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Why does F1 Hybrid Vigour occur ?

C

cryptolab

New member
Hello Denizens,

I find this whole topic of F1 Hybrid Vigour, particularly interesting.
I understand what F1 Hybrid Vigour is, as a description of its effect.
And I understand under what circumstances it will happen.
What i don't understand, is 'why' ?

Why does F1 Hybrid Vigour occur ?

The picture below, pretty much sums up the effect:

PiHFM55.jpg



I'm sure many of you have spent plenty of time studying and working
on issues relating to plant breeding and hybridization... Perhaps you
can offer a perspective on this issue that sheds light and understanding
on the whole topic.

Thanks to those who offer a reply

have a nice day

cryptolab :)
 
B

Betterhaff

Well-known member
Veteran
I don’t think it’s totally understood as to the actual reason why. Many theories though. Some say the dominance thru dominant heterozygous loci, and their abundance thru inheritance from different parents suppresses the effects of homozygous recessive loci that may be present in each parent.
 
Gypsy Nirvana

Gypsy Nirvana

Recalcitrant Reprobate -
Administrator
Veteran
Hybrid vigor works, but no one understands how. ISU plant scientists have uncovered a key to understanding the complex molecular mechanisms of this biological process. Their findings were published in the May 2 edition of the Proceedings of the National Academy of Science.

For nearly 80 years, corn breeders and producers have taken advantage of hybrid vigor to grow high-yielding crops. Yet this biological process remains a scientific mystery. No one really understands why crossing specific lines of corn that are genetically quite different can produce a hybrid that outperforms both parent lines.

That could change, however, thanks to ongoing research in Iowa State University's Plant Sciences Institute. Researchers have uncovered a key to understanding the complex molecular mechanisms of hybrid vigor, also known as heterosis, which affects most aspects of plant growth and development. Once the gene activity behind hybrid vigor is well understood, scientists could more rapidly create hybrids that confer desired traits like ethanol production into the germplasm.

The research team, led by Patrick Schnable, professor of agronomy and director of the Center for Plant Genomics, includes Dan Nettleton, associate professor of statistics; and graduate students Ruth Swanson-Wagner, Yi Jia, Rhonda DeCook and Lisa Borsuk.

Their research is published in the May 2 issue of the scientific journal, Proceedings of the National Academy of Science ("All Possible Modes of Gene Action are Observed in a Global Comparison of Gene Expression in a Maize F1 Hybrid and Its Parents").

For the two-year experiment, the researchers used the maize F1 hybrid and its inbred parents corn lines, B73 and Mo17. The F1 is taller, matures more quickly and produces higher grain yields than both parents.

"We analyzed global patterns of gene expression in these three genotypes because this hybrid and its relatives are widely grown in the Corn Belt," Schnable said. "Also, the genetic map of corn is based on recombinant inbreds developed from this hybrid."

The researchers grew seedlings of the three genotypes in growth chambers to tightly control environmental effects. They isolated RNA from each of the three genotypes, and used a maize gene chip to determine the amount of RNA that accumulates for each gene in each of the three genotypes.

"We used this gene expression information to understand how each of thousands of genes behave in the genetic background, " Schnable said.

Using microarray technology, the researchers observed the activity of nearly 14,000 genes at the same time. The technology enabled them to look simultaneously at the gene expression of the hybrid and its inbred parents. This is the first study that has looked at hybrid vigor in any crop on such a large scale.

They found that some genes are more active in the hybrid than in both of the parental inbred lines (overdominant), some genes are less active than both inbred lines (underdominant) and most genes --78 percent -- have activity levels in between the level of the inbreds (additive).

"Several molecular models have been proposed to explain the phenomena of hybrid vigor. Some models require that genes exhibit overdominance or underdominance. Others assume that overdominant and underdominant gene expression is not an important contributor to hybrid vigor," Schnable said.

The results of the Iowa State experiment provide support for multiple mechanistic explanations for hybrid vigor.

"Although this research does not explain hybrid vigor, it begins to uncover what happens on a molecular level in a hybrid compared to the inbred parents. It shows us that there are multiple molecular mechanisms at work and that hybrid vigor is complex," Schnable said.

"To understand this important biological process, we will need to apply cutting-edge, high-throughput genomic technologies. The Plant Sciences Institute at Iowa State is one of very few public-sector organizations in the world that has the technology and resources necessary to conduct this research," he said.

The research findings provide a foundation for the Iowa State scientists to explore specific genes of interest, or investigate the contributions of the different mechanisms resulting in the gene expression patterns found. Their next step is to determine the genetic control of overdominance.

