Mutation: Sudden and abrupt changes to the genetic material of organisms.
→ Spontaneous change by mutagens that affect on the DNA or the genes or sometimes the complete chromosome.
Table of Contents
A.) CHROMOSOMAL MUTATION
→ A parmanent change in the number of chromosome or structure of chromosome of a organisms is called chromosomal mutation.
Two types
- (i) Mutation in chromosomal Structure
- (ii) Mutation on chromosomal Number.
→Variation in chromosomal structure / number is called chromosomal aberration.
(i) Mutation on Chromosomal Structure
Structural changes are relatively few in nature and these can be frequently produced by the lonizing radiation like X-rays, atomic radiation and chemical mutagens – Mustard gas
Four types: ① Deletion ② Duplication ③ Inversion ④ Translocation
When structural changes occur in both chromosome of a homologous pair, these are called structural homozygotes. If structural change occurs in one chromosome of a pair, it is called structural heterozygote.
① Deletion
→ The loss of segment of the genetic material in a chromosome is called deletion.
Two types: (i) Terminal & (ii) Intercalary deletion.
(i) Terminal Deletion: When the chromosomal deletion is occurs near the end of the chromosomes than it is called terminal deletion.
Example: Pseudodominance
(ii) Intercalary Deletion : When the deletion is occurs middle part of the chromosomes than it is called intercalary deletion.
② Duplication:
→The segment of the genetic material in a chromosome is called duplicated is duplication.
Eg. Bar eye in Drosophilia
Three types: i)Tandem ii)Reverse tandem iii) Displaced duplication
(i)Tandem duplication: The segment is duplicated or repeated just after its normal position.
(ii) Reverse tandem duplication: The segment is duplicated and repeated in reverse order on same chromatid.
(iii) Displaced duplication: The segment is duplicated and repeated in distant place from its normal position.
Two types – (a) Homobranchial & (b) Heterobranchial duplication
a) Homobranchial duplication: Ther segment is duplicated and repeated in distant place of same chromatid.
b) Hetero branchial duplication: The segment is duplicated on the other chromatid.
③ Inversion:
In Inversion part of chromosome is rearranged in reverse order. In inversion the Chromosome break at two parts, the broken segment rotates to 180, the rotated part reunited reversing the gene sequence.
Two types – (1) Paracentric and (2)Pericentric inversion
1.) Paracentric Inversion: The segment without centromere rearranged and rotated 180 then is called paracentric inversion.
2.) Pericentric Inversion: The segment with centromere rotate 180° and arranged in the chromosome.
④ Translocation
The translocation is inter chromosomal or intra chromosomal rearrangement by exchange of chromosomal segment.
→ Exchange of segment between two non homologous chromosome.
4 four types – (i) Simple translocation (ii) Shift translocation (iii) Reciprocal translocation (iv) Robertsonian translocation
(i) Simple translocation. The end segment one chromosome is add with a other non- homologous chromosome.
(ii) Shift translocation : When the middle segment of a chromosome added or translocate into a other non-homologus chromosome.
(iii) Reciprocal translocation: When one segment of a chromosome exchanged by another segment of a different non-homologous chromosome between eachother
(iv) Robertsonian translocation: the When two A Chromosome degenerate and the long arm form a chromosome non-homologous chromosome.