Material of Chromosome
Chromatin is the basic material of chromosome. Chromatin can be of two types depending on staining properties. These are listed below..
- Euchromatin are portions of chromosome with lightly packed DNA, partially condensed and stain lightly. DNA is packed in 3 to 8nm fibers.
- Genes situated on this portion are structural genes, these genes undergo replication and participates in the active transcription.
- Most of this chromatin disperse after completion of mitosis.
- Euchromatin comprises the genetically most active portion of the genome, have role in phenotypic expression of genes.
- Heterochromatin are the portions of chromosome with tightly packed DNA, always remains in the condensed state and stain dark. DNA is tightly packed in the 30nm fibers.
- Definition by Heitz: those regions of the chromosome that remains condensed during interphase and early prophase and form so called chromocentre.
- Late replication
- Limted transcription
- Have high content of repetitive DNA sequence.
- Contain very few structural genes.
Types of Heterochromatin
There are two types of heterochromatin viz. Constitutive and facultative heterochromatin.
- Constitutive heterochromatin – DNA of this type of chromatin is permanently inactive. It remains in condensed state throughout the cell cycle, never transcribed. Most of the chromatin occurring around centromere, in the telomers, in c-bands of chromosome is constitutive heterochromatin.
- Facultative heterochromatin – No permanent condensation, follow periodic dispersal. While in dispersed state, it is actively transcribed.
Types of chromosome are given on the basis of number of centromeres and position of centromere.
Structure of Chromosome, especially of eukaryotic chromosome is explained on this page. Visit to know more.