This document discusses different types of mutations including gene mutations, chromosome mutations, and mutations caused by changes in ploidy level. It describes various chromosomal aberrations such as deletions, duplications, inversions, and translocations. It also discusses the causes of mutations, including radiation, chemicals, base analogs, and changes to DNA structure. Mutations can be induced artificially using mutagenic agents like radiation or chemicals to increase the mutation rate above spontaneous levels. Induced mutations have been observed in fish through X-irradiation and chemical treatment of gametes.
2. • An inheritable spontaneous deviation from the
“wild type” is called “mutation” and the organism
in which it occurs is called a “mutant”.
• Genetic recombination cannot create new alleles
in the first instance: the ultimate source of all
genetic variation is mutation.
3. • Mutations are caused by alterations in the
structure, arrangement or quantity of DNA.
Characteristically they are random (almost),
rare, recessive, and harmful.
4. Chromosome mutations
• Chromosome mutation may change the order of
the genes within the chromosome, e.g., by
deficiency, deletion, inversion, duplication, or
translocation. Gene or point mutations may result
from changes in the base sequence in a gene.
5. Mutations caused by changes to ploidy level
Changes in the number of chromosomes can
also cause mutation.
6. Aneuploidy
• Gain/loss of individual chromosome, from a set.
There are several reports of aneuploids in
salmonids.
• E.g., a male brook trout that was trisomic for a
chromosome carrying a LDH-B enzyme locus
was reported.
7. 1.Nullisomics
(2n-2)
- both of a pair of homologous
missing from a diploid set
2.Monosomics
(2n-1)
- one chromosome from a diploid
set missing.
3.Trisomics
(2n+1)
- one extra chromosome.
8. Chromosomal aberration
• Four main types of chromosome aberrations are
known.
• Deletion– Fragment of chromosome is missing
• Duplication – Fragment of chromosome
becomes duplicated.
9. • Inversion – Fragment detaches and reinserts
in the reverse order
• Translocation – A segment from one
chromosome becomes connected to a non
homologous chromosome.
10. Inversions can be classified into two main types.
• Paracentric inversions which do not involve the
centromeric regions are difficult to detect.
• They do apparently occur in fishes quite
frequently, but their presence can only be
established by analyzing the inheritance of the
linked genes.
11. Pericentric inversions
• Pericentric inversions involving the centromere
are quite frequent. If the two breakage events
take place at equal distances from the
centromere one cannot detect the inversion
without the analysis of marker genes.
•
• When the sites of breakage are located
asymmetrically, the relative length or even the
absolute number of chromosomal arms will be
changed.
12. Gene Mutations
• Gene mutations are broadly of the following
types.
• Substitutions.
• Tautomerism.
13. • A transition is an exchange of a purine with
another purine or a pyrimidine with another
pyrimidine.
• A transversion refers to the substitution of a
pyrimidine with a purine or vice versa.
• Tautomerism
Like many organic molecules, the bases may
change their shape (isomerism).
14. The following structural changes occur in DNA
• Pyrimidine dimers, in which two adjacent
pyrimidines on a DNA strand are coupled by
additional covalent bonds and thus lose their
ability to pair.
• Chemical changes of single bases, such as
alkylation or deamination, thus causing changes
in the pairing properties of the DNA.
15. • Crosslinks between the complementary DNA
strands, which prevent their separation in
replication.
• Intercalation of mutagenic agents into the DNA,
causing frameshift mutations.
• Single-strand breaks.
• Double-strand breaks
16. Induced Mutation
• Factors which cause mutations are called
mutagenic agents or mutagens. A mutagen, by
definition, is an agent which increases the
frequency of mutation.
• Mutation which occur at a frequency above the
base (spontaneous rate) are described as
induced.
17. The most well-known mutagens are
• high energy irradiations, and
• chemicals.
High energy irradiations
• These are the most frequent cause of mutation.
• Most of the natural mutations are caused by cosmic
rays from outer space and irradiations from radioactive
elements.
18. • Mutations may be artificially induced in
organisms by exposing them to X-rays, protons,
neutrons and alpha, beta and gamma rays from
radioactive sources such as radium, cobalt-60,
etc.
19. 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.
• Mutagens which affect nonreplicating DNA.
• Base analogs, which are incorporated into
replicating DNA due to their structural
similarity with one of the naturally occurring
bases.
20. Induced mutations in fish
• The frequency of mutations in fishes can be
markedly increased by X-rays and chemical
treatment
• X-irradiation of fish gametes results in the
appearance of various genic and chromosomal
mutations
• Chemical mutagens, particularly
nitrosoethylurea (NEU) are highly effective in
inducing mutations in fishes.