question_answer

What is mutation? Give the names of some mutagens. How mutations are significant in agriculture?

OR

In man four types of blood groups A, B, AB and O are controlled by three alleles of a gene. What is the mechanism of inheritance of the blood group?

Answer:

Mutations are sudden inheritable changes which results in alteration of DNA sequences and changes the genotype and phenotype of an organism. Mutation leads to variation. The loss (deletion) or gain (insertion/duplication) of a DNA segment result in alteration in chromosomes which leads to abberations or abnormalities. Mutations also arise due to change in single base pair of DNA known as point mutation. Mutation was discovered by Hugo de Vries (1901).
There are various chemical and physical factors that can induce mutations. These are called mutagens. Physical mutagens include temperature and radiations. \[\alpha ,\,\,\beta ,\,\,\gamma \] rays, X-rays, ultra violet rays cause mutations in organisms. Some chemical mutagens are nitrous acid, alkylating agents, acridine dyes.
Mutations have played a significant role in agriculture by crop improvement. Plant breeders use mutations for improvement of plants for higher yield, nutritive value, disease resistance etc. Sharbati Sonora, a wheat variety was developed through mutations.
A high yielding rice variety called Reimei was produced by gamma irradiation. Cauliflower and cabbage are mutants developed from wild cabbage. Mutations are induced in plants to enhance their beauty and fragrance, e.g., Dahlia, Rosa. Many crop plants like wheat, rice, maize, gram, cotton, potato, sugarcane, banana developed by mutations in nature. In vegetative propagated plants, mutations are the only source of improvement and development of variability. Seedless varities of grapes and oranges are successfully produced through mutations.
OR
More than two allelic forms exist for certain genes. A well-known example is the A, B, O blood types in humans. The four human blood groups A, B, AB and O are the four phenotypes for this trait. These blood groups are controlled by the gene 'I'. The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar polymer is controlled by the gene 'I'. The gene I has three alleles \[{{I}^{A}},\,\,{{I}^{B}}\] and 'i'. Allele \[{{I}^{A}}\] determines the formation of sugar polymer-A and alleles \[{{I}^{B}}\] the formation of sugar polymer-B, while allele does not produce any sugar. Any person carried only two of these alleles, one from each parent. However, with three alleles, it is possible to obtain six genotypes combinations. They are shows below:
Phenotype (Blood Groups)	Genotype
O	\[ii\]
A	\[{{I}^{A}}{{I}^{A}}\,or\,{{I}^{A}}i\]
B	\[{{I}^{B}}{{I}^{B}}\,or\,{{I}^{B}}i\]
AB	\[{{I}^{A}}\,{{I}^{B}}\]
Both \[{{I}^{A}}\] and \[{{I}^{B}}\] are dominant over \['i'\]since a person with genotype \[{{I}^{A}}{{I}^{B}}\] produces both sugar polymers. They do not she dominant - recessive phenomenon with each other, hence, allele \[{{I}^{A}}\] and \[{{I}^{B}}\] are said to be co-dominant. They are both expressai in the phenotype as AB. The ABO system of blood groups is, therefore, an example of both multiple alleles and co-dominanc-1 types of inheritance mechanism.