Different types of mutation depending upon its effect.
The mutation which affects the outer characteristic or physical characteristic of an organism is called as a morphological mutation. This type of mutation alters the physical properties like shape, size and colour of an organism.
A mutation which causes the death of an organism or affects the survival of an organism is called as a lethal mutation. If a mutation causes death in a certain environment than the mutation is called as a conditional lethal mutation.
In this type of mutation, the mutant allele causes mutant phenotype in a certain specific environment while remaining wild type in some other environment.
The conditions which favour the growth of mutant colonies are called restrictive conditions. In contrast, conditions which cause the growth of wild-type phenotype (having wild-type allele) are called as permissive conditions.
Conditional mutation is very important in genetic studies. We can study the characteristic of an allele, and how it behaves in different adverse conditions. We can also estimate the time duration of gene action.
Read next article: Mutation class 1: What is mutation
Each cell required energy and nutrients for differentiation and survival. Different biochemical pathway inside the cell provides that essential requirement. For mutation study, bacteria are the most suitable model organism because of their unique properties.
Bacteria or microbial culture which can grow on minimal media (only simple inorganic salts) are called as prototrophic. In contrast, the mutant bacterial culture which required all the essential nutrients like amino acids and organic salts, are called as auxotrophic.
Wild-type cultures are prototrophic while biochemical mutants are auxotrophic in nature Because biochemical mutant lacks in some metabolites which they required to grow. Hence they need all type of nutrients.
Auxotrophic mutants are unable to synthesize essential nutrients like amino acid, vitamins and nitrogenous bases whereas wild-type strains of bacteria can synthesize all the essential metabolites.
When nutrients and metabolites rich media are given to auxotrophic mutants, the condition has become permissive for them and mutant can grow.
Loss of function mutation
In simple terms, a mutation that causes functional retardation of the gene are called as loss of function mutation. Loss of function mutation depends on the condition of inheritance of that mutation. Generally, it remains recessive.
If the wild-type normal allele is dominant and expressed over mutant allele than even in heterozygous condition, the loss of function mutation remains recessive. It is also called a null mutation.
Mutant allele is expressed in a condition where both the recessive alleles (homozygous recessive) are overexpressed than normal wild-type allele.
Gain of function mutation
Loss of function mutations are most common in nature, but some mutation gives new function to a gene or gives original function back to a gene. However, this types of mutation are rare. Remember, sickle allele.
In sickle cell anaemia-heterozygous condition, individual remain unaffected but mutation gives one additional benefit from protecting against the malaria parasite.
Read next article: Mutation class 2: Different types of mutation
Temperature sensitive mutant
Mutant that is growing at one temperature and remain suppressed at another temperature, are called as a temperature-sensitive mutation. Most enzyme-coding genes are temperature sensitive, enzymes are activated at once specific temperature.
Mutation from wild-type to mutation or evolution of new mutation from wild-type is called as a forward mutation. Forward mutation leads to an evolution of new traits in the population. It is a natural phenomenon in nature.
Mutation is a unidirectional process, but sometimes some mutation gives original (wild-type) traits back to population, such mutation is called as the backward or back mutation. Back mutation is very rare and unusual process in nature.
It gives original phenotype back into the population by true back mutation or by the occurrence of a secondary mutation.
In true back mutation, a mutation occurred at the same location as it occurred during forward mutation. In simple words, it gives the wild-type codon back to population.
In secondary mutation, an occurrence of a new mutation in any place, in the sequence of the gene which gives the original function back or sometimes the new mutation suppressed the effect of the previous forward mutation.
Mutation in one gene influences more than one trait or phenotype is referred to as pleiotropy. Again recall the situation in sickle cell anaemia. Mutant HBS allele results in anaemic condition as well as protect the heterozygous individual from the malaria parasite. We will discuss pleiotropy broadly in other articles.
Article written by – Tushar Chauhan