The 7 differences between haploid and diploid cells
The cell is the functional unit of life. The simplest degree of organization of organic matter that can guarantee the fulfillment of vital functions. And the human body, for example, is the result of "simply" the union of 30 million million cells.
And if each of these cells is a piece in the puzzle of our body, it is thanks to genetic material. To the 30,000 genes that, organized in chromosomes, make it possible to encode for the synthesis of all those proteins that make it possible for the cell to fulfill its physiological functions and that, ultimately, our body functions as a perfectly oiled machine.
And, in reference to these chromosomes, the highly organized structures of DNA and proteins that contain most of our genetic information, we have heard many times that our genome is made up of 23 pairs of chromosomes. 46 in total.
But this is not entirely true. In Biology, there are no black and white. There are grays. Nuances that show us that everything that has to do with genetics is subject to changes that, in reality, make evolution possible. And in this sense, today we come to talk about the differences between two very important types of cells: haploid and diploid.
What is a haploid cell? And a diploid cell?
Before looking at their differences in the form of key points, it is interesting (but also important) that we define both concepts individually. And it is so, understanding exactly what haploidy and diploidy consist of, that the differences between haploid and diploid cells will begin to become much clearer.
Haploid cell - what is it?
A haploid cell is one that has a genome made up of a single set of chromosomes. In other words, compared to a diploid cell (which we will analyze later), it has half as many chromosomes. Haploidy, then, is the cellular state in which the nucleus does not have a double chromosome endowment.
It is common to refer to haploid cells with the following nomenclature: n. Where (n) refers to the number of chromosomes and, as we can see, it is not multiplied by any numerical value. In the human species, n = 23. And the haploid cells of our body (which we will now see what they are) thus have a chromosomal endowment of just 23. There is only one copy of each chromosome.
Algae, fungi (asexual), bryophytes, and protozoa are made up of haploid cells. Similarly, male bees, wasps, and ants are also haploid organisms, in which case, as we will see later, haploidy is a strategy for differentiation of the sexes.
Be that as it may, humans and the vast majority of animals are not haploid. Does this mean that they do not have haploidy in any cell? No. Not much less. Sex gametes (sperm and eggs) are haploid. And this is necessary, because when they come together, a diploid cell is obtained that will allow the development of a fetus also based on diploidy (n + n = 2n).
Haploid cells, although they can be obtained by haploid stem cell mitosis, usually have a genesis based on meiosis, cell division that takes place only in germ cells with the aim of reducing the chromosomal endowment, performing genetic recombination and thus obtain haploid gametes with genetic variability.
In summary, haploidy is a cellular state of haploid cells, those cells that, in the human species, are limited only to sperm and ovules, are obtained through a process of meiosis and that, above all, they have the characteristic of having a single set of chromosomes. They have half the chromosomal endowment compared to the diploids that we will now analyze.
Diploid cell: what is it?
A diploid cell is one that has a genome made up of two sets of chromosomes. In other words, compared to a haploid cell, it has twice the number of chromosomes. Diploidy, then, is the cellular state in which the nucleus has a double chromosome endowment.
It is common to refer to diploid cells with the following nomenclature: 2n. Where (2n) refers to the number of chromosomes and, as we can see, it is multiplied by a numerical value: 2. In the human species, as we have seen, n = 23. Therefore, the diploid cells of our body have a chromosome endowment of 46 (2 x 23). There are two copies of each chromosome.
Human beings, like the vast majority of animals and plants, are organisms based on diploidy. This means that almost all of our cells (except gametes) have a double chromosome endowment. Somatic cells (all cells in an organism except gametes) are diploid.
Skin cells, muscle cells, bone cells, kidney cells ... All our cells, except gametes, are diploid. They are 2n. They have two sets of chromosomes. And, in this sense, the genesis of diploid cells is based on mitosis, a cell division that consists of dividing a stem cell into two daughter cells that not only have the same number of chromosomes (2n), but the same (or almost the same, because random mutations always come into play) genetic information.
In summary, diploidy is a cell state of diploid cells, those cells that, in the human species, make up the group of somatic cells (all except sperm or ovules), which are obtained through a process of mitosis and that, above all, they have two sets of chromosomes. They have twice the chromosomal endowment compared to the haploids that we have seen before.
How are haploid cells and diploid cells different?
After defining both concepts, it is sure that it has become more than clear how haploidy and diploidy differ. Still, to give you the most concise information, we have prepared a selection of the main differences between haploid and diploid cells in the form of key points. Let's go there.
1. Diploid cells have twice as many chromosomes as haploid cells
The most important difference. While haploid cells are (n), diploid cells are (2n). While haploid cells have only one set of chromosomes, diploid cells have two sets. While haploid cells have only one copy of each chromosome, diploid cells have two. That is, haploid cells have half the chromosomes compared to diploid cells. If a human diploid cell has 46 chromosomes, a haploid cell has 23.
2. Diploid cells are obtained by mitosis; haploids, by meiosis
As we have seen, although haploids can be obtained through mitosis of haploid stem cells, the most common is that their genesis is based on meiosis, a type of cell division that takes place in germ cells and has the objective of both reducing the chromosomal endowment (going from 2n to n) and carrying out genetic recombination, in order to obtain haploid gametes (sperm or ovules) with genetic variability.
The genesis of diploid cells, on the other hand, is based on mitosis, the other great type of cell division that all somatic cells in our body follow and that consists of dividing a stem cell into two daughter cells that not only have the same number of chromosomes (2n), but the same (or almost the same, because random genetic mutations always come into play) information on these chromosomes. There has been no recombination, unlike what happened in meiosis.
3. Somatic cells are diploid; gametes, haploid
Focusing on the human species, all cells in our body, except gametes, are diploid. That is, with the exception of sperm and eggs, all the other cells in our body (called somatic or autosomal) have two sets of chromosomes (2n). In gametes, it is necessary that they only have one set (n), because during fertilization, two gametes must fuse to obtain a diploid cell that will give rise to a diploid organism.
4. Animals and plants are diploid; algae and fungi, haploid
In the vast majority of animals (including humans, of course) and plants, the natural tendency is diploidy. As a general rule, with the exception of cells associated with sexual reproduction, the animal and plant cells are diploid. In contrast, algae, fungi (asexual), bryophytes, and protozoa are made up of haploid cells.
5. Haploidy allows sex differentiation in some species
As we have said, the vast majority of animals are diploid in their somatic cells. But that means there are exceptions. This is the case of male bees, wasps and ants. The males of these species are haploid (X) and the females, diploid (XX). This allows not only the differentiation of the sexes, but that males can be born from a female without the need for it to have been fertilized. The haploidy-diploidy game is a clear evolutionary strategy.
6. Two haploid cells can fuse to form a diploid cell
The birth of a human being has its most fundamental origin in fertilization. In the fusion of a haploid male sex gamete (sperm) and a haploid female sex gamete (ovum). After this fusion of their nuclei, a diploid cell is obtained that, after millions of divisions, will give rise to a human being. Obviously, n + n = 2n. And here is the miracle of life.
7. Diploid cells maintain biological functions; haploids, make sexual reproduction possible
Somatic cells (of the skin, blood, bones, muscles, kidneys, etc.) are all diploid (except for those of the liver, which are tetraploid, with four sets of chromosomes). This means that diploid cells, being the units of our organs and tissues, have a clear function of maintaining the physiology of the organism. Haploids, on the other hand, being sexual gametes, do not maintain biological functions, but they do make sexual reproduction possible, being those that are involved in fertilization.