1. Mutation and Mutation Breeding

2. Mutation Sudden change in the hereditary material of a cell Can be:
Chromosomal
Genic
Molecular level
Mostly
Deleterious
Harmful
Lethal

3. Mutation New genetic variability – new adaptation
An organism that exhibits a novel phenotype resulting from a mutation = mutant

4. b c a Mutation (a) Variegated plant
Each green cell has a mixture of normal chloroplast and plastids with a mutation that prevents chlorophyll synthesis. Cells in the white area have only mutant plastids. b
(b)
Cells usually have many plastids and mitochondria, so random distribution of the organelles is usually sufficient to ensure both cells receive some. c a
(c)
If mutant plastids are present, then occasionally when cytokinesis occur, one end of the cell may have only mutant plastids.

5. Type of mutation Micromutation / point mutation/ microlessions
Macromutation/ Chromosomal aberrations

6. Miromutations or Point mutations
Small effects on the organisms
Change in one base
Types:
Base substitutions
Transition = Pyrimidine to Pyrimidine or A-G
= Purine to Purine T-C
Transversion = Purine to Pyrimidine or
= Pyrimidine to Purine
Base insertion
Base deletion
Frameshift

9. Maromutations Big effect on the organism Involved big chunk of DNA
Types
Inversions - Fliped
Deletion - Lossed
Duplication - Duplicated
Translocation - Moved

11. Chimera
When mutations occur in somatic tissue, only a small sector of the plant will carry the mutant gene.
In this case, that small sector of the plant is called chimera.

12. Chimera

13. Chimera
Tunica-corpus model

14. Chimera Mutated cell do not entirely cover the apical dome.
Involve limited number of cells.
Generally, one cell layer.
Giving rise to chimeral and nonchimeral shoots.

15. Chimera Relatively stable and can be vegetatively propagated.
Mutated cell is positioned near the apical dome.
Meristem contains one layer which is genetically different from the remainder of the meristem.

16. Chimera mutations affect sections of the apical meristem
Altered genotype extending through all the cell layers.
Giving rise to chimeral and nonchimeral shoots.

17. Recessive Vs. Dominant mutation
Recessive mutation
Change from a dominant allele to recessive allele
Common
Dominant mutation
Change from a recessive allele to dominant allele
rare

18. Recessive mutation M1 generation M2 generation Mutagen selfed AA
No mutation AA AA
Seeds or
Plants AA AA Aa
Mutation – Chimeric
1AA:2Aa:1aa
Mutation –
Non-chimeric Aa

19. Recessive mutation Chimeric plant
Mutagen treatment of wheat seeds induces a recessive mutation in an embryo meristemic cell.
A tiller (M1) that arises from that affected
cell is heterozygous for the mutant gene.
When M1s are selfed, the M2s from the
affected tiller will show 3:1 segregation
ratio. One out of four M2 plants will
exhibit the recessive mutant character and seeds from this tiller will produce mutant plants in the M3.
From the same M2 population, two plants
out of four are heterozygous. The recessive mutant will segregate out in the M3 generation.
Heterozygous
3:1
1-AA
2-Aa
1-aa

20. Dominant mutation M1 generation M2 generation Mutagen selfed aa
No mutation aa aa
Seeds or
Plants aa aa Aa
Mutation - Chimeric
1AA:2Aa:1aa
Mutation –
Non-chimeric Aa

21. Germinal mutation Occur in germline cells
Occur at any stage in the reproductive cycle of the organism
Dominant mutation which occur in germline cells – effects is expressed immediately in progeny

22. Somatic mutation Occur in somatic cells
Resulting mutant phenotype occur only in the descendants of that cells
Mutation will not be transmitted to the progeny
Only through vegetative propagation the mutant can be maintained and perpetuated

23. Somatic mutation
In ‘Red delicious’, a mutant allele determining the colour of the ovary wall to be golden arose in a flower. This developed into golden apple.
As vegetative propagation is feasible for apple, this mutant was developed into a variety called the ‘Golden delicious’ variety – from muntant branch

24. Spontaneous Vs. Induced mutations
Spontaneous mutation
Occur in nature or without a known cause. Associated with natural forces. Result from normal chemical processes in the cell.
Induced mutation
Occurs as the result of the influence of any artificial factor, i.e. physical and chemical agents that cause changes in DNA.

25. Mutagens Ionizing radiations X-rays Neutrons Gamma ray Ultraviolet
Laser beam
Chemicals
EMS (Ethyl methanesulfonate)
dES (Diethyl methanesulfonate)
EI (Ethyl Imine)

26. Ionizing radiation X-ray Widely available Easily operated
Seeds, plants or pollen can be treated with fairly accurate doses.
Neutron radiation
Produces more severe damage to the chromosome than X-ray.
It is used mainly with seeds.

27. Ionizing radiation Gamma rays
Emitted from radioactive cobalt or radioactive isotopes
Cause less injury to the plant cells
Frequently used for whole plants or plant parts including pollen.
Laser beams is a more recent event.

28. Ionizing radiation The radiation dose is determined by:
Intensity of the radiations
length of the exposure.
IAEA (International Atomic Energy Agency) in Vienna provides training course and publishes manuals on the use of ionizing radiation in mutation breeding.

29. Chemical mutagens Simpler to use and produce less damaging effects.
The most widely used is EMS. It is a powerful carcinogen and must be used with extreme caution.
Seeds, buds, roots and dormant cuttings can be treated by soaking in a solution of the chemical mutagen.
Chemical mutagens are less drastic in their effects then ionizing radiations, producing more gene mutations and fewer chromosome disruptions.
However, it is not possible to direct the mutation process so that a specific type of mutation can be produced.

30. Use of mutagens What dose should be used?
Use the dose that kill 50% of the plants
Too high – Kill too many plants
Mutagens harmful to plants
Mutations are lethal
Too low – Not enough mutations

31. Tissue for mutagen treatment
Seeds
- easy to treat large number and easy to handle
- multicellular, M1 plants chimeric
Gametes or zygotes
- leads to non-chimeric heterozygous M1 plants
Vegetative propagules
- shoot meristem, adventitious bud
Cell and Callus cullture
- leads to non-chimeric regenerated plants

32. Example of mutations breeding
Sorghum – Example of spontaneous mutation
A dwarfed mutant plant was found in a farmer’s field.
Seeds increased and gave rise to the ‘Dwarf’ cultivar.
A second dwarfed mutant was found among the population of ‘Dwarf’ cultivar and a new cultivar called ‘Double dwarf ’ was developed.
Mutant dwarf form facilitate mechanized harvesting of the grain sorghum crop.

33. Plant cultivars from induced mutation
According to 1363 (FAO/IAEA, 1991)
Novel plant architecture
Earlier or later flowering time
Different flower colour or shape
Different fruit colour or size
Resistance to pathogens and pests
Changes in chemical composition, e.g. oil, fatty acid, protein, amino acid, starch quality etc.
Changes in reproductive characters e.g. male sterility, fertility restoration, self-incompatibility, seedlessness