Chromosome: Structure and types

 Based on the position of the centromere Metacentric chromosome The metacentric chromosome has its centromere centrally located between the two arms. This gives the chromosome a typical 'V' shape that is seen during the anaphase. The arms of this chromosome are roughly equal in length. Submetacentric chromosome The arms of the submetacentric chromosome are said to be unequal in length. This is because the kinetochore is present in the submedian position. This gives rise to the 'L' shape of the submetacentric chromosome. Telocentric chromosome Also known as the monarchial type of chromosomes, they have a centromere that is located towards the end of the chromosome. Thus, telocentric chromosomes have a 'rod' shaped appearance. Acrocentric chromosome The location of the centromere in the acrocentric chromosome is subterminal (near to telomere). This causes the short arm of the chromosome to become really short making it very difficult to observe. Such chromosome as...

 Chromosome morphology can be well studied at mitotic metaphase. Under the light microscope, the following structural features can be seen: • Chromatid o Chromomere o Chromonema • Centromere • Secondary constriction • Satellite • Telomere • Pellicle and matrix Chromatid Chromatid Chromatid is the structural and functional unit of chromosomes. At metaphase, each chromosome consists of two longitudinal parts called chromatids. These chromatids are held together at a point called the centromere. The chromatids separate from each other during mitotic anaphase (and during anaphase II of meiosis) and move to the opposite poles during anaphase. During telophase and the G, phase of interphase each chromosome is composed of a single chromatid. Since the two chromatids making up a chromosome are produced through replication of a single chromatid during the synthesis (S) phase of interphase, they are referred to as sister chromatids. In contrast, the chromatids of homologous chromosomes are k...

 Strasburger discovered thread-like structures in 1875 which appeared during cell division. The term chromosome was given by Waldeyer in 1888 since these structures showed an affinity for basic dyes and could be stained deeply, while the cytoplasm took little or no stain. The term chromosome is derived from the Greek word 'chroma' which means 'color' and 'soma' which means 'body'. Chromosomes are the organized structures of DNA and proteins found in cells. They are thread-like structures located inside the nucleus of animal and plant cells. Chromosomes are composed of a single molecule of DNA with many copies of five types of histones. Histones are protein molecules and are rich in lysine and arginine residues, they are positively charged. Hence, they bind tightly to the negatively charged phosphates in the DNA sequence. A small number of non-histone proteins are also present, these are mostly transcription factors. Chromosomes play an important role tha...