What are the Differences between Chromosomes, Chromatids and Chromatin

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Definition: Chromosome

A thread-like structure of nucleic acids and proteins found in the nucleus of most living cells, carrying genetic information in the forms of genes.

Definition: Chromatid

Each of the two thread-like strands into which a chromosome divides longitudinally during cell division. Each contains a double-helix of DNA.

Definition: Chromatin

The material of which the chromosomes of organisms other than bacteria (i.e. eukaryotes) are composed, consisting of proteins, RNA and DNA

Chromosomes are structures into which DNA (the code of life) is organized. Chromosomes are linear in Eukaryotic cells and circular in Prokaryotic cells. The number of chromosomes are different in different organism. Kangaroos have 12 chromosomes, dogs have 78 and we (humans) have 46. The total length of human chromosomes is about 2m in length. This vast length has to be packed in nucleus of about 5 to 10 microns!

To do this, they have a unique packaging system, in which DNA wraps around an octomer (eight protein complex) called histone. This results in a beads-on-string structure or Nucleosome. This is called Chromatin. The nucleosomes condense to form a chromatin fibre. Chromatin fibre organizes into chromosomes during cell-division. The chromosomes are in pair; each part is called Chromatid. These chromatid are joined together at centromeres.

Multiple Choice Questions

The correct order is:
(1) Chromosomes -> Nucleosomes -> Telomeres -> DNA -> Chromatids
(2) Chromosomes -> Centromere -> gene -> DNA -> Histones
(3) Chromosomes -> Nucleosomes -> gene -> DNA -> Nucleotides
(4) Chromosomes -> Base Pairs -> gene -> DNA -> Nucleosome

Ans: http://zoomgenetics.apphb.com/?id=m90

The fundamental packing unit of chromatin is called
(1) histone
(2) chromatid
(3) nucleosome
(4) nucleoside

Ans: http://zoomgenetics.apphb.com/?id=m242

Nucleosomes consists of eight proteins known as histones, with approximately ____ base pairs of DNA wound around them.
(1) 47
(2) 147
(3) 247
(4) 347

Ans: http://zoomgenetics.apphb.com/?id=m187

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