• What is cell reproduction?
• Types of cell reproduction
• Importance of cell reproduction
• Phases of mitosis
• Phases of meiosis

We explain what is cell reproduction, meiosis, mitosis and its phases. Also, its importance for the diversity of life.

Cellular reproduction allows the existence of organisms.

What is cell reproduction?

It is known as cell reproduction or cell division to the stage of cellular cycle in which each cell divides to form two distinct daughter cells. It is a process that occurs in all forms of life and that guarantees the perpetuity of their existence, as well as growth, tissue replacement and reproduction in the multicellular beings.

The cell is the basic unit of life. Each cell, like living things, has a weather of life during which it grows, matures and is play and dies.

There are various biological mechanisms of cell reproduction, that is, they allow the generation of cells new, replicating their Genetic information and allowing the cycle start over.

At a certain point in the lives of living beings, your cells stop reproducing (or begin to do so less efficiently) and begin to age. Until that happens, cell reproduction has the purpose of maintaining or increasing the number of cells that exist in an organism.

In the single-celled organisms, cell reproduction creates a organism totaly new. This generally occurs when the cell has reached a certain size and volume, which tend to decrease the effectiveness of its nutrient transport processes and, thus, the division of the individual is much more effective.

Types of cell reproduction

In principle, there are three main types of cell reproduction. The first and the simplest is the Binary fission, in which the cellular genetic material replicates and the cell proceeds to divide into two identical individuals, just as the bacteria, endowed with a single chromosome and with processes asexual reproduction.

However, more complex beings, such as eukaryotes are endowed with more than one chromosome (such as Humans, for example, that we have a pair of chromosomes from the father and one from the mother).

More complicated processes of cellular reproduction apply in eukaryotic organisms:

• Mitosis. It is the most common form of cell division in eukaryotic cells. In this process, the cell replicates its genetic material completely. To do this, he uses a method of organizing chromosomes in the equatorial region of the cell nucleus, which then proceeds to divide in two, generating two identical chromosomal endowments. The rest of the cell then proceeds to duplicate and slowly cleave the cytoplasm, until the plasma membrane it ends up dividing the two new daughter cells in two. The resulting cells will be genetically identical to their parent.
• Meiosis. It is a more complex process, which produces haploid cells (with half the genetic load), such as sex cells or gametes, endowed with genetic variability. This occurs in order to provide half of the genomic load during fertilization, and thus obtain genetically unique offspring, avoiding clonal (asexual) reproduction.Through meiosis, a diploid cell (2n) undergoes two consecutive divisions, thus obtaining four haploid daughter cells (n).

Importance of cell reproduction

Cell division creates colonies of unicellular organisms, but above all it allows the existence of multicellular organisms, made up of differentiated tissues. Each tissue suffers damage, ages and eventually grows, requiring replacement cells for old or damaged ones, or new cells to add to the growing tissue.

Cell division enables both the growth of organisms and the repair of damaged tissues.

On the other hand, disordered cell division can lead to diseases, in which this process occurs uncontrollably, threatening the life of the individual (as occurs in people with cancer). That is why in modern medicine the study of cell division is one of the key areas of scientific interest.

Phases of mitosis

Mitosis involves a complex series of changes in the cell.

In cell reproduction of the mitosis type, we find the following phases:

• Interface. The cell prepares for the process of reproduction, doubling its DNA and taking the pertinent internal and external measures to successfully face the process.
• Prophase. The nuclear envelope begins to break down (until it gradually dissolves). All genetic material (DNA) condenses and forms chromosomes. The centrosome duplicates and each moves to one end of the cell, where microtubules are formed.
• Metaphase. Chromosomes line up at the equator of the cell. Each of them has already been duplicated at the interface, so at this point the two copies are separated.
• Anaphase. The two groups of chromosomes (which are identical to each other) move away thanks to the microtubules towards the opposite poles of the cell
• Telophase. Two new nuclear envelopes are formed. Microtubules disappear.
• Cytokinesis The plasma membrane strangles the cell and divides it in two.

Phases of meiosis

In meiosis a cell produces four cells, each with half the chromosomes.

In type reproduction meiosis, then proceed to a new bipartition of the daughter cells, thus obtaining four haploid cells.

Meiosis involves two distinct phases: meiosis I and meiosis II. Each of them is composed of several stages: prophase, metaphase, anaphase and telophase. Meiosis I is distinguished from meiosis II (and mitosis) because its prophase is very long and in its course homologous chromosomes (identical because one comes from each parent) pair and recombine to exchange genetic material.

Meiosis I. Known as the reductive phase, it results in two cells with half the genetic load (n).

• Prophase I. It is composed of several stages. In the first stage, DNA is condensed into chromosomes. The homologous chromosomes then pair up forming a characteristic structure called the synaptonemic complex, where crossover and gene recombination occurs. Finally, the homologous chromosomes separate and the envelope of the core disappears.
• Metaphase I. Each chromosome, made up of two chromatids each, lines up on the median plane of the cell and binds to the microtubules of the achromatic spindle.
• Anaphase I. Paired homologous chromosomes separate and move to opposite poles. Each pole receives a random combination of maternal and paternal chromosomes, but only one member of each homologous pair is present at each pole. Sister chromatids remain attached to their centromeres.
• Telophase I. One of each pair of homologous chromosomes is at each pole. The nuclear membrane is formed again. Each nucleus contains the number of haploid chromosomes, but each chromosome is a duplicated chromosome (consisting of a pair of chromatids). Cytokinesis occurs, resulting in two haploid daughter cells.

Meiosis II. It is the duplicative phase: cells from meiosis I divide, resulting in DNA duplication.

• Prophase II. Chromosomes condense. The core envelope disappears.
• Metaphase II. Chromosomes line up on the mid-planes of your cells.
• Anaphase II. The chromatids separate and move towards opposite poles.
• Telophase II. The chromatids that reach each pole of the cell are now the chromosomes. Nuclear envelopes re-form, chromosomes gradually elongate to make chromatin fibers, and cytokinesis occurs. The two successive divisions of meiosis produce four haploid nuclei, each with one chromosome of each type. Each resulting haploid cell has a different combination of genes.