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USEFUL MUTANTS
 Heritable changes can result
in a useful novel phenotype,
i.e., a new allele.
Other Kinds
Some “not bad” Mutants
Sweet Corn
 Single gene mutations in several different starch
biosynthesis genes have been introduced into tender,
flavorful corn to produce the sweet corn we eat today Instead of transferring sugars into starch, they
accumulate ‘sweetness’.
 Shrunken (Supersweet), sugary, sugary enhancer,
amylose extender.
Ornamental Corn
Single gene mutations in the anthocyanin (pigment)
production pathway lead to the colored kernels we see
on an ear of Indian corn.
Waxy Corn
A mutation in the waxy gene is used in production of
tapioca and other gelling starch products.
High-lysine Corn
 A mutation in the opaque2 gene results in
increased levels of the essential amino
acid, lysine.
 Quality Protein Maize (QPM).
o2, opaque endosperm: endosperm soft and opaque; high lysine
content; regulates b-32 protein. Photo: seed from a selfed ear
segregating for opaque kernels in transmitted light showing
opaqueness of mutant kernels.
And of course - Disease resistance
 Insect resistance
 Glossy mutants
 Flowering time
 Cytoplasmic male sterility
 Nutritional changes
 “Value-added” changes
Mutations and Co-evolution
 Variations usually exist in nature.
 Co-existing species experience
mutual selection.
Domestication by Culture
 Suppression of ‘Wild’ Traits
 Seed scattering
 Mixed timing
 Hard-shelled seeds
 Mutation/Selection of ‘Desired’ Traits
 Packaging
 Convenience
 Storability
 Processing
Domestication in Wheat
 DIVERGENCE, CROSSING, SELECTION
 Earliest cultivated and wild wheat, with the 7chromosome A genome (left), crossed with
another, with the B genome, (third) about 8000 BC.
The result was durum wheat (emmer = PASTA
WHEAT), fourth in this photo. Emmer crossed with
wild goat grass (fifth) and gave rise to the staff of
life (BREAD WHEAT), sixth. The combination,
AABBDD, 7x3 = 21 chromosomes, is productive
and high in food quality.
Dwarf Wheat Opened Doors
 Ninetieth birthday of the Father of
the Green Revolution, Nobel Peace
Prize Laureate Norman Borlaug
http://www.cimmyt.org/english/webp/support/news/borlaug_90.htm
New Wheats a la Nature
 Deliberate employment of diversity in collections.
 Crosses of AABB with diverse DD and others.
Mutant Images for Maize
http://www.maizegdb.org/cgi-
bin/imagebrowser_phenotypes.cgi
Ramosa tassel and ear
Terminal ear1
Teopod2, Tunicate1
White pollen1 (bursting)
Virescent1
Directed Transposon Tagging
An example---cloning the male sterile silky1 (si1) gene using Mutator.
si1 y1/si1 y1 X Si1 Y1/Si1 Y1, Mu-active
(white seed/silky tassel) X (Yellow seed/normal tassel)
all Yellow seed (y1/Y1)
si1 y1/Si1 Y1 (99.99%) Normal Phenotype
si1 y1/si1-mum Y1 (rare mutant 1/10000)
X Si1 y1/Si1 y1
Yellow seed have tagged si1 allele (Si1 y1/si1-mum Y1)
Grow plants from yellow seed and backcross to si1 y1/si1 y1.
Plant out seeds, score for silky vs normal tassel phenotype.
Prepare DNA from leaves of each type.
Perform co-segregation analysis to identify
transposon linked to your mutant phenotype.
Southern Blot Hybridized with Mu1 Probe
(normal tassel)
(silky tassel (si1/si1-mum))
TILLING = Targeting Induced Limited Lesions IN Genomes
Make mutant population
EMS treat pollen
c1 Sh1 Bz1
Maize
Genetics
Stock Center
for
distribution
M2
bz1*
sh1*
Minimum
criteria: ≥50
M2 seed with
≥60%
germination
Bulk
Seed
DNA
C1 sh1 bz1
M0
M1
M3
Lyophilized
leaf disks
Random
intermating
Growouts
open to
the
general
public
Forward
screens
for
specific
traits of
interest
DNA prepared and equal amounts of
each sample arrayed to microtiter
wells, then these 8-fold pooled
IR-labeled primers create
double end-labeled
fragments
IR700
Bands of complementary
size are visible, one in
each image channel,
corresponding to singly
end-labeled fragments
cleaved by CELI at the
mutation site.
Mutant individuals
identified from pools,
sequenced. Information
and analysis returned to
200 bp
User, along with Stock
Center numbers for
ordering seed.
95bp
IR800