The 5 Differences Between Haploid And Diploid Cells
The cell is the morphological and functional unit of the living being. Every living entity, from the most basal bacteria to the human being, has at least one cell capable of self-replication and exchanging substances with the environment. Prokaryotic living beings have only one cell that makes up their entire body, but eukaryotes can integrate billions of them into our organism, each one in a system much larger than the unit and with marked functionality.
As we have said, the cellular entity is equivalent to life. The only organisms that fit this premise are viruses, viroids and prions, but they are rarely considered living beings. Rather, they constitute a separate group of pathogenic biological agents with infectious potential. Without the cell, the minimum requirements for life to develop as such are not met.
In any case, it should be noted that, for example, within humans there are 2 large cell types: haploid and diploid. In the following lines, we tell you the differences between haploid and diploid cell and its evolutionary significance.
What are the differences between haploidy and diploidy?
In nature, no adaptation has developed by chance. Every characteristic serves (or has served) a purpose in the evolutionary history of the species, so the fact that haploid and diploid cells exist within the same organism must have a reason for being. In the following points, we explore it.
1. Haploid cells only contain one set of chromosomes, diploid cells contain two.
This is the main difference between haploidy and diploidy. A diploid cell (2n) contains inside its nucleus a set of paired chromosomes, in which all the genetic information is found of the individual, half of the father and half of the mother. In the case of humans, there are 23 pairs of chromosomes, 22 autosomal and one sexual (XX and XY), which encompass around 25,000 different genes. Of the 46 total chromosomes that exist within the cell nucleus, 23 come from one parent and 23 from the other.
On the other hand, a haploid (n) cell is one that contains only one chromosome of each type. In the case of human gametes (eggs and sperm), the cell nucleus only contains 23 chromosomes. The explanation is simple; If each gamete were diploid, in the union to form the zygote the resulting cells would have more and more chromosomes:
Thus, if haploid cells did not exist during sexual reproduction, in just 3 generations a human being would go from having 46 chromosomes (23 x 2) to 184 (23 x 8). The duplication of a single chromosome when it does not touch can already be fatal, so this mechanism of genetic accumulation would be incompatible with life.
2. Diploid cells divide by mitosis, and haploid cells by meiosis
As we have already established, a somatic diploid cell (which makes up tissues) has a pair of each chromosome, each being a member of one of the two parents.
Since these cells are not involved in reproduction (they are only intended to maintain and repair body structures), they have no need to divide their genetic information in half Therefore, they divide by mitosis, a process in which a mother cell gives rise to two exactly identical daughter cells, through the duplication of its DNA and the partition of the cytoplasm.
As you may suspect, the case of haploid cells is completely different. In the human body, these cellular units are the eggs and sperm, those responsible for fertilization to occur. For diploidy to remain in the zygote, each pair of chromosomes must be “split” in half and left with only one of the two members, as we have seen in the previous section.
So that, The process of formation of a haploid cell is much more complex than that of a diploid (at least within a diploid organism). To exemplify it, we show you the synthesis process of a sperm:
Thus, 4 haploid gametes are produced where there was previously a diploid germ stem cell Furthermore, throughout this process, crossovers and chromosomal permutations occur, which mean that the parental information is not presented in the same way in the offspring. For this reason, it is said that sexual reproduction is the basis of genetic diversity in species.
3. Haploidy and diploidy are restricted to different cell groups
All the cells that make up our body are diploid, except for the gametes (eggs and sperm), which are synthesized in the egg and testicle, respectively. Thus, it is generalized that human somatic cells are diploid and sexual cells are haploid.
Still, this is not entirely true: e.g. Most hepatocytes (liver cells) are tetraploid, meaning they contain twice as much genetic information as a normal somatic cell There are always exceptions that prove the rule.
4. Diploidy allows the differentiation of sexes in some species
In the colonies of eusocial insects such as bees, wasps and ants (Hymenoptera), the males are haploid (X) and the females are diploid (XX). This evolutionary strategy follows a clear pattern: males can be born from a fertile female without the need for her to have been previously fertilized, which greatly facilitates the reproductive period between colonies of the same population.
As you can imagine, in humans this is not the case at all, since both males (XY) and females (XX) are diploid. In any case, it is interesting to know that haploidy codes for males in some species of the animal kingdom
In the human body, the functionality of diploid cells is to keep the body’s biological system afloat. For example, the somatic cells of the dermal and epidermal layers are in continuous growth, as about 40,000 keratinocytes (cells from the stratum corneum, the most superficial) are shed every minute of our lives. Division by mitosis promotes the restoration, maintenance and replacement of all body tissues.
On the other hand, haploid cells have a functionality already explored: sexual reproduction Although sexual reproduction is much more expensive than simple mitosis, it makes great evolutionary sense. All the descendants of a lineage divided by mitosis are genetically the same, so they have the same aptitudes in the face of environmental changes and their range of adaptive capacity is minimal.
On the other hand, species that follow a pattern of sexual reproduction present very different specimens within the same population at a genetic level, since a child is never the same as one of its parents, but rather a combination of both (more mutations and crossings). . Thus, The existence of haploid cells and the formation of gametes is what generates the diversity of the planet throughout generations in addition to adaptive capabilities.
Summary
As you have seen, the differences between haploid cells and diploid cells go far beyond chromosome endowment. It is essential to know the variations between cellular entities at a microscopic level, but also to apply it in a medical and evolutionary field.
Both cell types are two essential pieces in the same gear: diploidy maintains life, while haploidy generates it. Both processes are vital for the maintenance of species that reproduce sexually.
