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