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Con il nome di cromosoma 21 si indica per convenzione il più piccolo cromosoma umano in ordine di grandezza, con circa 47 milioni di nucleotidi. Gli individui presentano solitamente due copie del cromosoma 21, come di ogni autosoma, che rappresentano circa l'1,5% del DNA totale nella cellula.
Chromosome 21 is one of the 23 pairs of chromosomes in humans. Chromosome 21 is both the smallest human autosome and chromosome, with 45 million base pairs (the building material of DNA) representing about 1.5 percent of the total DNA in cells.
La sindrome di Down, più propriamente trisomia 21 e, in passato, mongolismo o mongoloidismo, è una condizione cromosomica causata dalla presenza di una terza copia (o una sua parte) del cromosoma 21. Viene anche abbreviata DS dall'acronimo del suo nome in inglese, Down syndrome.
Chromosome 21 (Spanish: Cromosoma 21) is a Chilean crime thriller television series co-created by Matías Venables and Nico Martínez Bergen. The series traces a police investigation into a young man with down syndrome involved in a murder.
Down syndrome (also known by the karyotype 47,XX,+21 for females and 47,XY,+21 for males) is mostly caused by a failure of the 21st chromosome to separate during egg or sperm development, known as nondisjunction.
A chromosome is a package of DNA with part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome -forming packaging proteins; in eukaryotic cells the most important of these proteins are the histones.
The trisomy 21 karyotype figure shows the chromosomal arrangement, with the prominent extra chromosome 21. Trisomy 21 is the cause of approximately 95% of observed Down syndrome, with 88% coming from nondisjunction in the maternal gamete and 8% coming from nondisjunction in the paternal gamete.
