When I was younger, some of my friends believed that if they ate watermelon seeds, a watermelon would grow in their stomachs. They didn’t realize that their stomachs are too dark and for watermelons to grow, they would need light. Additionally, our stomachs are acidic and hence aren’t a good place for watermelons to grow. Regardless of the fact that watermelon seeds and other seeds can’t grow in tummies, some people still prefer seedless fruits.
According to Wikipedia, fruits are defined as, “In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering.” This means that fruits literally must have seeds, or they technically are not considered ‘fruits.’ Seedless fruits technically can’t reproduce because they don’t have any seeds to reproduce from. So, then how do seedless fruits appear in the environment?
Fruits are living things and hence are made up of DNA. DNA (deoxyribonucleic acid) is like a blueprint for how to “build” a living organism. It decides whether someone is going to have blue eyes or brown eyes. Or, in the case of fruits, for example, what color the seeds are going to be. But, sometimes, during DNA replication (when DNA is copying itself to produce more cells), there is a mutation, or a change in the DNA structure, that can change the organism somehow. For example, the occurrence of blue eyes in humans was a mutation. In the case of fruits, some fruits become parthenocarpic. Parthenocarpy stems from the Greek words ‘parthnos’ which means virgin and ‘karpos’ which means fruit. Hence, parthenocarpy means a fruit grown without fertilization.
Usually, this is a result of a genetic mutation.
Another reason a fruit might be parthenocarpic is if the ovary/sperm is nonfunctional or if pollination fails. Citrus farmers who grow seedless fruits exploit this feature and plant clones of seedless fruits. These trees don’t require seeds and are still able to grow seedless fruits.
And yet, another reason is chromosomal imbalance among these fruits. We humans have 23 sets of two chromosomes (in total 46 chromosomes). Each species has its own number of chromosomes but the animals within the species are supposed to have the same number of chromosomes. If humans have an extra chromosome or not enough, it leads to serious effects. This is because chromosomes contain two long strands of DNA. DNA is made up of a phosphate group, a sugar group, and four nitrogenous bases — adenine, thymine, guanine, and cytosine. Adenine pairs up with thymine and cytosine pairs up with guanine. If there is a genetic mutation, the change occurs in a base pair in DNA. But, if there is a chromosomal mutation, millions of base pairs are affected. And, if there is an additional chromosome, that’s countless genes that aren’t needed. Some conditions in humans that are the result of not enough chromosomes or too many chromosomes is Down Syndrome (an extra copy of chromosome 21), Turner’s Syndrome (females having only one X chromosome instead of the usual two X chromosomes), and Klinefelter Syndrome (males having more than one X chromosome and one Y chromosome instead of the usual one X chromosome and one Y chromosome). Humans are diploid which means we have two sets of chromosomes. Bananas, on the other hand, are triploids which means they have three sets of chromosomes. This chromosomal imbalance has led them to be sterile and hence not able to produce proper seeds.
The bananas that we eat today are all sterile and seedless. Bananas and seedless grapes “reproduce” through cloning. Cuttings are taken from a mother plant that produces seedless fruits (in seedless grapes, stems are sliced diagonally and cut into sections). The cuttings are then dipped into a rooting hormone. Then, they are planted. The new offspring produce seedless fruits and are also clones because their DNA completely matches the mother plant’s..
Watermelons use colchicine which is a chemical that occurs naturally in the environment. It is toxic in large doses (but in small doses, it is used to treat gout, a form of arthritis). Colchicine messes with cell division. When colchicine is used on watermelon seeds or on their parent plants, the flowers from which watermelons come from have twice as many chromosomes as they should. When pollen from a plant that hasn’t been affected by colchicine is used to pollinate the flower, the offspring has three sets of chromosomes and hence becomes triploid. And then, the offspring’s flowers produce seedless watermelons.
Some people find seedless varieties of fruits easier to eat and sometimes tastier. Another reason why seedless fruits are sold is that they have a better shelf life. On the other hand, seeds are a source of fiber which we won’t get if we only eat seedless fruits. But, if a person really doesn’t like seeds (they are a little bit bitter, after all), they can get their fiber from a different food source.
As one can see, there are a lot of ways in which fruits become seedless. This only adds to the complexity and diversity of species around us.
Vaageesha Das is a sophomore at Morgantown High School. Today’s information comes from: Burr, B. and Burr, F., 2000. How Do Seedless Fruits Arise And How Are They Propagated? [online] Scientific American. Available at: <https://www.scientificamerican.com/article/how-do-seedless-fruits-ar/; Wikipedia. 2020. Fruit. [online] Available at: <https://en.wikipedia.org/wiki/Fruit#:; text=In%20botany%2C%20a%20fruit%20is,by%20which%20angiosperms%20disseminate%20seeds.; Pathwayz.org. 2020. GENETICS / CHROMOSOMAL MUTATIONS – Pathwayz. [online] Available at: <https://www.pathwayz.org/Tree/Plain/CHROMOSOMAL+MUTATIONS;Wonderopolis.org. 2020. How Are Seedless Fruits Made? [online] Available at: <https://www.wonderopolis.org/wonder/how-are-seedless-fruits-made; Scienceline.ucsb.edu. 2012. I Was Just Wondering How Many Chromosomes It Takes To Make One Strand Of DNA? Thanks, Hopefully You Reply Soon.. [online] Available at: <http://scienceline.ucsb.edu/getkey.php?key=2872#::text=One%20chromosome%20has%202%20strands,4%20DNA%20bases%20in%20strings; SciShow, 2013. The Terrifying Truth About Bananas. Available at: <https://www.youtube.com/watch?v=ex0URF-hWj4; Seeker, 2015. How Do Farmers Make Seedless Fruit? Available at: <https://www.youtube.com/watch?v=ewtlsEb4Vgk; Stöppler, M., 2019. 21 Common Genetic Disorders: Types, Symptoms, Causes & Human Genome. [online] RxList. Available at: <https://www.rxlist.com/genetic_disease/article.htm; TRUE FOOD TV, 2015. APPLE | How Does It Grow? Available at: <https://www.youtube.com/watch?v=UWLmEh1HIBw; TRUE FOOD TV, 2019. Seedless Fruits: Are They Gmos? Available at: <https://www.youtube.com/watch?v=FbHTTEdC2-o; TRUEFOODTV, 2017. SEEDLESS Watermelon — You’ll Never Guess How It’s Grown. Available at: <https://www.youtube.com/watch?v=ohN0y03yMco; Do seedless fruits have negative side effects? (n.d.). LIVESTRONG.COM. Retrieved, from https://www.livestrong.com/article/402800-do-seedless-fruits-have-negative-side-effects/