"Ultimately, it is likely that we would be able to predict which specific inbreds when crossed would produce a strong heterotic response. To a large extent, this is now a matter of trial and error. Consequently, we might be able to develop favorable hybrids more quickly for less cost. This would result in faster genetic gain," Schnable said.

Source: Iowa State University 2006


Read more at: https://phys.org/news/2006-05-mystery-hybrid-vigor.html#jCp
 
Fuel

Fuel

Well-known member
Veteran
Betterhaff said:
I don’t think it’s totally understood as to the actual reason why. Many theories though. Some say the dominance thru dominant heterozygous loci, and their abundance thru inheritance from different parents suppresses the effects of homozygous recessive loci that may be present in each parent.
Click to expand...

It's simply why the lost art of rotative crosses (3way, 4way etc) keep the heterosis momentum so long without losing accuracy.

If it was just a theory, the liter of milk will be as expensive that wine lol
 
B

Betterhaff

Well-known member
Veteran
Fuel said:
It's simply why the lost art of rotative crosses (3way, 4way etc) keep the heterosis momentum so long without losing accuracy.

If it was just a theory, the liter of milk will be as expensive that wine lol
Click to expand...
??...as I said, “I don’t think it’s totally understood as to the actual reason why. Many theories though.” I probably should have said, the underlying mechanisms are not totally understood.

“Hybrid vigor works, but no one understands how.” As stated in the article Gypsy posted.

It’s been known for quite some time that by crossing unrelated inbred lines, it can result in a hybrid with hybrid vigor but why it happens, the mechanisms that cause it, are not yet understood. I do believe that is the OP’s question.

Here’s a paper, a joint collaboration that includes Iowa State University (again). They know corn. The Conclusions section is interesting.

https://www.plantbreeding.iastate.edu/pdf/icb98.pdf
 
Fuel

Fuel

Well-known member
Veteran
I was talking about your comment on homozygous recessive loci only; i'm not really the type of guy that need to known how to build a car to drive it. I can deal with it ^^
 
C

cryptolab

New member
Betterhaff said:
I don’t think it’s totally understood as to the actual reason why. Many theories though. Some say the dominance thru dominant heterozygous loci, and their abundance thru inheritance from different parents suppresses the effects of homozygous recessive loci that may be present in each parent.
Click to expand...


Hey Betterhaff,

A+ :)
 
C

cryptolab

New member
Gypsy Nirvana said:
Hybrid vigor works, but no one understands how. ISU plant scientists have uncovered a key to understanding the complex molecular mechanisms of this biological process. Their findings were published in the May 2 edition of the Proceedings of the National Academy of Science.

For nearly 80 years, corn breeders and producers have taken advantage of hybrid vigor to grow high-yielding crops. Yet this biological process remains a scientific mystery. No one really understands why crossing specific lines of corn that are genetically quite different can produce a hybrid that outperforms both parent lines.

That could change, however, thanks to ongoing research in Iowa State University's Plant Sciences Institute. Researchers have uncovered a key to understanding the complex molecular mechanisms of hybrid vigor, also known as heterosis, which affects most aspects of plant growth and development. Once the gene activity behind hybrid vigor is well understood, scientists could more rapidly create hybrids that confer desired traits like ethanol production into the germplasm.

The research team, led by Patrick Schnable, professor of agronomy and director of the Center for Plant Genomics, includes Dan Nettleton, associate professor of statistics; and graduate students Ruth Swanson-Wagner, Yi Jia, Rhonda DeCook and Lisa Borsuk.

Their research is published in the May 2 issue of the scientific journal, Proceedings of the National Academy of Science ("All Possible Modes of Gene Action are Observed in a Global Comparison of Gene Expression in a Maize F1 Hybrid and Its Parents").

For the two-year experiment, the researchers used the maize F1 hybrid and its inbred parents corn lines, B73 and Mo17. The F1 is taller, matures more quickly and produces higher grain yields than both parents.

"We analyzed global patterns of gene expression in these three genotypes because this hybrid and its relatives are widely grown in the Corn Belt," Schnable said. "Also, the genetic map of corn is based on recombinant inbreds developed from this hybrid."

The researchers grew seedlings of the three genotypes in growth chambers to tightly control environmental effects. They isolated RNA from each of the three genotypes, and used a maize gene chip to determine the amount of RNA that accumulates for each gene in each of the three genotypes.

"We used this gene expression information to understand how each of thousands of genes behave in the genetic background, " Schnable said.

Using microarray technology, the researchers observed the activity of nearly 14,000 genes at the same time. The technology enabled them to look simultaneously at the gene expression of the hybrid and its inbred parents. This is the first study that has looked at hybrid vigor in any crop on such a large scale.

