Deletion and Duplication of Chromosomes

Structural Abberrations, Deletion, Duplication, Chromosomes

1. Presented By- Sanjeev Mishra MSB/20/150 Topic:- Deletion And Duplication

2. Structural Aberrations The chromosomal aberrations in which alternation of the structure of chromosome(sequence of genes or kind of genes in chromosome or no. of genes)occur—Structural Aberration. Types of Structural aberrations:- Changes in number of genes Deletion (Terminal, Intercalary) Duplication (Intrachromosomal, Interchromosomal) Changes in the location of genes Inversions (Paracentric, Pericentric) Translocations (Intrachromosomal, Interchromosomal)

3. Deletion It is a loss of a (generally small) segment of chromosome during replication process. Any number of  nucleotides  can be deleted, from a single  base  to an entire piece of chromosome. It can be Spontaneous or may be induced (radiation, UV, chemicals, viruses). Detection is based on unpaired region of normal chromosome that produces a loop during pachytene stage. Firstly, observed by Bridges in 1917 in Drosophila. Terminal deletion : It is a l oss of either terminal segment of a chromosome. In 1938, Muller postulated that loss of telomere makes chromosome unstable, so it is not commonly observed. Ex:- maize. b) Intercalary deletion : It is a loss of segment in between centromere and telomere.

4. Duplication The occurrence of a segment twice in the same chromosomes is known as duplication. It occurs due to unequal crossing over or crossing over in inversion or translocated heterozygotes. It is detected by presence of loop in duplicated region during pachytene stage. Intrachromosomal Duplication : Tandem – In this case sequence of genes in the duplicated segment is similar to the sequence of genes in the original segment of a chromosome. Reverse tandem – The sequence of genes in the duplicated segment is reverse to the sequence of genes in the original segment of a chromosome. Interchromosomal Duplication : Displaced - Duplicating segment is incorporated away from corresponding segment on the same chromosome. Translocated - Duplicated chromosomal segment is incorporated on different chromosome.

5. Effects Of Deletion & Duplication Deletion :- Crossing over not occur. Harmful effect on diploid organisms. Morphological effects. Duplication :- Origin of new genes mainly due to duplication results in evolution. Activity of certain enzymes may be doubled.