Maize Mutants - Text Only Version
DNA sequencing provides new tools for understanding crop
traits and for selecting desirable traits with greater efficiency.
The genes that govern many specific traits have been identified
in the genome of maize (corn) and located along the plants ten
chromosomes.
Just a few of these genes are included in this activity, yet they
demonstrate how broadly the gene sequences in DNA affect an organism's
appearance and health.
Below is a list of corn's ten chromosomes. Each chromosome contains
genes that govern specific physical traits of corn.
Chromosome 1
lls1 Gene - Lethal Leaf Spot
A gene mutation creates lethal lesions. The affected leaf is shown
on the left with a normal leaf on the right. Sunlight is required
to make leaf lesions appear. The plant looks diseased, but no disease
organism is present.
p1 Gene - Pericarp Color
The gene governs red pigment in the cob and outer casing of the
kernels (pericarp). Variations are shown. The red candy stripe
ears of corn sold in stores at Thanksgiving have a variation of
this gene.
zb7 Gene - Zebra Crossbands
A gene mutation creates glossy seedlings with light green crossbands.
The crossbands are due to cooler temperatures at night.
tb1 Gene - Teosinte Branched
One of the genes involved in the transformation of ancient teosinte
into corn; a variation creates the extra stems and tassel like
ear branches seen in teosinte.
Chromosome 2
mnl Gene - Miniature Seed
A gene mutation that creates small but structurally and functionally
complete kernels vs. variable kernels are shown. The gene governs
an enzyme involved in breaking sucrose down into glucose and fructose.
w3 Gene - White
The gene variation causes white seedlings. A normal seedling is
shown behind and to the right. The gene blocks a chemical pathway
that gives yellow and orange color to fruits and vegetables.
ch1 Gene - Chocolate Pericarp
The gene variation creates chocolate-colored kernel shells (pericarp)
Chromosome 3
cg1 Gene - Corngrass
A variation in this gene causes plants to have narrow leaves and
extra stems. This mutant is often mistaken for a grassy weed in
corn genetic nurseries.
vg1 Gene - Ragged Leaves
Plants with this mutation have defective tissues between veins
of older leaves, causing holes and tearing.
a3 Gene - Anthrocyanin
A gene mutation creates intense purple pigmentation in leaves
and other plant parts. Normal plants are green. The gene controls
other genes and does not itself produce the pigment.
Chromosome 4
la1 Gene - Lazy Plant
A gene variation causes the plant to grow horizontally; it will
break if straightened up.
su1 Gene - Sugary
A wrinkled, translucent kernels are sweet at the milky stage;
dry, collapsed, angular, and brittle at mature stage. Most sweetcorn
is sweet because of this gene.
tu1 Gene - Tunicate
Kernels are enclosed in long glumes and tassel glumes are large
and coarse in Tu1 plants. A common name is "pod" corn.
Roundup Ready Gene - Herbicide Resistance
This inserted gene makes crops more resistant to broad-spectrum
herbicides, reducing the quantity of various herbicides used.Roundup
Ready corn treated with herbicides is shown on the left, untreated
on the right.
Chromosome 5
bm1 Gene - Brown Midrib
The gene mutation causes brown pigment over the midsections of
the leaf. A normal, green leaf is shown at right. The gene affects
the composition of lignin, a cell wall constituent.
bt1 Gene - Brittle Endosperm
A gene mutation causes mature kernels to collapse and become brittle.
The gene affects an enzyme bound to starch granules.
ys1 Gene - Yellow Stripe
A gene mutation causes an iron deficiency that leads to yellow
tissues between leaf veins.
Chromosome 6
po1 Gene - Polymitotic
Sterile pollen in tassels result from a mutation on this gene.
A normal male tassel is shown on the left; the po1 tassel on the
right. This gene causes extra divisions in pollen that result in
cells with varying numbers of chromosomes. The cells abort, which
leads to sterility.
si1 Gene - Silky
Multiple silks in ears and sterile tassels result from a mutation
of this gene.
sm1 Gene - Salmon Silks
The gene governs color variations in the ear silks. Bright salmon-colored
silks are shown.
Chromosome 7
vs1 Gene - Rough Sheath
Plants with this mutation have rough sheaths and extreme disorganization
where leaves separate from stems.
ij1 Gene - Lojap Striping
A mutation in this gene causes many variable white stripes, which
can be seen on leaf margins.
Bt Gene - Pest Resistance
Bt crops are "transgenic" - they have been genetically
engineered to increase resistance to pests and reduce the need
for pesticides. The gene's location among the chromosomes varies
from one strain to another. The Bt field is on the right in this
comparison.
Chromosome 8
v16 Gene - Virescent
This gene mutation causes pale yellow seedlings that green rapidly
to normal. The v16 seedling is shown on the left, with a normal
seedling on the right. The yellow color of seedlings is a temperature
effect that occurs when the ambient temperature is below 64º -
68ºF(18º - 20ºC).
j1 Gene - Japonica Striping
White stripes on the leaves are caused by a mutation in this gene.
This gene has been used to study how leaves develop.
Chromosome 9
Dt1 Gene - Dotted
This gene variation causes colored dots on colorless kernels and
purple sections on brown plants.
bz1 Gene - Bronze
The pale bronze kernels result from this gene mutation. Many features
of maize genetics have been revealed using this gene.
Chromosome 10
cr4 Gene - Crinkly Leaf
The gene mutation leads to crinkly leafed seedlings and short
plants. This trait is expressed in developing shoots, but not in
mature leaves.
r1 Gene - Colored Variations in this gene sequence yield red or purple
colors. The gene regulates pigment production in seed and plant.
This gene has been used extensively to study gene structure, gene
interactions, and gene expressions.
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