Principles of Genetics and Breeding

6.1.4.2 Chemical mutations

A variety of chemicals are known which are mutagenic, and these may be classified into three groups according to their modes of action.

1. Mutagens which affect nonreplicating DNA.
2. Base analogs, which are incorporated into replicating DNA due to their structural similarity with one of the naturally occurring bases.
3. Frame shift mutagens,which enter into DNA during replication or repair and through this intercalation cause insertion or deletion of one or a few nucleotide pairs.

Nitrous acid- Promotes deamination and mispairing.

Base analogues- resemble normal bases, but cause mispairing.

• No data are as yet available on the frequency of gene mutations in fishes, but this frequency appears not to be high.
• For example, after the examination of 260 thousand individuals of the common carp,no single mutation affecting the S and N genes responsible for the pattern of scales had been found.
• The populations of many fish species appear to be saturated by mutant forms of genes coding for the synthesis of many different proteins.