Yasmeen Al wasel
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*Chromosome Banding
Chromosome Number Two types of
chromosomes:
Autosomes: all chromosomes other than sex
chromosomes and occur in the same frequency
in both sexes
Sex chromosome: X and Y chromosomes that
determine sex
Diploid organisms - 2n = 2x
n = gametic number haploid genome
2n = zygotic number diploid (2 x gametes)
x = basic number (one set)
Chromosome Banding Why to study Banding pattern?
This allows you to see smaller pieces of the chromosome, like
smaller structural chromosome abnormalities not visible on a
routine analysis.
Chromosomal banding techniques
In chromosome banding, we treat chromosomes with
chemicals to stain them and learn about a chromosome by
how it stains. There are several different types of stains we
can use.
There are several types of chromosome banding. Here, we
will list a few of the most common types.
1. G-(Giemsa(
2. R-(reverse)
3. C-(centromere(
4. Q-(quinacrine) banding.
They are most common methods of dye based chromosome banding
The types of banding techniques are ; 1. Q-Banding or Fluorescent Banding.
(a) with quinacrine mustard (QM) or quinacrine dihydrochloride (Q)
(b) with Hoechst 33 258
(c) with chromomycin and DAPI.
(d) D-bands with antibiotics
(e) Ethidium bromide as counter stain for Quinacrine with other chemical
2. G- Banding or Giemsa banding /GTL Banding
(a) with Giemsa
(b) with feulgen.
3. C- Banding
(a) CT- Banding
(b) Cd- Banding.
4. R- Banding or reverse banding
(a) Giemsa Reverse banding
(b) R- Banding by Fluorescence using a cridine orange (AO)
5. T-Banding
6. O-Banding or orcein banding
7. N-Banding /NOR staining (Silver Nuclear organizing region staining)
8. Hy- Banding.
9. Restriction enzyme banding.
Causes of banding
Occurrence of repetitive DNA.
Difference in base composition of DNA.
Difference in protein component.
Difference in the degree of packing of DNA or DNA complex.
Classification of bands
Based on the techniques used
• Constant heterochromatic bands
• Serial or Fluctuant bands
• Kinetochores.
Constant heterochromatic bands
• Visible in interphase and throughout division.
• Constant in size.
• Equivalent to C, GII and n bands.
• Associated with highly repetitive DNA.
eg: bands in plants, insect, amphibia..
Fluctuant bands
• Not distinguishable in interphase.
• change in size throughout mitotic prophase. .
• Equivalent to Q,G, and R bands.
• appear to be centers of mitotic chromosome
condensation.
eg: higher vertebrates- some insects.
Kinetochores
Eiberg’s Cd- banding technique reveals pairs of dots
at the centromers.
Uses of Chromosome Banding
G-and R-banding are the most commonly used techniques for
• chromosome identification (karyotyping(
• Identifying abnormalities of chromosome number, translocations
of material from one chromosome to another, deletions, inversions
or amplifications of chromosome segments.
Comparisons of chromosome banding patterns can confirm
evolutionary relationships between species and also reveal changes
in karyotype that may have been important in speciation.
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2 Chromosome
Banding