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Chromosomes – Structure ,Types and Functions
Chromosomes ,Structure ,Functions
Dr.V.Malathi
Structure of Chromosomes
Each chromosome has a constriction point called the centromere. The centromere divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the The long arm of the chromosome is labeled the The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.
Types of Chromosomes
Apart from the two types of chromosomes namely Autosomes and Allosomes , Chromosomes may be classified further :
I. On the basis of location of centromere
- Telocentric– Telocentric chromosomes have the centromere at the end of the chromosome . Here centromere occupy the terminal position. Thus, the chromosome in this case has just one arm. Such rod shaped chromosomes are found in species such as mice.
- Acrocentric- In this type ,centromere occupying a sub-terminal position making one arm very long and the other very short. Human chromosomes 13, 15, 21, and 22 are acrocentric.
- Sub-metacentric– This type of chromosomes are with centromere slightly away from the mid-point. The two arms are unequal. Human chromosomes 4 through 12 are sub-metacentric.
- Metacentric- Metacentric chromosomes are V-shaped . The centromere lies in the middle of chromosome or in the center. The two arms are almost equal. Human chromosome 1 and 3 are metacentric.
II. On the basis of number of centromere
- Monocentric- Chromosomes are with one centromere.
- Dicentric-Chromosomes with two centromeres.
- Polycentric- Chromosomes with more than two centromeres.
- Acentric- Such chromosomes are without centromere. These are freshly broken segments of chromosomes.
- Diffused or non-located- These are chromosomes with indistinct centromere diffused throughout the length of chromosome.
Functions of Chromosomes
- Chromosomes are the essential unit for cellular division
- Chromosomes must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of their progeny.
- Chromosomes protect the DNA from damage
- The dynamics of chromosome structural changes regulate gene expression.
- Chromosomal recombination plays a vital role in genetic diversity.
The short arm of the chromosome
The long arm of chromosome