I’m still not buying this. If it – the apple, not its seeds – was a “genetic jumble” rather than a Red Delicious apple, it wouldn’t grow into a Red Delicious Apple. The genetric code is where it gets instructions to grow into a Reed Delicious Apple. Just as your own DNA (not of the eggs inside you) must be the genetic code of Why Not, or else, if you get an injury, it might grow into Brundlefly.
Clarifying question: if I could somehow completely isolate two Red Delicious trees, and allow them to pollinate each other, would I get Red Delicious seeds from the resulting fruit? If not, where is the jumbled DNA coming from? Is there some inherent scrambling that occurs when a tree passes down its genes? Bear in mind I skipped biology to take more physics in high school…
I asked this back in #3, and the answer is clearly No. You can go back and read the responses.
That’s what I thought the first time I read WhyNot’s response - but rereading it, I think it’s different. The apple is completely unaffected by pollination, because it’s part of the tree, but I don’t think (I could be totally wrong here) that WhyNot was talking about the seeds, there.
Yes, that’s right. The cells in the apple fruit are from the parent tree. The cells in the apple seeds are the offspring of the parent tree, and whatever parent tree provided the pollen.
The genetic code of the egg/ovule is entirely derived from the mother, and the genetic code of the pollen (or sperm). Except the gametes aren’t exact copies of the parent, because each gamete is haploid (one copy of each chromosome) rather than diploid (two copies of each chromosome). Note that plants are sometimes polyploid and might contain four or six copies of each chromosome rather than two. So the egg that made you contained half the genetic information of your mother, the sperm that made you contained half the genetic information of your father, and they combined to make a you. And your sperm are haploid, and will contain a random mix of chromosomes–some from your mother, some from your father, but only half of your total. And chromosomes themselves can split apart and fuse back together, this process is called crossing over.
Most organisms have multiple copies of their genome. Humans are diploid, we’ve got two copies of each gene. Plants, are triploid or polyploid, so they’ve got multiple copies of each gene. Each copy can be different, if this is the case the organism is said to be heterozygous for that particular gene. Apples in particular have extremely high heterozygosity – lots of their genes are present in multiple forms.
Now, the Red Delicious variety does have a particular genotype that consistently produces a “red delicious” phenotype. But it has lots of recessive genes that would express a different trait if given a chance. When the apple produces offspring, even by self-fertilization, all of those genetic variants are randomly reassorted.
For example, there could be a particular gene that determines the color of an apple. One variant, let’s call it R is a dominant gene (or allele to be more precise) that always results in a Red apple. Other variants, Y and G, produce yellow or green apples, but only in the absence of the R variant. So the Red Delicious might have a genotype with one of each variant – RYG. Its offspring could have any possible combination of those genes – RRR giving a red color, YYY giving yellow, and YGG giving… something I haven’t specified in this hypothetical.
That’s vastly oversimplified, of course, but there are thousands of genes (and by extension traits) with that sort of potential for variation. The net result is that any offspring will probably be a radically different sort of apple from its parent.
Cloning, grafting, etc, are asexual - genes are transferred from the “parent” to the “offspring” with no change whatsoever.
Going through seeds is a sexual process, which involves a huge amount of reshuffling. Half of the parent’s chromosomes are selected at random, and combined with half of another parent’s genes, which are also selected at random. For simplicity’s sake, we can say that both parents are the same tree - self-pollination. The offspring is still not going to be identical to the parent.
Here’s an example: Let’s take a gene - gene A. The parent tree has two copies of this gene, and let’s say they come in two flavors, A and a. This gene could code for apple size, or branch length, or whatever. It doesn’t really matter. So half of the gametes produced will have an A in them and the other half will have an a. Let’s fertilize. You now can get AA, Aa, or aa, in a 1:2:1 ratio. In other words, only half of the offspring are identical to the parent at this gene.
Multiply this process by the tens of thousands of genes in your organism, and even accounting for the proportion that are parentally homozygous, you can see that the odds of having an offspring that’s genetically identical to the parent are vanishingly small.
So, why does this mean that you’d get bad apples from an offspring plant? That I don’t know. I’m not a botanist. It would appear that only a very specific combination of genetic alleles give rise to fruit that has the desired characteristic. I suppose we could set out to map them all and figure out exactly which genes are important to what, and then breed strains of trees that pass these characteristics on with complete fidelity, but it’s much easier and cheaper to just grow cuttings.
The answer is no, you can’t cross two Red Delicious apples. This is because apple trees are incapable of self-fertillization. Or another way to think of it, is that an apple won’t allow itself to be fertilized by itself, it won’t allow pollen from itself to form a pollen tube. Imagine if humans were hermaphrodites, and you masturbated and your sperm fertillized your own egg. That’s pretty severe inbreeding, and so many/most hermaphroditic species (like most plants) have physiological mechanisms to prevent this from happening.
But some plants do allow selfing, in fact sweet peas have closed flowers and are therefore obligate selfers. However, selfing is not the same as cloning, because the sperm and eggs are haploid. So suppose you had 4 chromosomes. In a diploid adult, that would mean one copy of each chromosome from your parents. So you’d have FMFMFMFM–one copy from your female parent, one from your male parent. But your sperm and eggs would have a random assortment of those chromosomes. You’d have one copy of each, but it would be random whether that copy came from your mother or your father.
