Intrachromosomal Aberrations

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Intrachromosomal Aberrations

Intrachromosomal Aberrations
When aberrations remain confined to a single chromosome of a homologous pair, they are called intrachromosomal or homosomal aberrations. These are of following kinds:
1. Deficiencies (Deletions)
In deletion or deficiency type intrachromosomal abberration a chromosome lacks either in an interstitial or terminal chromosomal segment which may include only a single gene or part of a gene. If break occurs neat the end of a chromosome; a small piece of the terminal end is lost and thus, terminal deficiency occurs. Sometimes. two breaks may occur at any two points, releasing an intercalary segment which may remain rod-shaped or may become ring-shaped. if its broken ends join and fuse. If, this ring-shaped chromosome (called deletion ring) has centromere it persists, but if lacks in that. loses during cell division.

The broken ends of original chromosome are fused and has intercalary or interstitial deficiency. If this chromosome has centromere it persists otherwise lost during cell division.

Both types of deficiencies are observable during meiotic pachynema or in the polytene chromosome. Because. Homologous chromosomes have strong tendency of pairing and of achieving an exact opposition of homologous parts, therefore, when a member of a homologous pair has an interstitial deficiency and other member remains normal, then, during pairing a bulging out as an unpaired loop, by the portion of the normal chromosome homologous to the deficient segment take place.

A. Interstial deficiency	B.Terminal deficiency
C.Formation of an acentric rod and deletion ring

Deficiency loop in the paired X-chromosomes from a salivary gland cell of a Drosophila larva heterozygous for notch

Such loops are called as deficiency loops and observable during meiotic prophase.
In some organisms terminal deficiencies are more common (i.e., maize) than in others (i.e., Drosophila) which may be related to differences in repair systems or stability of open breaks.

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