Polyploidy

The polyploidy is a condition in which a cell or organism normally diploid acquires one or more additional sets of chromosomes . In other words, the polyploid cell or organism has three or more times the number of haploid chromosomes. Polyploidy arises as a result of the total nondisjunction of chromosomes during mitosis or meiosis . Polyploidy is a very common process among plants and has, in fact, been an important source of speciation in angiosperms .

What is polyploidy?

The word polyploidy means having multiple sets or complete groups of genetic information . When we refer to genetic information, we refer to everything that is needed to be able to give rise to a living organism and generally these organisms have more than two sets of information.

Most of the creatures that reproduce sexually have an even number of information groups, which, as we already know, come from the mother and the father , it is also important to remember that these information groups are similar , but they are not identical .

That said, we can say that polyploidy is an increase that occurs in the number of chromosomes that are normally found within the diploid complement . Polyploidy is generated due to some irregularities that occur during the meiosis process : in the first division or prophase, when homologous chromosomes pair up to form tetrads , and do not separate during anaphase I ; a situation that causes one cell to have all the chromosomal complement and the other to have none.

Types

Scientists have come up with many terms to describe ploidy, or the number of sets of genetic information required to create a living thing. There are two major divisions that in turn have subdivisions , these are the following:

Euploidy

It occurs when there is a numerical alteration in the total number of chromosomes and is classified into the following subdivisions:

• Monoploid : it has a single basic set of chromosomes of the species, it is expressed as no x. We can see it in fungi, in bees and male wasps; in plants it produces sterile organisms.
• Triploid – They have three complete sets of chromosomes . They are quite strange to see because although they can survive, as in plants, they are usually sterile as they have defective gametes .
• Tetraploids : They have four sets of chromosomes . The duplication is carried out by means of chemical compounds , and it originates when two diploid gametes of the same species unite .
• Autotetraploids : they have four sets of complete homologous chromosomes . They are fertile when they have balanced gametes , and are formed when two non-reduced gametes of individuals belonging to the same species unite.
• Allotetraploids : they are formed by four sets of non-homologous chromosomes . They are fertile and are formed when two diploid gametes of two different species come together.

Aneuploidy

These are organisms that do not have multiple chromosomes in their basic number. They have the following subdivision.

• Nulosomic : occurs when an organism loses a pair of chromosomes . It is a deadly situation for diploids.
• Monosomic : it happens when diploids lose a chromosome in one of their pairs and the mortality rate is very high, in addition to presenting a reduction in fertility.
• Trisomic : shown in diploids that have an extra chromosome . This gives rise to different phenotypes ; in humans the presence of a small extra chromosome produces Down syndrome.
• Double Trisomic : occurs when each of two different chromosomes is tripled .
• Tetrasomic : it is given by the multiplication of a chromosome in a diploid organism.

Polyploidy in animals

Polyploidy is more common in plants than in animals, although the exact reason is unknown with certainty, although experts believe that it may be due to the type of development and the form of sexual reproduction of animals. Some scientists think that it is due to the degree of complexity that the bodies of animals present compared to that of plants. However, there are some exceptions as in the case of fish , reptiles and some insects .

Polyploidy in plants

We can locate it in all plant groups and it has played an important role in their evolution. This process allows the silvers to make genetic changes that in turn produce phenotypic or environmental changes . It is a process that produces a greater growth in the total number of cells that a plant has. Polyploidy gives rise to some consequences in plants, for example, cell size increases and their development becomes slower , generally the size of the seeds is larger, and their germination it is slowed down, being lower than that of diploid organisms.

Plants with polyploidy are known by the name of giga , because they are larger in size. Its life cycle is longer and its flowers are also larger than the original plants, they better resist adverse weather conditions , pests and diseases .

Advantage

Some advantages of polyploidy are as follows:

• Their cells are larger reason produce leaves and fruits more large .
• Polyploid plants have higher hybrid vigor than diploid plants.
• Helps mitigate genetic disorders .
• Helps plants overcome normal barriers that prevent self-fertilization .

Disadvantages

Some of the disadvantages that can occur in polyploid organisms are:

• Changes in cell architecture and regulatory implications due to the increase in the genomic content of an organism that produces a change in the relationship between the three-dimensional and two- dimensional components of the cell.
• Difficulties in mitosis since polyploidy is a problem for the normal completion of mitosis and meiosis, and this can lead to the production of aneuploid cells .
• Difficulties in meiosis since this process involves three or more sets of chromosomes that can also produce aneuploids , depending on the frequency and form of the aneuploid production on the type of polyploidy.
• Regulatory changes in gene expression .

Importance of polyploidy

Polyploidy is associated with major evolutionary transitions , advances in the development and the adaptive radiation of species. Genomic duplication doubles the amount of genetic material for evolution and the functional divergence that duplicated genes possess is very important for the biological evolution of plants and animals.