From haploidy ( ancient Greek ἁπλόος haplóos , simple ') is spoken when the genome in the nucleus of a cell of a eukaryotic present living in a simple form, each of its genes so in only one variant ( allele occurs).
In humans, haploid is typically the set of chromosomes in the nucleus of an egg or sperm . During fertilization , the two haploid chromosome sets of these germ cells together result in twice the chromosome set of the zygote , a diploid cell.
The haploid chromosome set of a human germ cell consists of 23 different chromosomes , 22 of which are autosomes and one is a gonosome (sex chromosome). In the female germ cell, the egg cell, the gonosome is always the X chromosome ; in the male germ cell, the sperm, it is either the X or the Y chromosome . The number of chromosomes can be different in different biological species , including the number n of a haploid chromosome set. The single chromosome set of a haploid cell is given as 1 n , twice that of a diploid cell with 2 n , four times that of a tetraploid with 4 n, etc .; this indicates the degree of ploidy in the nucleus of the cell of an organism. The symbol “x” is used for the basic number of chromosomes in the simple set of chromosomes of a species. In humans, x = 23 indicates the number of chromosomes in the euploid single chromosome set of a haploid cell such as the gamete ; the normal (somatic) cells of his body are diploid (2 n ), so they have 46 chromosomes.
It should be noted that the degree of ploidy in a cell does not necessarily indicate the amount of DNA present . Because chromosomes can exist with two chromatids as well as in the one-chromatid form. For example, both are from the immature germinal cells produced previous male gamete, a secondary spermatocyte , as well as a spermatozoon haploid; so they each have 23 different chromosomes. However, the chromosomes in the spermatocyte are in the two-chromatid form (1 n ; 2c), i.e. with twice the DNA content ( C value ) compared to the one-chromatid chromosomes in the mature spermatozoon (1 n ; 1c) .
- Rudi Balling et al: Textbook of Genetics . Ed .: Wilhelm Seyffert (= spectrum textbook ). 2nd Edition. Spectrum Akademischer Verlag / Gustav Fischer , Heidelberg / Berlin 2003, ISBN 3-8274-1022-3 (1,230 pages, limited preview in Google Book Search [accessed on October 22, 2014] hardcover).
- ^ Luiz Carlos U. Junqueira , José Carneiro : Histology . Ed .: Manfred Gratzl (= Springer textbook ). 6., newly translated, revised. u. act. Edition. Springer Medizin Verlag , Heidelberg 2004, ISBN 3-540-21965-X , chap. 21.1: testicles , p. 373 , doi : 10.1007 / 978-3-662-07780-1 ( limited preview in Google Book Search; [accessed on October 22, 2014] Portuguese: Histología básica . Rio de Janeiro 1995. American title: Basic Histology , New York 2003 / German edition: 479 pages; hardback, including new licensing regulations ;).