Putting DNA to Work
  IMPROVING CROPS

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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