What mutagens to use to make a new phenotype in a plant?
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08-14-2013, 05:11 PM
(This post was last modified: 08-14-2013, 05:36 PM by Administrator.)
Mutation refers to any alteration in the genetic material of an organism be it humans, bacteria, viruses etc. Mutation occurs when there is damage to the genetic material (DNA or RNA) during replication which gets overlooked during proof reading stage of replication. Mutation may also occur due to an insertion or deletion leading to a frame shift.
A mutation in the nucleotide sequence may or may not result in any physical (phenotypical) change. It can cause a change in expression of the nucleotide sequence i.e. a change in the mRNA formed and ultimately the protein. Mutations are capable of inactivating a gene, and are responsible for genetic disorders and even cancer. Depending on the stability (or lack thereof) a mutation may or may not be passed on to future generations.
Mutagenesis is basically voluntary generation of a stable mutation to produce a desired character. Even though mutagenesis in nature is rarely favorable, mutagenesis in laboratory can be controlled to give desired products.
It was developed in the 20th century based on the works of Muller, Auerbach, and Robson who worked together on X ray mutagenesis and the effects of mutagens like mustard gas on fruit flies.
Mutagenesis has been performed on plants like Arabidopsis, aims at causing maximum genetic variation with minimum decrease in variability.
Even though X –ray mutagenesis was the first and most preferred method, it has now been replaced by gamma-irradiation and fast neutron bombardment.
Chemical mutagens have also become extremely popular because of their comparatively hassle –free nature and easy availability. They generally cause deletions and translocations in the nucleotide sequences. Among chemical mutagens, EMS (ethyl methanesulfonate) is today the most widely used. EMS selectively alkylates guanine bases causing the DNA-polymerase to favour placing a thymine residue over a cytosine residue opposite to the O-6-ethyl guanine during DNA replication, which results in a random point mutation. A majority of the changes (70–99%) in EMS-mutated populations are GC to AT base pair transitions. Other mutagens such as sodium azide (Az) and methylnitrosourea (MNU) are also used and often combined into an Az-MNU solution. Genetically, Az-MNU predominantly causes GC to AT shifts, or AT to GC shifts. Thus, contrary to EMS, a shift can happen in either direction. All three chemical mutagens are, as can be expected, strongly carcinogenic and should be handled with extreme care. Unlike EMS, MNU is both sensitive to shock and unstable above 20°C making it complicated to work with. In contrast to EMS and MNU, which are both liquid, Az is a solid dust in its ground state and the additional step of first dissolving the acutely toxic and volatile substance before application makes it less attractive to handle.
Through the years, mutagenesis has generated a vast amount of genetic variability and has played a significant role in plant breeding programs throughout the world. Notable examples are several wheat varieties (e.g., durum wheat used in pasta), barley including malting barley, rice, cotton, sunflower, and grapefruit, resulting in an enormous positive economic impact.
A mutation in the nucleotide sequence may or may not result in any physical (phenotypical) change. It can cause a change in expression of the nucleotide sequence i.e. a change in the mRNA formed and ultimately the protein. Mutations are capable of inactivating a gene, and are responsible for genetic disorders and even cancer. Depending on the stability (or lack thereof) a mutation may or may not be passed on to future generations.
Mutagenesis is basically voluntary generation of a stable mutation to produce a desired character. Even though mutagenesis in nature is rarely favorable, mutagenesis in laboratory can be controlled to give desired products.
It was developed in the 20th century based on the works of Muller, Auerbach, and Robson who worked together on X ray mutagenesis and the effects of mutagens like mustard gas on fruit flies.
Mutagenesis has been performed on plants like Arabidopsis, aims at causing maximum genetic variation with minimum decrease in variability.
Even though X –ray mutagenesis was the first and most preferred method, it has now been replaced by gamma-irradiation and fast neutron bombardment.
Chemical mutagens have also become extremely popular because of their comparatively hassle –free nature and easy availability. They generally cause deletions and translocations in the nucleotide sequences. Among chemical mutagens, EMS (ethyl methanesulfonate) is today the most widely used. EMS selectively alkylates guanine bases causing the DNA-polymerase to favour placing a thymine residue over a cytosine residue opposite to the O-6-ethyl guanine during DNA replication, which results in a random point mutation. A majority of the changes (70–99%) in EMS-mutated populations are GC to AT base pair transitions. Other mutagens such as sodium azide (Az) and methylnitrosourea (MNU) are also used and often combined into an Az-MNU solution. Genetically, Az-MNU predominantly causes GC to AT shifts, or AT to GC shifts. Thus, contrary to EMS, a shift can happen in either direction. All three chemical mutagens are, as can be expected, strongly carcinogenic and should be handled with extreme care. Unlike EMS, MNU is both sensitive to shock and unstable above 20°C making it complicated to work with. In contrast to EMS and MNU, which are both liquid, Az is a solid dust in its ground state and the additional step of first dissolving the acutely toxic and volatile substance before application makes it less attractive to handle.
Through the years, mutagenesis has generated a vast amount of genetic variability and has played a significant role in plant breeding programs throughout the world. Notable examples are several wheat varieties (e.g., durum wheat used in pasta), barley including malting barley, rice, cotton, sunflower, and grapefruit, resulting in an enormous positive economic impact.
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