MAKEUP

 Architecture of Chromosome

Chromosome, the microscopic threadlike part of the
cell that carries hereditary information in the form of
genes.
 Chromosome= chroma (colour) + some (body)
 In 1842, Karl Wilhelm von Nageli, a swiss botanist
first observed the rod-like structure present in the
nucleus of the plant cell.
 Chromosomes were first discovered by Strasburger
in 1815 .

Walter Sutton and Theodor Boveri in 1902
suggested that chromosomes are the physical carrier
of genes in the eukaryotic cells.

Centromere or Kinetochore:

It is the primary constriction at the center to which the chromatids or spindle fibers are attached. Its function is to enable movement of the chromosome during the anaphase stage of cell division.

Chromatid:

Each chromosome has two symmetrical
structures called chromatids or sister chromatids which is
visible in mitotic metaphase.
› Each chromatid contains a single DNA molecule.

Chromatin:

It is a complex of DNA and proteins that forms
chromosomes within the nucleus of eukaryotic cells.

Thedarkly stained, condensed region of chromatin is
known as heterochromatin. It contains tightly
packed DNA, which is genetically inactive
 The light stained, diffused region of chromatin is
known as euchromatin. It contains genetically
active and loosely packed DNA

Telomere:

A telomere is the end of a chromosome. Telomeres are made of repetitive sequences of non-coding DNA that protect the chromosome from damage. Each time a cell divides, the telomeres become shorter. Eventually, the telomeres become so short that the cell can no longer divide.

Karyotype:-

The characteristics features of chromosome of a species is referred as karyotype
 Its phenotypic appearance of the chromosomes of a
particular species.

Two types – Symmetrical and Asymmetrical

Features taken into consideration in karyotype study
 1. Number
 2. Position of centromere
 3. Size
 4. Position of satellite
 5. Degree and distribution of heterochromatin

Special types of Chromosome :- 

- Polytene Chromosome :- 

Balbiani was first discovered a structure in the nuclei of secretory of midges (Chironomas) in 1881. 

-- Also known as the Salivary gland Chromosome. 

They are called polytene by Kollar due to pressence of many chromonemata in them. 

* Chromonemata - at the prophase, the chromosomal material is visible as their filament known as chromonemata. 

These are present in some cells of the larvae of Diptheria insects. 

these cells undergo repeated round of DNA replication without cell division. 

Chromosome puff or Balbiani rings are present which are the swelling of bands dueto DNA . 

unfolding into open loops. THese are the region of the intense transcription on mRNA formation. 

Lampbrush Chromosome - 

First discovered in the oocytes of Salamander by Fleming in 1882. 

The name is given due to its resemblance with a  brush that is used for cleaning lamp, glasses, chimney, etc. 

Lampbrush chromosome also found in the spermatocytes of many animals, 

they are present as a bivalent with 4 chromatids. 

Lamp brush chromosome are thought to assist in fulfilling the high demand for transcription oogenesis.