L2 - Karyotype

• Histones 


  • Five small basic proteins (H1, H2A, H2B, H3 and H4) in nucleus of eukaryotic cells
  • Forms molecular complexes around which DNA winds
• Octameter 


  • A complex of eight proteins found at the center of nucleosome (basic structural unit of DNA packaging in eukaryotes)
  • Consists of 2 copies of each of the 4 core histone proteins (H2A, H2B, H3, H4)
• Nucleosome 


  • a basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA that is wrapped around a core of histone proteins.
• Linker DNA 


  double-stranded DNA between two nucleosome cores. Associates with histone H1 and holds the cores together.

  
• Chromatid


  one copy of a newly copied chromosome which is still joined to the original chromosome by a single centromere.

  
• Centromere


  a specialized structure on the chromosome, appearing during cell division as the constricted central region where the two chromatids are held together and form an X shape
• Telomere


  a region of highly repetitive DNA at the end of linear chromosomes.
• Kinetochore 


  a disc-shaped protein structure, found at the centromere of a chromatid, to which microtubules attach during cell division

  
• Euchromatin


  low compaction level of interphase chromosomes, transcriptionally active.

  
• Heterochromatin


  tightly compacted regions of chromosomes, transcriptionally inactive (in general). Exists in two types - constitutive and facultative.

  
• Barr-body (sex-chromatin)


  the inactivated X chromosome, observed as a dark-stained spot at the periphery of the interphase nucleus of each female somatic cell.

  
  

  In each cell the number of Barr-bodies is equal to the number of X-chromosomes-1, i.e. (nX-1)

  
• Karyotype


   the number and appearance of chromosomes in the nucleus of an eukaryotic cell (the qualitative and quantitative characteristic of the chromosomal set of an eukaryotic species).