Chromosome

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The Y chromosome become brightly fluorescent both in the interphase and in metaphase.

3. R banding:

The R bands (from reverse) are those located in the zones that do not fluoresce with the quinacrine mustard, that is they are between the Q bands and can be visualized as green.

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4. G banding:

The G bands (from Giemsa) have the same location as Q bands and do not require fluorescent microscopy.

Many techniques are available, each involving some pretreatment of the chromosomes.

In ASG (Acid-Saline-Giemsa) cells are incubated in citric acid and NaCl for one hour at 600C and are then treated with the Giemsa stain.

5. C banding:

The C bands correspond to constitutive heterochromatin.

The heterochromatin regions in a chromosome distinctly differ in their stainability from euchromatic region.

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VARIATION IN STRUTURE OF CHROMOSOME

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Chromosomal Aberrations

The somatic (2n) and gametic (n) chromosome numbers of a species ordinarily remain constant.

This is due to the extremely precise mitotic and meiotic cell division.

Somatic cells of a diploid species contain two copies of each chromosome, which are called homologous chromosome.

Their gametes, therefore contain only one copy of each chromosome, that is they contain one chromosome complement or genome.

Each chromosome of a genome contains a definite numbers and kinds of genes, which are arranged in a definite sequence.

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Chromosomal Aberrations

Sometime due to mutation or spontaneous (without any known causal factors), variation in chromosomal number or structure do arise in nature. - Chromosomal aberrations.

Chromosomal aberration may be grouped into two broad classes:

1. Structural and 2. Numerical

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Structural Chromosomal Aberrations

Chromosome structure variations result from chromosome breakage.

Broken chromosomes tend to re-join; if there is more than one break, rejoining occurs at random and not necessarily with the correct ends.

The result is structural changes in the chromosomes.

Chromosome breakage is caused by X-rays, various chemicals, and can also occur spontaneously.

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There are four common type of structural aberrations:

1. Deletion or Deficiency

2. Duplication or Repeat

3. Inversion, and

4. Translocation.

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