Chromosome Structure
Chromosome
Chromosomes are thread like structure present inside the nucleus . This chromosomes play a wide role in heredity hence they are also called carriers of heredity . The word Chromosome is derived from two Greek words - Chroma - Color and Soma - Body . Generally they are found in pairs and vary with organisms like in human they are 23 , elephants 28 , cat have 19 pairs of chromosomes .
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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