Model Answer
0 min readIntroduction
Induced mutation is a powerful tool in plant breeding, enabling the creation of novel genetic variations beyond what can be achieved through traditional hybridization. It’s a technique used to artificially induce changes in the genetic material of plants, leading to the appearance of desirable traits. The concept originated from the observations of Hermann Muller in the 1920s who demonstrated the mutagenic effects of X-rays on fruit flies. This technique provides a shortcut to overcome limitations in existing germplasm and generate plants with improved yield, disease resistance, or nutritional content.
What is Induced Mutation?
Induced mutation involves exposing plant material (seeds, seedlings, or pollen) to physical or chemical agents to induce genetic mutations. These mutations can be random and affect various genes, potentially creating new alleles or combinations of alleles that were not previously present in the population. This accelerates the process of genetic diversification.
Procedure for Utilization of Induced Mutation
The procedure for utilizing induced mutation in plant breeding typically involves the following steps:
1. Pretreatment
Prior to exposure to mutagens, plants are often pretreated to enhance mutation frequency. This can involve chilling, soaking in growth regulators like gibberellic acid (GA3), or exposing to stress conditions. Pretreatment increases the permeability of cell membranes, making them more susceptible to mutagenic agents.
2. Mutagen Treatment
This is the core step, involving exposure to either physical or chemical mutagens. Common mutagens include:
- Physical Mutagens: Primarily X-rays and gamma rays. These cause breaks in DNA strands.
- Chemical Mutagens: Examples include Ethyl Methane Sulphonate (EMS), Sodium Azide (NaN3), and nitrous acid (HNO2). EMS is particularly effective in inducing point mutations (base substitutions).
| Mutagen | Type | Mechanism | Effect |
|---|---|---|---|
| X-rays | Physical | DNA strand breaks | Chromosomal aberrations |
| Gamma rays | Physical | Ionizing radiation | Chromosomal aberrations |
| EMS | Chemical | Alkylation of guanine and adenine | Point mutations (base substitutions) |
| NaN3 | Chemical | Reaction with DNA bases | Base modifications |
3. Selection
Following mutagen treatment, seeds are sown and plants are screened for desirable traits. This can be done through visual observation, simple bioassays (e.g., for disease resistance), or more sophisticated molecular techniques. Selection can be done at various stages: seedling selection, plant selection, or even at the progeny level.
4. Evaluation and Stabilization
Selected mutants are then evaluated for their performance in replicated trials. The stability of the mutation is assessed through several generations. If the mutation is dominant or fully recessive, it can be stabilized through self-pollination or pedigree selection. Heterozygous mutants are often discarded, unless they possess a unique combination of desirable traits.
Advantages and Limitations
Induced mutation offers a rapid route to genetic improvement. However, mutations are random, and many are deleterious. The process requires considerable screening effort. Furthermore, the genetic basis of the induced traits may not always be fully understood.
Conclusion
Induced mutation remains a valuable tool in plant breeding, especially for creating variability when conventional breeding methods are less effective. While the process involves a degree of randomness and necessitates meticulous screening, the potential for generating novel traits with significant agronomic benefits continues to drive its application. Advancements in molecular techniques are further refining the process, allowing for more targeted and efficient mutation breeding programs.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.