What is Chromosome? | Structure and Types of Chromosomes

The thread-like structure that appears inside the nucleus at the time of cell division is called a chromosome.

Discovery of chromosomes:

German embryologist Walther Flaming was examining rapidly dividing cells of salamander larvae. He observed chromosomes in 1882. Chromosomes are found in the cells of all eukaryotes. However, their number varies from species to species.

Number Of Chromosomes In Different Species:

Fungus	2
Ferns	500
Mosquitos	6
Honey bee	32
Corn	20
Sugar Cane	80
Frog	40
Human	46

Autosomes and sex chromosomes

Sex chromosomes are the chromosomes that carry genes that determine sex. While autosomes are not linked with sex-related genes. Male and females have the same copy of autosomal chromosomes. Sex chromosomes are different in males and females. Sex chromosomes in males are XY and XX in females.

Composition Of Chromosomes:

A chromosome is made of a chromatid, centromere, primary construction, and secondary constriction. Chromosomes are widely different in appearance. They show particular Organization of chromosomes.

They vary in size, staining properties, location of centromere, relative length of two arms on either side of the centromere, and the opposition of constructed region along the arms.

Karyotype

The particular arrangement of a chromosome that an individual possesses is called its karyotype. Different species have different karyotypes. Sometimes individuals of the same species have different karyotypes.

Shapes of chromosomes:

Chromosomes acquire different shapes at the time of cell division the usual types are I and J and V.

Types of chromosomes:

Chromosomes have different types based on the position of the centromere.

Telocentric:

The centromere is present at the ends of the chromatids.

Acrocentric:

The centromere is present near the end of the chromatid.

 Sub metacentric:

The centromere is present nearby the middle of the chromatids.

Metacentric:

The centromere is present in the middle of the chromatids.

Chemical Composition Of Chromosomes

Chromosomes are composed of DNA and protein. Chromosomes have about 40% of DNA and 60% protein. DNA synthesizes RNA, thus a large amount of RNA is also associated with chromosomes.

Length of Chromosome

The DNA of a chromosome is very long. It is double-stranded fiber. It extends unbroken through the entire length of the chromosome.

Number of Nucleotides in Chromosome

A typical human chromosome contains about 140 million nucleotides in DNA. Suppose the is nuclear tied is equal to avoiding each page of a book that has about 500 words on it one chromosome can feel about 280 printed books of 1000 pages.

Coiling of Chromosomes:

If the strand of DNA from a single chromosome is spread in a straight line. It will be about 5cm long. Nature has fit such a strand of only 1 of 46 into a small space of nucleus and chromosomes.

The DNA is in a coiled form in the cell. Thus it is fit into a small space. The DNA fibers coil tightly. The DNA resembles a strand of beads.

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