BOTANY Higher Secondary Second Year - Textbooks Online

3.5. Mutation
In a species, variations are caused by changes in the environment or
any changes in the innate genetic setup of an organism or by the combination
of both. Sudden change in the genetical set up of an organism is defined as
mutation. In 1901, Hugo de Vries first used the term mutation based on
his observation on Oenothera lamarckiana. Charles Darwin termed these
sudden change as ‘sports’. According to Bateson, mutation is a
discontinuous change. Based on molecular basis of heredity, mutation is
defined as sudden change in the sequence of nucleotides of gene. The
mutation brings about a change in the organism. The organism which
undergoes mutation, is called a mutant. eg. Oenothera lamarckiana.
Mutations that affect the biochemical reactions are called biochemical
mutations. For example, biochemical mutants of Neurospora failed to
synthesize certain amino acids. Some mutations drastically influence the
genes and cause death to the individual. Such mutation is described as
lethal mutation. For example, in the plant Sorghum, recessive mutant
fails to produce chlorophyll and therefore they die in the seedling stage.
Thus, most of the mutations are harmful, because they disturb the genic
balance of the organism. Although most of the mutations are useless and
even harmful, and some of the mutations play a significant role in the
evolution of new species. Many new strains of cultivated crops and new
breeds of domesticated animals are the products of gene mutations. Small
seeded Cicer arietinum (bengal gram) suddenly get mutated to large seeded
Cicer gigas is the case of gene mutation.
Classification of mutation
Mutations have been classified in various ways based on different
criteria. Depending on the kind of cell in which mutations occur, they are
classified into somatic and germinal mutation. They may be autosomal or
sex chromosomal according to their type of chromosome in which they
occur. They may be spontaneous or induced according to their mode of
origin. They may be forward or backward according to their direction.
They may be dominant or recessive according to their phenotypic
expression of mutated genes.
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