akrosentriset

Akrosentriset refers to a class of chromosomes whose centromere is located near one end, producing a very short p arm and a longer q arm. This arrangement gives the chromosome an asymmetric, “tip-oriented” shape compared with metacentric or submetacentric chromosomes. The short arm is typically small and rich in repetitive DNA, including nucleolar organizer regions that contain ribosomal RNA gene repeats; the long arm carries the majority of the genetic material and most genes.

In humans, five chromosome pairs are acrocentric: 13, 14, 15, 21 and 22. The short arms of these chromosomes often contain satellite DNA and are largely noncoding; the nucleolar organizer regions on the p arms are the sites of ribosomal RNA gene activity. Because the p arms are repetitive and nonessential in many contexts, acrocentric chromosomes are notable for their involvement in Robertsonian translocations, events in which two acrocentric chromosomes fuse at the centromere to form a single chromosome. Such rearrangements can reduce the chromosome count and, when involving chromosome 21, can contribute to Down syndrome.

Akrosentriset is a term used in cytogenetics to distinguish these chromosomes from metacentric and submetacentric types, where the centromere sits more centrally along the chromosome. The concept is relevant for karyotype analysis, evolutionary biology, and clinical genetics, where variations in acrocentric chromosomes can have diagnostic and reproductive implications.