organism. Mutations are classified into two main types, namely chromosomal mutation and gene mutation. . Chromosomal mutation The sudden change in the structure or number of chromosomes is called chromosomal mutation.
This may result in (i) Changes in the structure of chromosomes: Structural changes in the chromosomes usually occurs due to errors in cell division. Changes in the number and arrangement of genes takes place as a result of deletion, duplication, inversion and translocation in chromosomes. (ii) Changes in the number of chromosomes: They involve addition or deletion in the number of chromosomes present in a cell. This is called ploidy .
There are two types of ploidy (a) Euploidy (b) Aneuploidy. Euploidy: It is the condition in which the individual bears more than the usual number of diploid (2n) chromosomes. If an individual has three haploid sets of chromosomes, the condition is called triploidy (3n). Triploid plants and animals are typically sterile.If it has four haploid sets of chromosomes, the condition is called tetraploidy (4n).
Tetraploid plants are advantageous as they often result in increased fruit and flower size. Figure . Euploidy Triploid Oyster Diploid Oyster Aneuploidy: It is the loss or gain of one or more chromosomes in a set. It is of three types.
Monosomy (2n- ), Trisomy (2n+ )and Nullisomy (2n- ). In man, Down’s syndrome is one of the commonly known aneuploid condition. Down’s syndrome This condition was first identified by a doctor named Langdon Down in1866. It is a genetic condition in which there is an extra copy of chromosome (Trisomy ) .
It is associated with mental retardation, delayed development, behavioural problems, weak muscle tone, vision and hearing disability are some of the conditions seen in these children. Figure . Aneuploidy . Gene or point mutation Gene mutation is the changes occurring in nucleotide sequence of a gene .
It involves substitution, deletion, insertion or inversion of a single or more than one nitrogenous base. Gene alteration results in abnormal protein formation in an organism. S ickle cell anaemia is caused by the mutation of a single gene.