How will seedless fruits increase? Understand explanation of “polyploidy”!

Bananas used to contain a lot of hard seeds like red beans. Nowadays, bananas that have been seedless due to breeding are widely distributed. But why isn’t it extinct when there are no seeds and it shouldn’t be possible to grow? We will explain in an easy-to-understand manner the secrets of breeding, such as large grapes such as Kyoho, strawberries, and seedless watermelon.

Breeding makes it even more delicious! Fruits that are easy to eat and have changed

All the improved varieties of fruits are delicious and easy to eat. Approaching the wonder of breeding

Many fruits are originally sweet and delicious, but recently, many more easy-to-eat and delicious fruits such as large grapes, strawberries, and seedless watermelons have appeared. But while eating, do you ever have a simple question, “How did you make it?” “How can you increase it even though it is seedless?”

There are various ways to improve fruit varieties, but one of the keywords that explains how it works is “polyploid”. It’s a little technical word, but a typical example is “banana” that I usually eat.

Bananas that we often eat now are sweet and delicious, and even when we are busy, we can eat them just by peeling them, so it’s very easy. The lack of seeds is also one of the reasons for its popularity.

However, if you look closely at the cross section of the banana, you will see a pattern that looks like a remnant of the seed. Actually, as shown in the figure below (illustration), the original banana seeds were very difficult to eat because the flesh contained many hard seeds that were about the same size as azuki beans. So, while people in the old days pollinated and crossed various types of bananas, they happened to discover that they could produce sweeter and more nutritious bananas without seeds.

How will seedless fruits increase? Understand explanation of "polyploidy"!
The original banana seeds (left) contained a lot of large seeds and were difficult to eat, but a few thousand years ago, a seedless banana (right) was accidentally found. 
(Illustration drawn by the guide himself)

What is a polyploid?

A plant that has three or more sets of genetic information due to natural crossing and breeding.

Now, let’s be a little technical, but let’s explain what a polyploid is as easily as possible.

Among the cells that make up our body are spherical “nuclei” surrounded by membranes. Genetic information, which is a blueprint for making a body, is stored in it. In the case of human beings, one somatic cell has two sets of genetic information, including one set of genetic information given by the father and one set of genetic information dyed by the mother. In other words, human beings are “diploid” creatures. Almost all non-human animals are diploid, except in very special cases.

But in the case of plants, it is different. Due to natural crossing and artificial breeding, “triploids” with 3 sets of genetic information in one cell and “tetraploids” with 4 sets of genetic information can be found in familiar places. It exists.

However, since they are rarer than diploids, those with triploids of 3 or more are collectively called “haploids” to distinguish them.

One of the characteristics of “polyploid” is that it grows tall and bears big fruits.

DNA (deoxyribonucleic acid), which is the main body of genetic information, is engraved with a design drawing of the proteins that make up the body, so more proteins are made in polyploid cells. Since cells are made from it, the size of each cell increases. The larger the cells, the larger each organ, the organ, and the whole body.

There is “Kyoho” in the grape variety. It is troublesome to peel and eat small grapes one by one, but large grapes are easy to eat. And if it’s sweet and juicy, no one will hate it. In fact, Kyoho is tetraploid. By the way, old-fashioned grape varieties such as Delaware and Muscat of Alexandria are diploid. The tetraploid Kyoho fruit is larger than the diploid fruit.

However, “polyploidy” is not full of good things. Rather, it is “abnormal” in terms of the natural state of the plant, so inconveniences also occur.

Inconveniences and disadvantages that occur in polyploids

Even in humans, there are rare examples of triploids. However, since triploids cannot grow normally, they usually die in the mother’s stomach and cannot be born in this world.

The fact that polyploidy is more common in plants than in animals may be explained by the difference in the effects of chromosomal abnormalities on biological functions. Animals, especially humans, have a complex body structure, so even a slight abnormality can be fatal. On the other hand, relatively simple plants may be able to survive even if inconveniences occur. In the case of advanced machines, if something goes wrong, it will be completely unusable, but it is similar to the fact that old-fashioned simple machines can be used even if something goes wrong.

One of the inconveniences that occurs in triploid plants is “seedless”.

When the body’s cells divide into gametes (sperms or eggs in the case of animals) to leave offspring, the number of chromosomes is halved. This is called “meiosis”. A diploid with two sets of genetic information produces a gamete with one set of genetic information, which is used for reproduction. However, in the case of triploids, for example, the multiple of 3 is not divisible by 2, so meiosis cannot be done well and gametes cannot be made. Without a gamete, of course, fertilization would not be possible and seeds would not be possible.

In fact, the original species of banana was usually diploid and “seeded”. As mentioned above, while old people tried different types of banana mating, they happened to have triploid bananas. The triploids could not make gametes and became “seedless” even if they did. That is the “seedless” banana that we now like to eat.

Why are seedless bananas not extinct when they can’t produce more offspring?

I think the color and taste of bananas are different from those of today’s bananas, but “seedless” bananas were found thousands of years ago and have been eaten by us humans ever since.

Seedless bananas are seedless and cannot leave offspring. But why isn’t it extinct? Don’t you wonder?

There are two reasons. The first is that bananas are perennials. When a banana bears fruit, the above-ground part withers, but the underground part is alive and new shoots emerge from the rhizome. Since triploid buds come out from triploid strains, when the seasons come, they will bloom again and bear “seedless” fruits. If the environment does not change and this is repeated successfully, the same individual can continue to live.

However, in the natural world, the environment changes from moment to moment, so it is difficult for perennials to survive forever. There is another major reason why bananas are not extinct. This is because it was “very easy to eat and delicious” for us humans.

Bananas, whose “existence value” has been recognized by humans, have been cherished by humans and have been maintained for thousands of years so that individuals do not become extinct. Specifically, we humans have increased the number of plants by cutting off the seedless fruit-bearing banana buds and replanting them in different places. As a result, bananas can continue to bloom and bear “seedless” fruits every year, even if they have no offspring.

It is interesting that even though it is an “abnormal” individual that seems to be difficult to survive for a long time biologically, it is possible to live a long life by being “loved” by humans. Seedless bananas may teach us one way of survival strategy that “it is important for people to like us to live well“.

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