Chromosome and its Chromosome morphology structure P Victoria

Chromosome and its Chromosome morphology structure P. Victoria Rani Lecturer in Botany D. K. Govt Degree college for women (A), NELLORE Dr P. Victoria Rani Lecturer in Botany V Sem, Cell Biology Genetics and Plant Breeding (Paper V) D. K. Govt Degree college for women (A), NELLORE

INTRADUCTION � Chromosome means: chroma - colour; soma – body �A chromosome is a thread-like self-replicating genetic structure and containing organized DNA molecule. � Chromosomes are seen in the metaphase stage of mitosis. � Hofmeister in 1848 discovered thread-like structures from pollen mother cells of Tradescancia. � Waldeyer coined the term chromosome first time in 1888 � Chromosomes are considered as Vehicles of Heredity.

Number of chromosome � The number, size of chromosomes varies from species to species. � Diploid -The somatic chromosome number is the number of chromosomes found in somatic cell and is represented by 2 n (Diploid). � Haploid - The gametes have chromosome number is half of the somatic chromosome numbers and represented by n (Haploid). � Polyploidy –Cell contain more than two sets of chromosomes.

Number of chromosomes Download from https: //www. google. com

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Types of chromosomes � Chromosomes are of two types � Autosomes: That control somatic characters other than sex characters. � Sex chromosomes – Chromosomes involved in sex determination. Humans and most other mammals have two sex chromosomes X & Y, also called heterosome. � Females have two X chromosomes in diploid cells and males have an X and a Y chromosome.

The size of chromosome � Short as 0. 25 µm in fungi and some birds or as long as 30 µm in some plants like Trillium. Chromosome shape � 1. Telocentric � 2. Acrocentric � 3. Sub-metacentric � 4. Metacentric

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Chromosome Structure Chromosome consists � Pellicle � Matrix � Chromonema � Chromomeres � Centromere or primary constriction � Secondary constriction � Satellite bodies � Telomeres

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� Prophase and metaphase Download from https: //www. google. com

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Mitosis metaphase Download from https: //www. google. com

Functions of Chromosomes � Control the Heredity � Control the metabolism of an organism � Changes in the position, number and structure of Chromosomes lead to the formation of new species.

� Karyotype � It is refers to the entire set of chromosomes present in the cell. � Idiogram � The photograph showing the chromosomes of a cell.

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Chemical composition of chromosomes Proteins- 60% (protamines, histones) � DNA-35% � RNA-5% � Protamines � Basic protein rich in the basic amino acid orginine Histones � Rich in the basic amino acid orginine and lysine � Histones are H 1, � H 2 a � H 2 b � H 3 and � H 4.

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NUCLEOSOME The DNA wraps around the histone proteins to form a bead like structure which consist core, core DNA and linker DNA. Download from https: //www. google. com

Chromosome parts Heterochromatin. � compactly coiled regions � deeply stained � Silent genes with methylated � High AT content � less active Euchromatin � loosely coiled regions. � less stained � active or potentially active genes � genetically active

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