Occurs in organisms that sexually reproduce ==> Occurs in meosis.
Meiosis is a type of gamete-specific nuclear division.
Meiosis occurs during spermatogenesis and oogenesis (egg formation in women).
In order for the number of chromosomes, characteristic of the species, to be conserved, it is necessary that before the encounter, the number of chromosomes of each of the reproductive cells be divided by two.
The reduction in the number of chromosomes takes place during the phenomenon called "meiosis".
Occurs during growth and development ==> It concerns mitosis.
Mitosis will ensure the good fulfillment of several phenomena:
. embryonic development,
. the general growth of organisms from birth to adult size,
. continued growth of certain organisms and / or organs; for example, trees, hair, teeth in ruminants, nails, ...
The DNA is replicated ==> concern both mitosis and meiosis.
The cell cycle of eukaryotic cells is as follows:
• Interphase (normal functions, DNA replication)
G1 - growth / cellular activity
S - DNA synthesis / replication
G2 - preparation for division
• Phase M (cell division): which consists of either mitosis or meiosis, depending on cell types.
• Cytocinesis (cytoplasmic division).
So whether it is mitosis or meiosis, both are preceded by a replication of the genetic material (DNA)
Occurs in all organisms ==> concern both mitosis and meiosis.
An organism is a set of elements that make up a functional structure.
In biology, the term organism designates a living being as it is organized, that is to say composed of different organs or organelles forming a coherent whole (as opposed to micro-organisms).
All multicellular organisms have sexual reproduction, so their cells are systematically mitosis and meiosis.
We exclude microorganisms of which a very small part of them have asexual reproduction.
The number of chromosomes remains the same : concerns only mitosis.
During mitosis, the human cell has 2n monochromatid chromosomes. In phase S consists of a doubling of the amount of DNA indeed, and the cells then have 2n chromosomes bichromatidiens. In the metaphase of mitosis, the chromosomes of the mother cell are arranged on a "metaphase plate", then split in 2-chromosomes, but monochromatids, during anaphase. Each daughter cell therefore has 2n monochromatid chromosomes.
The number of chromosomes reduces by half ==> Concerns only meiosis
Meiosis unfolds in two stages:
* The first meiotic division is called reductional because it allows to pass from 2n double chromosomes to n double chromosomes.
* The second is called equational because it preserves the number of chromosomes: one passes from n double chromosomes to n simple chromosomes.
Meiosis thus allows the formation of 4 haploid daughter cells (or gametes).
In humans, a normal cell contains 2n = 46 chromosomes (thus 23 pairs) while a gamete contains n = 23 chromosomes in two divisions).
