

The sexual determination is noticeable at the moment of the fertilization and comes fixed by the type from gametos that are united. The women only produciran a type of svulo with 22 autosomas and a sexual chromosome X, whereas the men formed two types of spermatozoa, 50% carriers of a chromosome X and 50% carriers of a chromosome and. To the being the fertilization product of the chance, I ovulate can be united to anyone of the types of spermatozoa that have taken place, reason why in half of the cases females formed and in another 50% males formed.

Cariotipic Determination. In Himenópteros social (bees, wasps…) sex comes determined by the chromosomic dowry: the diploides individuals are females and the haploides are male.