They found that some genes are more active in the hybrid than in both of the parental inbred lines (overdominant), some genes are less active than both inbred lines (underdominant) and most genes --78 percent -- have activity levels in between the level of the inbreds (additive).

"Several molecular models have been proposed to explain the phenomena of hybrid vigor. Some models require that genes exhibit overdominance or underdominance. Others assume that overdominant and underdominant gene expression is not an important contributor to hybrid vigor," Schnable said.

The results of the Iowa State experiment provide support for multiple mechanistic explanations for hybrid vigor.

"Although this research does not explain hybrid vigor, it begins to uncover what happens on a molecular level in a hybrid compared to the inbred parents. It shows us that there are multiple molecular mechanisms at work and that hybrid vigor is complex," Schnable said.

"To understand this important biological process, we will need to apply cutting-edge, high-throughput genomic technologies. The Plant Sciences Institute at Iowa State is one of very few public-sector organizations in the world that has the technology and resources necessary to conduct this research," he said.

The research findings provide a foundation for the Iowa State scientists to explore specific genes of interest, or investigate the contributions of the different mechanisms resulting in the gene expression patterns found. Their next step is to determine the genetic control of overdominance.

"Ultimately, it is likely that we would be able to predict which specific inbreds when crossed would produce a strong heterotic response. To a large extent, this is now a matter of trial and error. Consequently, we might be able to develop favorable hybrids more quickly for less cost. This would result in faster genetic gain," Schnable said.

Source: Iowa State University 2006


Read more at: https://phys.org/news/2006-05-mystery-hybrid-vigor.html#jCp
Click to expand...

Hey Gypsy Nirvana.

A+ Just excellent ! Thank you for that :)
 
C

cryptolab

New member
What makes this whole F1 Hybrid Vigour topic more puzzling...
is that the effect doesn't always show up.

So, perhaps the most famous example, of an F1 hybrid, is a mule.
Which is a hybrid between a horse and a donkey.
(Mules are normally sterile so you very rarely get second generation mules)

These animals are not more 'vigourous' than donkeys or horses.
These animals are not bigger than donkeys or horses.
However, they are longer lived, than horses and donkeys.

In contrast, ligers (a cross between a male lion and a female tiger)
are usually at least double the size of their parents.
Lions and tigers weigh 500 to 600 kilos (Tigers are generally slightly bigger)
Ligers get 'growth hormone' from genes in both parents and consequently they weigh
in at around 1000 kilos. The heaviest recorded liger was 1,600 kilos...
That's about 3 times the average weight of lions and tigers.

See the image below to get an idea of how massive ligers are:

zmulek4.jpg


Male and female ligers look most similar to (very large) female lions.
An odd detail about male ligers, is that, despite having a male lion as a father,
they don't have the shaggy lion's mane.

You might be forgiven for assuming that the genes for a male lion's shaggy
mane would come from 'dad'... but apparently, it comes from 'mum'.
Evidence for this can be seen in the picture of a male tigon shown below.
You can see that this animal obviously has a very pronounced lion's mane.
But tigons have a male tiger for a dad, and a lioness for a mum.
And since tigers don't have a 'mane'.. the tigon's mane must have come via mum.

A second interesting detail, is that tigons are either the same size as lions
or slightly smaller than lions (all depending on who's articles you read). But in
any event, tigons aren't bigger than either lions nor tigers.
Interestingly, the F1 hybrid vigour effect shows up for ligers but not for tigons.

jOXduoq.jpg


The third detail about these cats concerns tigon rarity. Ligers are quite
abundant, tigons are much rarer. The reason for this is that tigon cubs
are often still born. Tigons have a tiger dad and a lioness mum. Out of
the 4 cats (lion, lioness, tiger, tigress) tigers are the biggest
and lionesses are the smallest. An explanation for the tigon still births
is that cubs are physically too big to fit comfortably inside a lioness' womb.
This third detail, makes me wonder if the mixing of these genes is actually
haphazard and chaotic.

I wonder if, lions and tigers are simply not similar enough for the
'F1 Hybrid Vigour' effect to apply. Perhaps it would apply
much better, to the F1 hybrids of Bengal tigers and Siberian tigers.
Or perhaps to the F1 hybrids of African lions and Indian lions.
 
B

Betterhaff

Well-known member
Veteran
cryptolab, that link downloads as a pdf so maybe that's the issue why it doesn't work. I have it as a pdf file but the site doesn't let pdf's be attached. Search "Heterosis: Theory and Estimation". The authors are Kendall R. Lankey and Jode W. Edwards.

