Polyploidy: Definition, Types, Causes, and Examples

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What is Polyploidy?

As we all know chromosomes make up the important part of our cells by giving instructions for the production of certain enzymes and also in carrying the hereditary characters for future generation.

Any change or mutation in the structure or number of a chromosome results in chromosomal disorders.

Where any change in number of chromosomes is referred to as ploidy.

If there is addition of one or more numbers in a chromosome it is referred to as polyploidy.

Characteristics of Polyploidy

Polyploidy is a condition where the diploid cell consists of more than a 2n number of chromosomes than normal.

It results in many disorders and abnormalities in functioning of a cell. Where the cell with this polyploid condition has three or more extra chromosomes.

This condition often occurs in plants and other lower vertebrates like fishes and in amphibians. In plants it also especially occurs in angiosperms.

The most important type is allopolyploid which results in doubling or duplication of all chromosomes in a hybrid plant.

The polyploidy in plant is very beneficial as it induces the vigorous fertility in plants and gives good yield especially in angiosperms. so the farmers often feed the plant with some chemical polypoid triggers like colchicine.

Polyploid in animals is also not very common because it causes affects in most of the species.

Cause of Polyploidy

One of the major causes of ploidy is due to the non-disjunction of sister chromatids. This occurs mostly during the meiotic cell divisions.

Before undergoing meiosis, the chromosome number is doubled during gamete formation. These mutations in apical meristems results in doubling of growth in plants.

Polyploidy - research tweet 1

Allopolyploidy, which is a type of polyploidy results as a hybridization between two genome sets.

The combination of initial sterile hybrids with the other set of chromosomes results in sterile and genetically unstable condition of the plants; This on undergoing meiosis further doubles the chromosomes and creates a stable plant.

However, artificial polyploidy has been used in researches now a days for good commercial and economic purposes. Mostly the farmer uses the colchicine, the chemical inducer for the crops which interferes with the meiotic spindle formation.

Even the crosses are made between polyploids to increase the value of the vegetative parts of the plant. Usually banana, Bermuda is crossed between diploid and tetraploid species by the cultivars to increase the yield.

Types of Polyploidy

Generally, there are two types of ploidy they are autopolyploidy and allopolyploidy which is also known as amphipolyploidy. These are also subdivided into many categories.

1. Autopolyploidy

This condition results when there are multiple set of chromosomes and these chromosomes which form a multiple set are derived from a single genotype, which results in somatic doubling of cells and end up in formation of zygotes at the apical meristems.

Here the doubling occurs evenly and the existing chromosomes are doubled up, which results in multivalent pairing at the stage of meiosis.

There are two types of allopolyploidy as

a. Strict Autopolyploidy: This condition results in the doubling of chromosome evenly and it also occurs within the same individual.

b. Interracial Autopolyploidy: This condition occurs as a result of cross between different individual but these individuals have similar genotype.

2. Allopolyploidy

This condition occurs as a result of meiotic recombination’s between different genomes, so that the resultant obtained will be either odd or even in number.

This condition often results in bivalents of the species which increases the rate of fertility in offspring. Mostly allopolyploidy causes only reduced vigour in plants.

The economically important plants like strawberry, wheat, cotton, mustard, blueberry is grown with the help of allopolyploid inducing fertilizers which gives better yield.

Importance of Polyploidy

Polyploidy is one of the important and major cause the evolution the species. It is very important for the plants in increasing their vigour and size.

This phenomenon is similar to that of heterosis which helps in improving the economically important crops and flowering plants.

Polyploidy in Humans and Animals

As said earlier polyploid is a condition where an organism have a greater number of chromosomes than normal.

Most species of eukaryotes have their cell nuclei as a diploid condition which means that they have two set of chromosomes.

Each of them inherit their genes from each of the parents. As polyploid is most common in plants, it also occurs in humans and animals at some cases.

Polyploid generally occurs due to an abnormal cell division during the phases of mitosis or meiosis.

Polyploidy commonly occurs in highly differentiated tissues of our body such as in liver, heart muscles and in bone marrow and in the placenta regions. In animals such as lower vertebrates like fishes such as gold and salmon fish and also in amphibians such as salamanders.

It is rare occurring in human because it leads to death of the organism by duplicating the number of chromosomes.

Whereas in plants it results in diploid, triploid, tetraploid and hexaploidy which is often followed in food crops

Polyploidy vs Aneuploidy

Aneuploidy is a condition where the individual is having an extra number of chromosomes or loss or deletion one chromosome which leads to monosomy or deletion or addition of a chromosome to a normal pair results in trisomy.

These conditions give rise to various disorders such as Downs syndrome, Klinefelter’s syndrome and turners syndrome.

Where as Polyploidy is a condition where there will be addition of two or more set of the chromosomes and this condition mostly occurs only in plants and it is also beneficial among them by providing excess yield than normal and this condition is mostly possible with hybrid plants.

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