The heritable state of having more than two full sets of chromosomes is known as polyploidy. Did you know that polyploidy is usually thought to be a major evolutionary enabler? Let me explain, as we know polyploidy is a condition where the whole set of chromosomes is duplicated, this fixes heterozygosity, causing buffering of random mutation or factors modulating gene expression.

The buffering will allow new genes and gene functions to evolve while the original function remains in the other chromosome set. Even humans are believed to have evolved from polyploid ancestors. Read further to explore and learn about polyploids, their mechanism, and their advantages.

What is Polyploidy?

The heritable state of having more than two full sets of chromosomes is known as polyploidy. Polyploids are abundant in plants, as well as some fish and amphibian species. Examples of polyploids include salamanders, frogs, and leeches. Many of these polyploid creatures are well-suited to their surroundings. Indeed, new genomic research indicates that many presently diploid animals, including humans, descended from polyploid predecessors.

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Mechanism of Polyploidy

Polyploidy occurs when cells divide abnormally, either during mitosis or, more typically, during metaphase I of meiosis (it may arise from the failure of chromosomes to separate during meiosis or from the fertilization of an egg by more than one sperm). In addition, several substances can cause it in plants and cell cultures: the most well-known is colchicine, which can cause chromosomal doubling, but its usage may have other, less evident side effects. Oryzalin will also double the content of existing chromosomes. Oryzalin is a herbicide that may be used instead of colchicine to induce polyploidy in plants.

Fig: Mechanism of formation of Autotetraploid

Types of Polyploidy

The three kinds of polyploidy are allopolyploidy, autopolyploidy, and auto-allopolyploidy.

1. Allopolyploidy: a polyploid individual or strain with a chromosomal set made up of two or more chromosome sets originating from other species that are more or less complete. Examples: the allohexaploid Triticum aestivum, allotetraploid Gossypium, and mules.
2. Autopolyploidy: an individual or strain with more than two full copies of a single ancestral species’ genome on its chromosomal complement. Example: piggyback plant, Tolmiea menzisii and the white sturgeon, Acipenser transmontanum.
3. Auto-allopolyploidy: It is a special case of polyploidy where an allopolyploid individual also shows the characteristics of auto-polyploidy for one or more genomes.

Other types of polyploidies are:

1. Triploid (three sets of chromosomes; 3x), example seedless watermelons
2. Tetraploid (four sets of chromosomes; 4x), example Salmonidae fish
3. Pentaploid (five sets of chromosomes; 5x), example Kenai Birch (Betula kenaica)
4. Hexaploid (six sets of chromosomes; 6x), example wheat, kiwifruit

Fig: Types of Polyploid

Aneuploidy Vs. Polyploidy

Below we have provided the difference between Aneuploidy and Polyploidy:

Polyploidy	Aneuploidy
Presence of more than two sets of homologous chromosomes	Presence of an abnormal number of chromosomes due to presence or absence of 1 or 2 chromosomes.
It is rare in human	It is common in human
Different types of polyploids are triploid, tetraploid, etc	Different types of aneuploidies are nullisomy, monosomy, etc
Triploid and tetraploid conditions are lethal	Cause various diseases with no cure

Advantages of Polyploidy

Polyploidy presents itself with various advantages which are listed below:

1. The polyploid offspring of two diploid progenitors are more vigorous and healthier than either of the two diploid parents, a phenomenon known as hybrid vigour or heterosis.
2. Gene redundancy: Because the polyploid kids now have twice as many copies of each gene, they are no longer susceptible to the harmful consequences of recessive mutations.
3. When tiny, isolated populations are forced to inbreed, the protective impact of polyploidy may be crucial.
4. Polyploidy provides the ability to change the function of genes throughout time In other words, excess copies of genes that aren’t needed for regular organism function might wind up being employed in new and unexpected ways, resulting in new evolutionary selection chances.
5. Polyploidy has the potential to influence sexuality in ways that offer selection benefits.
6. Polyploidy also provides an evolutionary advantage. It is believed that humans descended from polyploid ancestors.

Disadvantages of Polyploidy

Despite having many advantages, polyploidy also poses various disadvantages which are listed below:

1. The variations in the size of the genome in relation to the volume of the cell
2. Polyploidy can also make it difficult for mitosis and meiosis to complete normally, resulting in aberrant segregation patterns such as 3:1 or 2:1 plus one laggards.
3. Changes in gene expression are a possibility.
4. Polyploidization, which causes epigenetic instability, can result in extensive alterations in epigenetic regulation.

Applications of Polyploidy

Polyploidy is effectively used in plant breeding to produce improved variety. Polyploidy is utilised to change the colour of the flour, as well as its size and form. Crop diversity may be achieved with the use of polyploidy. Polyploidy is important for crop analysis and development. Many crops have been discovered that have been domesticated due to polyploidy. Wheat is often regarded as the world’s most important food. This is a kind of grass that is frequently planted for the production of cereal meals. Wheat is one of the best instances of polyploidy because it develops naturally. Antimitotic chemicals, which aid plant reproduction, are sometimes used to artificially produce polyploidy. Polyploidy occurs when the complete set of chromosomes is duplicated, resulting in a new variety. One of the most important effects of polyploidy is that it aids in cell growth owing to the additional gene copies.

Summary

The heritable state of having more than two full sets of chromosomes is known as polyploidy. Polyploids are abundant in plants, as well as some fish and amphibian species. Polyploids include salamanders, frogs, and leeches, for example. Many of these polyploid creatures are well-suited to their surroundings. Polyploidy occurs when cells divide abnormally, either during mitosis or, more typically, during metaphase I of meiosis. The three kinds of polyploidy are allopolyploidy, autopolyploidy, and auto-allopolyploidy. Other types of polyploidies are Triploid (three sets; 3x), Tetraploid (four sets; 4x), Pentaploid (five sets; 5x), Hexaploid, etc.

Polyploidy is different from aneuploidy as polyploidy refers to the presence of more than two sets of homologous chromosomes whereas aneuploidy refers to the presence of an abnormal number of chromosomes due to the presence or absence of 1 or 2 chromosomes. Polyploidy presents itself with various advantages like hybrid vigour or heterosis and Gene redundancy etc. Despite having many advantages, polyploidy also poses various disadvantages like variations in the size of the genome in relation to the volume of the cell, Changes in gene expression, etc. Polyploidy is effectively used in plant breeding to produce improved variety. Polyploidy is used to change the colour of the flour, as well as its size and form. Crop diversity may be achieved with the use of polyploidy.

Frequently Asked Questions (FAQs) related to Polyploidy

Q.1. Are humans polyploid?
Ans: Although polyploid cells can be seen in highly differentiated tissue such as the liver parenchyma, heart muscle, placenta, and bone marrow, true polyploidy is uncommon in humans.

Q.2. Is polyploidy lethal in humans?
Ans: Some polyploids such as triploid XXX humans are lethal in humans.

Q.3. Who discovered polyploidy?
Ans: Polyploidy was discovered by Ledyard Stebbins

Q.4. Give an example of a natural polyploid?
Ans: Piggyback plant (Tolmiea menzisii) and the white sturgeon, (Acipenser transmontanum) are examples of natural polyploidy.

Q.5. What are synthetic polyploids?
Ans: A synthetic polyploid is a plant that has been regenerated from oryzalin-treated callus and has a doubled genome relative to its parent.

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