Chromosomes: Structure, Function, and Karyotyping, Study Guides, Projects, Research of Genetics

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CHROMOSOMES

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Chromosome

• Genes, the unit of inheritance are located on the chromosomes of the gametes.
• Passed from parents to progeny.
• Chromosome term was introduced by Waldeyer in 1888.
• Number of chromosomes is fixed in each cell but varies from species to species.
• In human beings, the total number is 46 or 23 pairs named as ‘diploid’ (2n).
• While in gametes (male or female) the number is 23 i.e. ‘haploid’ (n).
• 22 pair chromosomes are autosomes while 1 pair is sex chromosome.
• Length: 4-6 μ

Chemical Constituents

• DNA
• RNA
• Histones (basic in nature)
• Non-histone proteins (acidic in nature)

Structure of one Chromosome

Secondary Constriction

TELOMERE

• At two ends of chromosome
• Highly stable
• Made up of loops of chromatin fibers
• Maintenance of structural integrity

Chromatin

• Coiled strands of DNA bound to basic proteins (histones).
• 2 types: (1) Euchromatin (2) Heterochromatin
• Basic structural unit: Nucleosome

Solenoid model

• It was proposed by Kornberg and Thomas in 1974.
• Chromatin composed of a repeating unit called as nucleosome.
• Nucleosome consist of- A nucleosome core Linker DNA One molecule of 1HI histone Other associated chromosomal proteins