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What Are Chromosomes? Definition, Function, and Structure

                                          Chromosome




Chromosomes are thread-like structures found inside the nucleus of every cell. These structures play a crucial role in heredity, which is why they are often called the carriers of heredity.

The word “Chromosome” comes from two Greek words:

  • Chroma – meaning color

  • Soma – meaning body

Chromosomes are usually present in pairs, and their number varies among different organisms:

  • Humans have 23 pairs (46 chromosomes)

  • Elephants have 28 pairs

  • Cats have 19 pairs

These chromosomes carry genetic material in the form of DNA, which is passed on from one generation to the next.



Structure Of Chromosomes -   In 1888 W. Waldeyer called  this thread like structure a Chromosome as they could be stained with the help of stains like acetocarmine , acetoorcein etc . The structure of chromosome are composed of following parts -



  • Pellicle -    Each chromosome is bounded by membrane called Pellicle .
  • Matrix -  The  jelly like structure present inside chromosome enclosed by pellicle is known as Matrix
  • Chromatids - Chromatids  is the  two strands of  DNA that make  Chromosomes . Two chromatids are joined by a centromere . During prophase and sometime during interphase , the chromosomal material becomes visible as very thin filaments called as Chromenemeta .
  • Chromomere - Chromomere is one of the serially aligned beads that are linearly arranged along the chromosomes  They are also known by another name Idiomere .
  • Telomere -  The round sealed tips of chromosomes are known as Telomere . It is derived from the two Greek words - Telos - End and Meros  - Parts.  Telomere protect the end of chromosomes from fusion with neighboring chromosomes .
  • Centromere  or Primary Constriction -  It is the modified part of chromosomes where chromosomes threads are connected together .
  • Secondry Constriction -  It is different from the  primary constriction by angular  deviation of chromosomal segment during anaphase stage . It is the morphological feature of some types of chromosomes which  helps in their identification .
  • Satellite -  The terminal portion of chromosomes are known as Satellite . It is generally round in shape . The chromosome with satellite is known as SAT - Chromosome .


Function Of Chromosomes -


  • Chromosomes are carrier of gene (DNA ) .
  • Chromosomes are responsible for the transmission of parental character to their offspring .
  • Changes in the number of chromosomes are result in the development of new character .
  • They are responsible fro forming of new species .
  • Some chromosomes are called as Sex Chromosomes are help in determining sex of the individual .


Types Of Chromosomes - Depending upon the number their are four types of chromosomes -


  • Monocentric - When one centromere is present in each chromosomes then such type  of chromosomes are known as Monocentric .
  • Dicentric - in this type of chromosomes their are two centromere is present .
  • Polycentric - when their is more than two centromere present inside the chromosomes then the term polycentric is used .
  • Acentric - In this type of chromosomes their is no centromere present inside the chromosome  .



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