Associate Professor and Head Department of Sericulture Yuvarajas College University of Mysore Mysore India 11Sep20 1 wwwhbmaheshweeblycom CHROMOSOMES The chromosomes are nuclear components of special organization individuality and function They are capable of self reproduction ID: 932059
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CHROMOSOMES
Dr. Mahesha H BAssociate Professor and HeadDepartment of SericultureYuvaraja’s College, University of Mysore, Mysore, India
11-Sep-20
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Slide2CHROMOSOMES
The chromosomes are nuclear components of special organization, individuality and function. They are capable of self reproduction and play a vital role in heredity, mutation and evolution.11-Sep-202
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Slide3Chromosomes were first described by Strausberger
in 1875. The term “Chromosome”, however was first used by Waldeyer
in 1888
. They were given the name chromosome (Chromo = colour; Soma = body) due to their marked
affinity for basic dyes
.
Their number can be counted easily only during
mitotic metaphase.
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Slide4Number of chromosomes
Normally, all the individuals of a species have the same number of chromosomes. Closely related species usually have similar chromosome numbers. Gametes normally contain only one set of chromosome – this number is called
Haploid : n
Somatic cells usually contain two sets of chromosome - 2n : Diploid
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Slide5Chromosomes in different species
Table 1: Examples of chromosome numbers (diploid).
Species
No. of chromosomes
Species
No. of chromosomes
Fruit fly
8
Human
46
Pig
40
Ape
48
Guinea Pig
16
Sheep
54
Wheat
42Horse64Edible snail24Silkworm56Earthworm36Fern~1200Butterflies~380Onion16
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Slide6Size of the Chromosomes
In contrast to other cell organelles, the size of chromosomes shows a remarkable variation depending upon the stages of cell division. i.e.,Interphase, Prophase, Anaphase & Metaphase. Therefore, chromosomes measurements are generally taken during mitotic metaphase.Length 1μ – 30
μ
Dia 0.2 μ – 20
μ
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Slide7Types of Chromosomes
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Slide8Structure of Eukaryotic Chromosomes
Structure of a metaphase chromosome
A-External Structure
1.Secondary constrriction
2.Satellite
3.Primary constriction or centromere
CHROMATIDS > CHROMONEMATA
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Slide9B-Internal Structure
1.Two chromonemata2.Satellite
3.Centromere
A. Nucleolus organizer
B. Chromosome
C. Nucleolus
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Slide10Euchromatin- large amount of DNA, Small amount of RNA and certain Basic proteins & Takes deep stain by basic stains
HeteroChromatin - large amount of RNA, Small amount of DNA and certain Acidic proteins & Takes light stain by basic stains11-Sep-20
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Slide11Chromatin Structure Chromatin =DNA+Protein complex
In Humans 2.2 meters of DNA distributed in 46 ch’somes Each ch’somes contain 4.8 cm condensed to 6 Microns i.e., packing ration 8000:1
DNA
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Slide12Chromatin Structure :
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Slide13Special chromosomes
Polytene Chromosomes: occurs in certain tissues salivary glands, trachea, fatbody cells and malphighian tubules of Dipterians.
Eg., Drosophila
First observed by Balbiani
- 1881
The name was suggested by
Kollar
Measures 200 micron against 7.5
DNA 1000 times more due to
endomitosis
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Slide14Polytene Chromosomes
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Life Cycle of Drosophila
Collection of Salivary Glands
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Slide15Polytene Chromosomes
Dark bands are euchromatinLight bands are heterochromatin
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Slide16Schematic drawing shows the organization of the chromosome (chromatids,
chromomeres, chromosome bands). The lower figure exhibits the change in chromosome structure upon puff formation at one locus. These puffs are active genes and represents site of RNA synthesis
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Slide17Lamp brush Chromosome:
Found in animal Oocytes eg., fishes, birds, reptiles and birdsLength & Breadth is 1000 & 20 microns respectivelyCh’somes composed of Main axis & Loops
.Loops are rich in
RNA and Protein synthesis
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Slide18Acknowledgements to
INTERNETFOR
PICTURES
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