Chromosomal aberrations -Structural change of chromosomes

Chromosomal Mutations-structural changes

Chromosomal aberrations The structure of chromosome may change. Such changes are called aberrations. They are four types.

I) Deletion, 2) Duplication, 3) Inversion, 4) Translocations.

Chromosome is an assemblage of genes arranged in a linear order. In a chromosome the number and position of genes are fixed. Hence if the position of gene is changed, in chromosome, it will change the phenotype. The structural change of a chromosome is inherited. Previously these changes are considered as chromosomal mutations. Now days they are called as chromosomal aberrations.

 

Deletion in Chromosomes

Sometimes the chromosome may lose a fragment Hence one or few genes are lost. This is called deletion. In a A, B, C, D, E, F, G,  chromosome  because of which some intrinsic, or extrinsic cause a small fragment may lost. The chromosome becomes A, B, ,E, F G. It has lost G. fragments. Hence it is called Deletion. Deletions are rare. Deletion may occur on one chromosome of a homologous pair. Then the recessive genes may be expressed. In this way phenotype characters are changed. They are hereditary. This is called Deletion. Ultraviolet rays bring deletions.

 

Duplication in Chromosomes

It is opposite of deletion. In meiosis as a result of Unequal crossing over a small fragment is added more to the chromosome.. This is called Chromosomal Duplication. In a chromosome A, B, C, D, E, F, (3, Fl.- If A, B is added then the chromosome will become A, B, A, B, C, 0, E, F, G, H this Is called duplication. Usually the additional genes will come from homologous chromosomes.

The appearance of bar eye character in Drosophila. Morgan and Strutevant described the bar locus in the salivary gland chromosome of Drosophila.

 

 

 

 

Inversion in Chromosomes: It is another type of chromosomal rearrangement. in this type the order of genes in the chromosome will change, in ABCDEFG chromosome because of inversion the gene order is changed as ABEDCFG. This is called inversion. This may be brought forward by x-ray radiation.

 

Translocations in Chromosomes

Sometimes a segment of one chromosome will break, and is transferred to -another non-homologous chromosome. Such transfer is called  translocation. It is called segmental inter change. It is resulted because of illegitimate crossing over. In general X-rays and other ionizing radiations will bring chromosomal aberrations.

also know more about Polyploidy and neo Darwinism