When an organism’s cells have more than one set of (homologous) chromosomes, it is referred to as polyploidy. When chromosomes fail to split during meiosis or when more than one sperm fertilises an egg, polyploidy can result. Here, let’s discuss the different types of polyploids.
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What Is Polyploidy?
A polyploid organism is one that has more than two genomes. There are species in numerous plant genera whose chromosome counts form a euploid sequence. For instance, species in the genus Rosa (roses) have somatic numbers 14, 21, 28, 35, 42, and 56. These figures are multiples of seven. As a result, the basic monoploid number 7 produces species that are diploid, triploid, tetraploid, pentaploid, hexaploid and octaploid. All of these other than the diploids are called polyploids.
Natural populations rarely experience ploidy levels higher than tetraploids. However, the most important crops and ornamental plants are polyploids, such as wheat (Hexaploid 6x) and strawberries (octaploid, 8x). In general, polyploidy is uncommon in animals but prevalent in plants (particularly so in monocots).
In actuality, more than 30% of plants are polyploid. In comparison to diploid plants, the size of various organs like leaves and cells is often bigger in polyploid plants. Furthermore, it appears that polyploid plants are more resistant to adverse environmental circumstances.
Types of Polyploidy
The following are the three major kinds of polyploids :
- Allopolyploids
- Autopolyploids
- Autoallopolyploids.
Allopolyploids
When an F1 hybrid that is created from two clearly distinct species develops polyploidy as a result of doubling the number of chromosomes, this phenomenon is known as allopolyploidy. The resultant species is referred to as an allopolyploid.
Unreduced (2n) gametes are fused in order to do this, which can happen either before or after hybridization. Reduced gametes from two autotetraploid taxa or unreduced gametes from each diploid taxon unite to create allopolyploid offspring in the former scenario. In the latter scenario, a single or more than one diploid F1 hybrids create unreduced gametes that combine to produce allopolyploid offspring.
Also Check: Important Notes for NEET Biology – Principles of Inheritance and Variation
Autopolyploids
Autopolyploids are those that have the same basic set of chromosomes multiplied. For instance, an autotriploid species will have three similar genomes (AAA) and an autotetraploid species will have four similar genomes (AAAA). Many plant and animal cells have had autopolyploidy induced by artificial techniques such as chemicals, temperature shocks and radioactive materials. During cell divisions, these inducers typically disrupt the mitotic or meiotic spindle and prevent the segregation of chromosomes that have already been replicated. This can also result in the gigantism of plant cells.
Autoallopolyploids
This phrase refers to a unique circumstance in which an allopolyploid individual additionally demonstrates the traits of autopolyploidy for one or more than one genomes.
Polyploidy in Animals
Animals rarely exhibit polyploidy, but leeches, flatworms and brine shrimp do. Additionally, in mice, 40% of liver cells are tetraploid and 5% are octoploid. Human liver cells and cancer cells have been revealed to contain polyploid DNA. Whether full or as a mosaic, polyploidy in them causes severe deformities and mortality.
This was a brief note on polyploidy. For more NEET related content, visit BYJU’S.
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