Hybrids

I just had a random question in my head and figured a permie could answer it. How are hybrids predictable? I mean, when the cross two varieties, I would think a lot of progeny would be produced that are all somewhat unique- like siblings are not all identical. But with an F1 hybrid, it seems you get predictable results. Are my assumptions wrong? How does this work?

The parents of commercial hybrids are hyper-inbred. No diversity is possible in the F1 offspring, because the parent varieties lack diversity.

Joseph Lofthouse wrote:The parents of commercial hybrids are hyper-inbred. No diversity is possible in the F1 offspring, because the parent varieties lack diversity.

I have much to learn about genetics. I don’t think I understand it still. My brothers and I have identical parents but we are not identical to each other. Is it that the plant parents have the exact same copies of each gene? Is that what you mean by lacking genetic diversity?

Thank you for taking time to answer my question.

Let's picture that for each of your parents, their parents were siblings. And their grandparents were siblings... Going back generations. And only children that 'looked the Same' continued the next generation.

We have two copies of our chromosomes, essentially (neglecting some detail), one from each parent.  One from each parent. Two copies of each gene.

If you interbreed a thing for long enough, you end up with both copies of genes, from both parents, being the same for traits we care about, like colour, days to maturity, size, sweetness, etc.  So it doesn't matter really, always, you will have the same progeny (ignoring a mutation, or a few other things), so long as you keep breeding that line.

If you take two inbred things from different "varieties" we can predict pretty exactly what the progeny will have for genes. It's repeatable.

Say the father has genes

AA
BB
CC

and the mother has

aa
bb
cc

All the offspring will be

Aa
Bb
Cc

Those genes behave predictably - so we know that all offspring of very inbred parents, will essentially have the same genes.

But if we start crossing the hybrid offspring, things get way less predictable! Because the parents have a mix of genes, and we can't predict which offspring will get which. And we start getting super cool things happening, from traits that may have more than one gene controlling them.

You can get more technical and start talking about recessive, dominant, and codominant traits. But that's the basics.

Since your parents aren't inbred for multiple generations, you and your siblings should definitely not look identical :)

Catie George wrote:Let's picture that for each of your parents, their parents were siblings. And their grandparents were siblings... Going back generations. And only children that 'looked the Same' continued the next generation.

We have two copies of our chromosomes, essentially (neglecting some detail), one from each parent.  One from each parent. Two copies of each gene.

If you interbreed a thing for long enough, you end up with both copies of genes, from both parents, being the same for traits we care about, like colour, days to maturity, size, sweetness, etc.  So it doesn't matter really, always, you will have the same progeny (ignoring a mutation, or a few other things), so long as you keep breeding that line.

If you take two inbred things from different "varieties" we can predict pretty exactly what the progeny will have for genes. It's repeatable.

Say the father has genes

AA
BB
CC

and the mother has

aa
bb
cc

All the offspring will be

Aa
Bb
Cc

Those genes behave predictably - so we know that all offspring of very inbred parents, will essentially have the same genes.

But if we start crossing the hybrid offspring, things get way less predictable! Because the parents have a mix of genes, and we can't predict which offspring will get which. And we start getting super cool things happening, from traits that may have more than one gene controlling them.

You can get more technical and start talking about recessive, dominant, and codominant traits. But that's the basics.

Since your parents aren't inbred for multiple generations, you and your siblings should definitely not look identical :)

Thano you, that makes total sense to me now.

Tomatoes contain around 32,000 genes. In the highly inbred tomatoes essentially all 32,000 pairs of corresponding alleles are identical.

Inbreds fail to thrive. With tomatoes, the hybrids average 50% more productivity than the highly inbred heirlooms from which they descend.

Joseph Lofthouse wrote:Tomatoes contain around 32,000 genes. In the highly inbred tomatoes essentially all 32,000 pairs of corresponding alleles are identical.

Inbreds fail to thrive. With tomatoes, the hybrids average 50% more productivity than the highly inbred heirlooms from which they descend.

Wow, amazing info and very enlightening. It’s possible that’s in your book and I forgot. If so, thanks for helping me remember.

Additional fun fact:  Using the same tools for estimating the gene number in tomato at 32,000 - 35,000, the Human Genome Consortium pegs the human genome to contain ~20,000 genes.  

I always lose the argument when I'm disagreeing with a point my Roma tomatoes are trying to make! :-)  .... clearly they have he edge on intelligence with some of those extra genes....lol

... I need to pick on that weed over there in the corner instead....Arabidopsis thaliana aka "Mouse-eared cress".  We have the same gene number, but I'm the one with the garden hoe!....

Ha!