PPT on Chromosomes

1. Chromosomes
Mrs. Savreet Goraya
Asst. Prof. In Zoology

2. Chromosome structure

3. Chromosomes vs. Chromatin
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Chromosomes
Tightly packaged DNA
Found only during cell
division
DNA is not being used for
macromolecule synthesis
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Chromatin
Unwound DNA
Found throughout
Interphase
DNAis being used for
macromolecule synthesis

4. Homologous Chromosome Pairs

5. Autosomes & Sex Chromosomes
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Autosomes: Found in both males and females
In humans there are 22 pairs of autosomes
Autosomes that are the same size (& structure) are called
homologues
Sex Chromosomes: Determine an individual’s gender
One pair of chromosomes (X and Y)
The X and Y chromosomes are not homologous
The X chromosome is much larger than the Y chromosome
and contains many genes
The Y chromosome has only a small number of genes
In humans and other mammals females are XX and males
are XY

8. Chromosome structure
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Tertiary packaging of DNA into Chromosomes
The nucleosome histones (H2A, H2B, H3, H4)
The histone octamere
Histone H1 the linker histone
Higher order compactions

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Histone proteins
basic (+ charged
lysine & arginine)
amino acids that
bind DNA backbone
Four core histones in nucleosome
Two of each of H2A, H2B, H3 & H4
Fifth histone, H1 is the linker histone
Nucleosomes

10. Nucleosomes

12. Compaction level
in euchromatin
Compaction level in
heterochromatin
During interphase
most chromosomal
regions are
euchromatic

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Compaction level of interphase chromosomes is
not uniform
Euchromatin
Less condensed regions of chromosomes
Transcriptionally active
Regions where 30 nm fiber forms radial loop domains
Heterochromatin
Tightly compacted regions of chromosomes
Transcriptionally inactive (in general)
Radial loop domains compacted even further
Heterochromatinvs Euchromatin

15. Types of Heterochromatin
Figure 10.20
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Constitutive heterochromatin
Always heterochromatic
Permanently inactive with regard to transcription
Facultative heterochromatin
Regions that can interconvert between euchromatin and
heterochromatin
Example: Barr body

16. Thank You