Plants defy Mendel's inheritance laws, may prompt textbook changes

[C1ay]

Contrary to inheritance laws the scientific world has accepted for more than 100 years, some plants revert to normal traits carried by their grandparents, bypassing genetic abnormalities carried by both parents.

 

lefthttp://www.hypography.com/gallery/files/9/9/8/pruittmutantLO_thumb.jpg[/img]These mutant parent plants apparently have hidden templates containing genetic information from the preceding generation that can be transferred to their offspring, even though the traits aren't evident in the parents, according to Purdue University researchers. This discovery flies in the face of the scientific laws of inheritance first described by Gregor Mendel in the mid-1800s and still taught in classrooms around the world today.

 

"This means that inheritance can happen more flexibly than we thought in the past," said Robert Pruitt, a Purdue Department of Botany and Plant Pathology molecular geneticist. "While Mendel's laws that we learned in high school still are fundamentally correct, they're not absolute.

 

"If the inheritance mechanism we found in the research plant Arabidopsis exists in animals, too, it's possible that it will be an avenue for gene therapy to treat or cure diseases in both plants and animals."

 

The study is published in the March 24 issue of the journal Nature.

 

Pruitt and collaborator Susan Lolle found that Arabidopsis in which each parent plant had two copies of a mutant gene could produce progeny that didn't show the parents' deformity, but rather were normal like the grandparents. Under Mendelian laws, the offspring should have shown the same mutation.

 

The first clue that the classic inheritance rules didn't always apply was the discovery of normal flowers on some offspring of mutant plants. In the deformed parents, the flowers were fused into tight balls. But in the grandparents and 10 percent of the grandchildren, the buds become 1-millimeter-long, bright white flowers that fully opened and radiated out from the center of a cluster.

 

"If you take this mutant Arabidopsis, which has two copies of the altered gene, let it seed and then plant the seeds, 90 percent of the offspring will look like the parent, but 10 percent will look like the normal grandparents," Pruitt said. "Our genetic training tells us that's just not possible. This challenges everything we believe.

 

"We've done a lot of experiments, described in this paper, that show none of the simple explanations account for this skipping of generations by an inherited trait."

 

The scientists kept the plants in isolation so they couldn't accidentally crossbreed with plants that didn't have the mutated gene, called hothead, that causes organ fusion like that seen in the flowers. The researchers used molecular markers - bits of DNA that help identify and locate genes in organisms - to determine whether a plant carried normal or mutant copies of the genes.

 

"It seems that these hothead-containing plants keep a cryptic copy of everything that was in the previous generation, even though it doesn't show up in the DNA, it's not in the chromosome," Pruitt said. "Some other type of gene sequence information that we don't really understand yet is modifying the inherited traits."

 

Although the hothead gene tipped the researchers off to this unconventional inheritance cycle, Pruitt believes that this particular DNA sequence is just a trigger for the phenomenon. He suspects that a number of other genes and the proteins they produce are involved in activating this process.

 

"We need to understand more about the molecular mechanics of how this process works," Pruitt said. "Then we will know exactly what role this gene plays."

 

Pruitt's team already knows that animals don't have hothead genes, either normal or mutated, so the scientists must investigate which genes might affect this novel inheritance in both plants and animals.

 

"There are probably a lot of other triggers yet to be discovered, and this mechanism for inheritance may require a different trigger to make it work in animals," he said.

 

Once scientists understand more about the mechanism, they then may be able to manipulate it to modify genes already in plants and animals in order to correct mutations that cause diseases and abnormal growth.

 

Though further research is required to learn how this form of inheritance happens and how it can help improve plants or animals through gene therapy, Pruitt said the discovery has opened an important new line of thinking.

 

The other researchers involved with this study were Jennifer Victor, a former Purdue graduate student now at Butler University; and Jessica Young, a botany and plant pathology laboratory technician. Lolle, a Purdue research scientist, is currently at the National Science Foundation.

 

The National Science Foundation provided funding for this research.

 

Source: Robert Pruitt, Purdue University

[Tormod]

Great article. Nature has a lot of surprises for us still.

[Will]

Great article. Nature has a lot of surprises for us still.

 

agreed. this is really cool. might explain why i look more like my grandparents than either of my parents :)

[Queso]

as far as i know they've known this is possible for humans......right?

[TeleMad]

as far as i know they've known this is possible for humans......right?

 

The typical "it can skip a generation" can, but this is something new. Here's the normal one.

 

Let's use the commonly used trait brown eyes vs. blue eyes (even though as usually presented, which will be copied here, is not accurate in all respects). The dominant Brown allele will be a capital B and the recessive blue allele with be lowercase b. So to be blue-eyed one must be homozygous recessive, bb: that means, his/her two alleles must both be recessive (if s/he had even one dominant allele, it would override the recessive).

 

Suppose the grandparents had brown and blue eyes, of the genotypes BB and bb. When they mate the only possible outcome is Bb. So 100% of the offspring, which includes one of your parents, will be Bb, Brown eyed. Now suppose that parent marries another Brown-eyed person of the same genotype, Bb. BOTH PARENTS ARE BROWN EYED. The possible outcomes for their offspring are BB (1), Bb (2), and bb(1). The first two genotypes, BB and Bb, of which there is a total of 3, produce brown eyes; while only 1, bb, produces blue eyes. So there is a 1 in 4 chance that if those parents had a single child that it will be blue-eyed: bb. If they have several children, they will likely end up with one that is blue-eyed, even though both parents were brown-eyed. So the recessive blue-eyed trait would skip a generation. It's in the grandparents, disappears in the parents, and returns in the grandchildren.

 

If we stick to the normal complete dominance mode of inheritance, as used above, then what the new article is saying that the individuals of the middle generation are bb, not Bb. So how do 2 bb parents produce a BB or a Bb offspring? There's no B for them to give to their offspring.

[BlameTheEx]

We could imagine a plant (or animal) keeping alternative copies of critical sections of DNA in what appears to be switched off genes. These would be time capsules. The idea would be to increase genetic diversity by including traits that were once useful and expressing them in a limited number of progeny on the offchance that they may be useful once again.

 

How would they be splice into the correct position? The plant may have some mechanism, or perhaps the plant does it the same way that we are trying - via a virus. It is just about possible that mother nature invented gene therapy before we did.

[Michaelangelica]

I told ya.

 

Please post on 'Darwin revisited' thread

 

Genes and DNA seem to get the ball rolling but then the environment and proximity to other genetic material also seems to come into play.

 

An then there are the protein coding bits. . .

 

the "junk DNA". . .

 

and 'what we know we don't know'. . .