Haploid

A biological cell is haploid (of the Greek aploos , simple and eidos , in form of) when the Chromosome S which it contains are each one in only one exemplary ( N chromosomes). the concept is generally to oppose to Diploïde, term indicating the cells with chromosomes in double specimen ( 2n chromosomes) .

An organization or part of organization is known as haploid when its cells are themselves haploid.

These definitions relate to only the organizations Eucaryotes (Protistes, Animaux, Végétaux, Champignons), which have truths chromosomes. It thus excludes for example the Bactérie S which do not have a core and have chromosomes of a particular type.

The reproduction sexuée which implies a genetic exchange brings into play mechanisms of reduction (Méiose) and of increase (Fécondation) in the repetition of the chromosomes (Ploïdie). The life cycle of an organization eucaryote thus includes/understands necessarily an alternation of stages with different levels of chromosomal repetition: one speaks about alternation of phase (see Life cycle (biology)).

At the human ones, and the majority of the animals, the haploid phase ( N ) are very reduced. It corresponds to the formation of the Gamète S: Spermatozoon or Ovule. The organization (the body) develops in phase Diploïde ( 2n ): the cells contain each one the chromosomes in double specimen.

At the foams, at some Alga S, the developed vegetative part of the organization corresponds to the haploid phase ( N ). The phase Diploïde ( 2n ) on the contrary is limited much, restricted to the zygote.

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