The news is fascinating and relevant, but I just wanted to make sure =
novice folks (like me! :^> ) know it's not like 5 lucky gamma ray hits =
are going to do this. Right?
Was there any report on how different the genes were, base-pair-wise?
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From: Glenn Morton[SMTP:GRMorton@gnn.com]
Sent: Wednesday, June 19, 1996 2:33 PM
To: evolution@Calvin.EDU
Subject: rapid evolution
This is a few paragraphs from an article in the Dallas Morning News last =
Monday. It seems that the quantity of mutations to make rapid=20
morphological change is quite small. In the case of the evolution of=20
teosinte into corn, 5 mutations are all that was required. The teosinte =
plant was at one time classified in an entirely different genus from =
corn.
"Even though corn looks different from other plants, it's not that=20
far removed from its predecessor, teosinte. Experiments reported in the=20
1970's by geneticist George Beadle suggested that changes in as few as=20
five of the plant's thousands of genes are responsible for the major=20
differences between teosinte and maize. Dr. Doebley has confirmed the=20
results.
"One of the genes, abbreviated tga, makes it easy to eat the =
kernels.=20
In teosinte, the tga gene directs the plant to form a casing around =
teach
kernel. This fruit case makes the kernel hard to get to. But in modern =
corn, the tga gene has a different form, one that stops the fruit case=20
from completely enclosing the kernel. Without the genetic change, corn=20
kernels would be really tough to sink your teeth into, Dr. Doebley said.
"And corn would be tough to harvest, too if it weren't for a gene=20
called tb1. In teosinte, the gene causes the plant to have many stalks, =
which means there are a lot of ears on each plant.
"'Although that may sound good for farming, it really isn't.' Dr.
Doebley said. To understand why, he said, think of the sunflowers that=20
have one big flower at the top and those that have several smaller=20
flowers.
"Say you'd like to get a thousand sunflower seeds,' he said. 'Would =
you rather pick one head and get a thousand seeds, or 10 heads with a=20
hundred seeds?'
And even though the 10 flowers are all on the same plant, they are
likely to go to seed at different times, so a farmer would have to go =
back=20
to the plant more than once.
"Dr. Doebley and his co-workers have isolated the tb1 gene and=20
compared the teosinte version with the corn version. Preliminary=20
experiments suggest that the gene's job is to prevent side branches from =
growing too big. In teosinte, the long branches grow. But in corn, it=20
turns out, the gene is more active causing fewer, shorter branches. The =
result is that corn plants, depending on the variety, have only two to=20
five ears. Teosinte can have a dozen.
"The corn version of the third gene causes the ear to have more=20
kernels, and influences branch length and the arrangement of the =
branches=20
on the main stalk. The fourth gene also affects the branching pattern,=20
and the fifth seems to modify many different traits."~Sue Goetinck,=20
"Geneticists working to Learn How Ancient Plants Became Grains that Feed =
the World," Dallas Morning News, Monday, June 17, 1996, p 6D, 7D.
glenn
Foundation,Fall and Flood
http://members.gnn.com/GRMorton/dmd.htm