On the lion/tigon mane thing, in humans most male baldness comes from the maternal side’s contributions.

Also, lions and tigers are not the same species, they are in the same family and genus so other things at play there.





 
hyposomniac

hyposomniac

Well-known member
Veteran
Two selves locked in a single plant in a constant battle for dominance. Your mother's powerful family demands that you behave like a blueberry, meanwhile you look up to your father who is a ninja and a big wave surfer. You want to please them both. Such internal struggle can drive a plant to greatness and usually madness. Its metaphysical dudes.
 
Natural high

Natural high

Member
The explanation for hybrid vigour lies in the fact that recessive alleles tend to be the "weaker" or "less fit" alleles in an evolutionary sense, as opposed to dominant alleles.

All inbred lines have a high level of homozygousity. This means that many alleles which could be considered as sub-optimal will be expressed, as there is no overriding dominant allele.

When two inbred lines are brought together, the percentage of homozygous alleles is reduced as many are now paired up with a new different allele from the other parent. Of these new heterozygous pairings, the allele which is relatively "stronger" or "more fit" is more often than not the dominant one, hence the one which influences the final phenotype.




.
 
Last edited:
C

cryptolab

New member
Betterhaff said:
cryptolab, that link downloads as a pdf so maybe that's the issue why it doesn't work. I have it as a pdf file but the site doesn't let pdf's be attached. Search "Heterosis: Theory and Estimation". The authors are Kendall R. Lankey and Jode W. Edwards.

On the lion/tigon mane thing, in humans most male baldness comes from the maternal side’s contributions.

Also, lions and tigers are not the same species, they are in the same family and genus so other things at play there.
Click to expand...

Super! Thank you Betterhaff :)
 
MaryMaven

MaryMaven

Member
Natural high said:
The explanation for hybrid vigour lies in the fact that recessive alleles tend to be the "weaker" or "less fit" alleles in an evolutionary sense, as opposed to dominant alleles.

All inbred lines have a high level of homozygousity. This means that many alleles which could be considered as sub-optimal will be expressed, as there is no overriding dominant allele.

When two inbred lines are brought together, the percentage of homozygous alleles is reduced as many are now paired up with a new different allele from the other parent. Of these new heterozygous pairings, the allele which is relatively "stronger" or "more fit" is more often than not the dominant one, hence the one which influences the final phenotype.

.
Click to expand...


I'm sure there are more things at play than this in the grander scheme of things when it comes to hybrid vigor, but this quote from Natural high is quite eye/mind opening in its simplicity yet 'profoundness' :)


Thank you, all, for your contributions to this thread. Very, very interesting and a lot to think about!


I am just learning SOOOO much here at IC mag. It really is quite a unique site. I just love that so many here take their 'gardening' so seriously and their learning to the next level. The willingness of so many of you to share so much amazing, hard-earned knowledge with virtual strangers at no benefit to yourselves is 'philanthropy' at its very finest. I am so glad I found this site. :grouphug:


Peace
Maven
 
aridbud

aridbud

automeister
ICMag Donor
Veteran
Natural high said:
The explanation for hybrid vigour lies in the fact that recessive alleles tend to be the "weaker" or "less fit" alleles in an evolutionary sense, as opposed to dominant alleles.

All inbred lines have a high level of homozygousity. This means that many alleles which could be considered as sub-optimal will be expressed, as there is no overriding dominant allele.

When two inbred lines are brought together, the percentage of homozygous alleles is reduced as many are now paired up with a new different allele from the other parent. Of these new heterozygous pairings, the allele which is relatively "stronger" or "more fit" is more often than not the dominant one, hence the one which influences the final phenotype.




.
Click to expand...

Yup.
 
Farm Hero

Farm Hero

Member
Yes, hybrid vigor is real. In making UK Cheese X Black Widow, the first round was wild with variety and the vigor, now after S1F2 generation, the plants are quite stable and predictable. It's fun to witness hybrid vigor first hand, just be sure to use two very different yet stable genetic lines.


To me it is like both parents recognize they are very different and somehow put their most vigorous genetic expression forefront? Hybrid vigor plants have made great clone only varieties retaining the vigor over many years.
 
Natural high

Natural high

Member
Farm Hero said:
To me it is like both parents recognize they are very different and somehow put their most vigorous genetic expression forefront? Hybrid vigor plants have made great clone only varieties retaining the vigor over many years.
Click to expand...
It's not that they recognize that they are very different, but rather it happens inherently because of the dominance of some alleles over others as outlined in my post above. It is analogous to two card players combining average hands to make a better one.

UK cheese x black widow would make some awesome phenotypes i'd imagine. :)
 
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