WHAT IS MUTATION- AN OVERVIEW & TYPES
Overview
- Mutation refers to sudden heritable change in an organism due to alteration in the nucleotide sequence of the genome of that organism.
- Mutation results from errors during DNA-replication, mitosis, and meiosis or other types of damage to DNA.
- Mutations may also result from insertion or deletion of segments of DNA due to mobile genetic elements.
- Mutation may be-
In a single gene, i.e. Gene mutation or Point mutation
Insertion or deletion of chromosome structure, i.e. chromosomal aberration
In the number of chromosomes, i.e. polyploidy= heteroploidy
In the plasma genes, i.e. plasma gene mutation (Plasma genes present in chloroplast or mitochondria etc. of the cytoplasm) - Mutations can involve the duplication of large sections of DNA, usually through exchange of genetic material between different organisms that produces offspring with combination of new traits. These duplication are a major source of raw material for evolving new genes.
- Changes within genes are called point mutations. Base sequence of genes is changed due to base pair transition, deletion, duplication or inversion.
Spontaneous Mutation
Such mutation occurs in nature without any treatment induced by man and frequency of such mutation is low. Spontaneous mutation can be characterized by the specific changes, such as
- Incorrect base pairing during replication
- Loss of purine base
- Replication slippage
- Miss pairing of slipped strand etc.
Induced Mutation
Such mutations are artificially induced by certain physical or chemical agents called mutagens. Chemicals such as Bromodeoxyuridine, Alkylating agents, ethidium bromide and ionizing and non-ionizing radiations are used.
By effect on structure and by impact on protein sequence type of mutation are classified. A brief description is given here.
- Base addition or deletion– insertion of one or more bases in a DNA molecule is called base addition, while the loss of one or more bases is called base deletion. Such addition or deletion alters the code word of gene that results into production of ineffective protein.
- Base substitution– A nitrogen base of triplet codon of DNA is replaced by another nitrogen base or its derivatives.
- Transition– here a purine is replaced by another purine, such as adenine is replaced by guanine or vice-versa; or a pyrimidine is replaced by another pyrimidine, e.g. thymine is replaced by cytosine or vice-versa.
- Transversion– the substitution or replacement of a purine by pyrimidine or vice-versa is called transversion. For example A to T, A to C, G to C, G to T & T to A, C to A, C to G, T to G.
Somatic Mutation
- A change in the genetic structure that is not inherited from a parent, and also not passed to offspring, is called a somatic/bud mutation.
- However, they are passed down to all the progeny of a mutated cell within the same organism during mitosis.
- These types of mutations are usually prompted by environmental causes, such as ultraviolet radiation or any exposure to certain harmful chemicals. With plants, some somatic mutations can be propagated without the need for seed production, for example, by grafting and stem cuttings.
- This type of mutation has led to new types of fruits, such as the “Delicious” apple.
Read more..
MENDEL’S LAW OF INHERITANCE
DIFFERENCE BETWEEN GENE AND ALLELE
MITOSIS & MEIOSIS- CELL DIVISION
CELL STRUCTURE AND FUNCTION
CROSSING OVER- PROCESS & FUNCTION
DIFFERENCE BETWEEN PROKARYOTIC AND EUKARYOTIC CELLS
DIFFERENCE BETWEEN PLANT CELL AND ANIMAL CELL
SYNAPSIS MEANING- PROCESS & FUNCTION