So a gamete might have FFFF, FFFM, FFMF, MMFF, MMMF, and so on any permutation of chromosomes (and in fact, even finer than this because chromosomes cross over as mentioned above). And so if a FFFF gamete fertillized a MMMM gamete, the resulting FMFMFMFM offspring would be genetically identical to you. But what if a FFMM gamete fertillized a FFMM gamete? The result would be a FFFFMMMM offspring, which would be similar to you but not identical. So you can see that in selfing the resulting offspring could be very similar to the parent, but not identical. But given multiple generations of selfing, eventually you’d lose genetic information and you’d be homozygous at all alleles. This is what happens in regular old inbreeding, but faster.
I know very little about this matter. However, reading this thread, I wonder if it might be easier to explain the issue if one were to say “A specific type of apple, such as red delicious, is not a true ‘cultivar’? The characteristics of the fruit of any particular cultivar of apple tree have sufficient variability that they do not reliably produce apples that are good to eat, much less more specific characteristics that define a category such as ‘red delicious’?”
Would that be correct?
Note that the term I see used for describing the mutation that produces a new variety of fruit is a (bud) sport. So a long time ago someone noticed a nifty tasting apple on one branch of a tree that was better than the others. So a graft was made from that branch, etc.
The very endmost growing tip of a tree branch is susceptible to mutation and then reproducing that mutation as the branch grows from that point.
People don’t really look for new apple varieties via cross breeding. They look for unusual apples on one branch of a tree.
A couple of clarifications wich might help:
Crossing two red delicious trees does not equal crossing two humans, or even two EnterRaceHere, or even two Meachams; it equals crossing two CalMeachams. Even still, as you are crossing the two CalMeachams, there’s a good chance that dominant traits will win out, so the result will not equal a CalMeacham. If the traits you are hoping to get are non-dominant, you still won’t get them.
Also, the apple does not equal the baby; it equals the placenta. the seed equals the baby.
Quoth TrueCelt:
Actually, the non-dominant ones are the ones that are guaranteed, at least if you’re doing self-crossings. If you’ve got recessive genes being expressed, then you know that you don’t have any dominants hiding behind them, just waiting for their opportunity to show up. With dominants, though, you can never be sure what the other copy (or copies, for polyploid organisms) is.
Quoth lazybratsche:
Actually, I’m pretty sure that most plants are diploid, too. While polyploidy is certainly much more common in plants than in animals, the odd numbers will lead to sexual infertility. This is why, for instance, bananas don’t have (noticeable) seeds: They’re triploid. Diploid or tetraploid bananas do exist, but they have big awkward seeds that make them not as good for eating.
I think you can probably still describe that in terms of Mendelian genetics, it’s just that instead of dealing with a single trait ‘tall’ vs ‘short’ (or ‘red’ vs ‘white’), you’re dealing with dozens of possibly-overlapping, subtle traits that conspire, in one particular permutation, to produce the red delicious apple.
If we compare Mendel’s tall vs short to the heads vs tails result of tossing of a coin, maybe Red Delicious is comparable to winning the lottery, vs lots of different ways to lose.
“Most” plants may be diploid, but most angiosperms aren’t. Nor are most of the plants we consume as modern humans.
Angiosperms have high levels of polyploidy in general (there’s some evidence that chromosome levels kind of fluctuate along any given species’ evolutionary development) and, in particular, human selection has introduced it into a lot of our modern plants. Obviously, more chromosomes does not always equal more proteins which does not always equal high fitness - but sometimes it does. Unintentionally (like the domestication you’ll read about in Guns, Germs, and Steel) or deliberately (as in the hexaploid kiwi or the chemically mutated 3n seedless watermelon) increasing the ploidy level can lead to lots of desirable traits.
As to the OP’s question - it’s already been answered and is of course because many reproductive steps exist to introduce genetic variation between generations and, if you’ve got the perfect delicious sugary genome (or not), you don’t want to leave it to chance. DNA chains will be all promiscuously entangling each other and microtubules will be ripping the wrong copies of the genes into each respective gamete and really…it’s all much too messy for industrialized agriculture.
Zombie clone apple rule.
So figuratively speaking, the apple CAN fall far from the tree.
Yes, there are people still breeding & researching to find better apples. The University of Minnesota Agricultural Research station has been doing so since 1908.
They developed the apple now known as HoneyCrisp somewhere in the early 1970’s, and released it in 1991. It was believed to be a hybrid of Macoun & Honeygold, but DNA testing has now shown that it comes from neither of them. The actual parentage remains unknown.
They developed the Zestar apple in the early 1990’s, and released it in 1996. It had good taste & juicyness, but seems to work best as a cooking apple.
Their latest is the SweeTango, which is a hybrid of the female Honeycrisp crossed with male Zestar, first made in 1988. Trees have been sold to apple growers, and the apples just started showing up in a few grocery stores last year. They are expected to be more widely available this year & next.
So research into apple varieties continues.
I was told once that I could plant the stone of a variety of peach that we had in this area (Switzerland) and get a tree of the same variety without having to graft it. I suppose its genes were stabilized ?
A quick internet search reveals that peaches can indeed be grown from seeds. It’s cautioned that you might not get a great fruit, but the warning is far less severe than with fruits like apples, pears, etc. So evidently genes for “good” peaches aren’t as rare. The tree matures faster than apples, too, yielding fruit in less time.
Not all fruits require grafting to produce acceptable fruit. You can get perfectly acceptable grapes and berries from seeds, for instance.
I think it’s more likely that the person who told you that was mistaken. Peach trees, like other stone fruits, have to be grown from graft to produce true, just like apples. How to Plant a Peach Seed: Growing a Fruit Tree in Your Backyard