WHAT ARE DIPLOID CELLS? - BIOLOGY - 2025

The diploid cells are those containing a duplicate set of chromosomes. We call chromosomes that form pairs homologous chromosomes. Diploid cells therefore possess double genomes due to the presence of two complete sets of homologous chromosomes. Each genome is contributed by different gametes in the case of sexual reproduction.

As gametes are derived haploid cells, with chromosome content equal to 'n', when fused they generate diploid cells '2n'. In multicellular organisms, the initial diploid cell derived from this fertilization process is called a zygote.

Subsequently, the zygote divides by mitosis to give rise to the diploid cells that constitute the entire organism. One group of the body's cells, however, will be dedicated to the future production of haploid gametes.

Gametes, in an organism with diploid cells, can be produced by meiosis (gametic meiosis). In other cases, meiosis gives rise to the tissue, component or generation that by mitosis will give rise to the gametes.

This is the typical case of, for example, plants in which a sporophytic generation ('2n') and then a gametophytic ('n') occur. The gametophyte, a product of meiotic divisions, is responsible for producing the gametes, but by mitosis.

Apart from gamete fusion, therefore, the predominant way of generating diploid cells is by mitosis of other diploid cells.

These cells are the privileged site of gene interaction, selection, and differentiation. That is, in each diploid cell, the two alleles of each gene interact, each contributed by a different genome.

Advantages of diploidy

Living things have evolved to most efficiently prevail under conditions for which they can present a robust response. That is, to survive and contribute to the existence and persistence of a given genetic lineage.

Those who can respond, rather than perish, under new and challenging conditions take additional steps in that same direction, or even a new one. There are, however, changes that have resulted in major milestones in the diversification trajectory of living beings.

Among them are undoubtedly the appearance of sexual reproduction, in addition to the appearance of diploidy. This, from several points of view, confers advantages for the diploid organism.

We will talk a bit here about some consequences derived from the existence of two different, but related, genomes in the same cell. In a haploid cell, the genome is expressed as a monologue; in a diploid, like conversation.

Expression without background noise

The presence of two alleles per gene in diploids allows gene expression without background noise at a global level.

Although there will always be the possibility of being incapacitated for some function, a double genome generally reduces the probability of being incapacitated for as many as a single genome can determine it.

Genetic backup

One allele is an informational endorsement of the other, but not in the same way that a complementary DNA band is of its sister.

In the latter case, the support is to achieve permanence and fidelity of the same sequence. In the first, it is so that the coexistence of variability and differences between two different genomes allow the permanence of functionality.

Continuous expression

In a diploid organism the possibility of keeping active the functions that define and allow the information of the genome is increased. In a haploid organism, a mutated gene imposes the trait associated with its condition.

In a diploid organism, the presence of a functional allele will allow expression of the function even in the presence of a non-functional allele.

For example, in cases of mutated alleles with loss of function; or when functional alleles are inactivated by viral insertion or by methylation. The allele that does not suffer mutation, inactivation or silencing, will be in charge of the manifestation of the character.

Preservation of variability

Heterozygosity is obviously only possible in diploid organisms. Heterozygotes provide alternative information for future generations in the event of drastic changes in living conditions.

Two distinct haploids for a locus that codes for an important function under certain conditions will surely undergo selection. If you select for one of them (that is, for the allele of one of them), you lose the other (that is, the allele of the other).

In a heterozygous diploid both alleles can coexist for a long time, even under conditions not conducive to the selection of one of them

Advantage of heterozygotes

The advantage of heterozygotes is also known as hybrid vigor or heterosis. According to this concept, the sum of small effects for each gene gives rise to individuals with better biological performance as they are heterozygous for more genes.

In a strictly biological way, heterosis is the opposite counterpart to homozygosity - more interpreted as genetic purity. They are two opposite conditions, and the evidence tends to point to heterosis as a source not only of change, but also of better adaptability to change.

The value of recombination

In addition to generating genetic variability, which is why it is considered the second driving force behind evolutionary change, recombination regulates DNA homeostasis.

That is, the preservation of the informational content of the genome and the physical integrity of DNA depend on meiotic recombination.

Recombination-mediated repair, on the other hand, makes it possible to safeguard the integrity of the organization and content of the genome at local levels.

To do this, one must resort to an undamaged copy of DNA to try to repair the one that has suffered the change or damage. This is only possible in diploid organisms, or at least in partial diploids.

References

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