12- 4 Mutations

Mutation Changes in the genetic material The cell makes mistakes in copying their own DNA, inserting or skipping a base.

Kinds of Mutations Mutations that produce changes in a single gene are – Gene Mutation Mutations that produce changes in whole chromosomes are -- chromosomal mutations.

Gene Mutation Point Mutation – Changes in one or few nucleotides, because they occur at a single point in the DNA sequence. In includes substitution – one base is changed to another, insertion – One base is inserted deletions – It removes a DNA sequence.

Substitution usually affects no more than a single amino acid.

The effects of insertion or deletions can be much more dramatic. Genetic code reads in three- base codons. If there is still read a codon at a time but there groups are shifted for every codon that follows.

Frameshift mutations They shift the reading frame of the genetic messeges. It can cause the change of every amino acid that follows this mutation. It can alter a protein so much that it is unable to perform its normal function.

Deletion

Gene Mutation Insertion Point Mutation Substitution Frameshift Mutation Deletion

Chromosomal Mutations It involves changes in the number or structure of chromosomes. It can cause a change in the location of genes on chromosomes Change the number of copies of some genes.

Deletion The loss of all or parts of a chromosome.

Duplication Produces extra copies of part of a chromosome.

Inversion Reverse the direction of parts of chromosomes

Translocation Part of the chromosome breaks off and attaches to another.

Significance of Mutations Most of the mutations are neutral, that have no effect on the expression of genes or the function of the protein for which they code.

Mutations that cause dramatic changes in protein structure or gene activity are often harmful, that disrupt normal biological activity.

Mutations are source of genetic variability in species; and some may be beneficial.

Mutations can cause genetic disorders. Can cause cancer Beneficial mutations may produce new proteins that are useful to organisms in different or changing environment.

Plant and Animal Breeders Take advantage of such beneficial mutations. When a complete set of chromosomes fails to separate during meiosis, the gamets that result may produce triploid(3N) or tetraploid (4N) organisms. Organisms that have an extra sets of chromosomes is polyploidy.

Polyploidy plants are often larger and stronger than diploid plants Polyploidy plants are often larger and stronger than diploid plants. Crop plants, bananas and citrus fruit have been produce in this way.