A recent article in the journal PLOS Biology discusses how some species use both mitosis and meiosis to produce offspring. This is a fascinating topic that deserves more attention, so we at Fitly Strongly will write about it!
The authors of the article argue that most species use only mitosis to produce offspring, but some species, including fungi, plants, and animals such as worms and butterflies, use both mitosis and meiosis.
Why do some species employ both mitosis and meiosis, whereas other species use only mitosis? What are the evolutionary pressures that cause one sort of reproductive strategy to replace another? These are the questions asked by the authors.
Read on to learn more about this topic. If you find this information interesting or important, please share this article with your friends and family.
Meiosis reduces genetic variation
While mitosis keeps genetic variation intact, meiosis — the division of cells that results in offspring cells with half the number of genes of their parent cell — reduces genetic variation.
This happens in two ways. First, when an egg and sperm fuse during fertilization, they have only half the number of genes of a mature cell. Second, when a mother cell divides to produce eggs or embryos through mitosis, these offspring cells all have the same number of genes as their mother cell.
Over very long periods of time, this can lead to a reduction in the variety of traits present in a species — which can make it more vulnerable to environmental changes and extinction. Species that rely exclusively on mitosis for cell division may be at greater risk for these reasons.
Some research suggests that meiosis may have evolved as early as 1 billion years ago, which was roughly when the first eukaryotic cells appeared. These eukaryotic cells had a nucleus enclosing DNA and associated proteins such as RNA polymerase needed for gene expression.
Mitosis produces genetically identical offspring
As mentioned earlier, meiosis produces gametes, the reproductive cells that fuse during sexual reproduction. During meiosis, chromosomes are duplicated and then divided into separate daughter cells.
Some species can only produce offspring via meiosis, whereas other species only use mitosis to produce offspring. The reason for this distinction is not entirely known, but there are some theories.
One theory is that some species may have evolved from a haploid organism (one cell) to a diploid organism (two cells) via meiosis. Over time, the organism may have lost the ability to undergo meiosis due to lack of need for it.
Another theory is that some species may have evolved from an asexual organism via mitosis. Over time, the ability to undergo meiosis may have emerged due to sexual competition or selection for higher quality offspring.
Mitosis increases genetic variation
As mentioned before, mitosis is the process of cell division that produces cells with the same genetic content. This process is essential for growth and development of all living organisms.
However, some species use mitosis during all stages of their life cycle, while other species only use it during the early stages. Why is this?
As described by biologists, a species that only uses mitosis during early stages of development may eventually transition to meiosis. This happens because meiosis produces gametes with different genetic content, which can be more beneficial later in the life cycle.
For example, consider a common seaweed that uses only mitotic division during its early stages of development. Once it becomes mature enough, it can transition to the stage where it uses meiosis to produce different gametes. These gametes will then have different genetic content than the earlier cells did.
Species with large populations tend to use meiosis more often
As explained earlier, meiosis is the process that produces gametes with only one set of chromosomes, and mitosis produces cells that have two copies of each chromosome.
However, some species use both meiosis and mitosis to produce offspring. This is most common in species with large populations. How does this make sense?
For example, imagine a very large population of grasshoppers. If every individual only had to produce one offspring via meiosis, then it would take a very long time for the population to replenish itself.
There would be a lot of wasted time waiting for all of the other individuals to produce an offspring! By employing both meiosis and mitosis, more offspring can be produced more quickly.
This helps prevent population decline due to lack of reproduction, which is a helpful strategy in unpredictable environments.
Species with small populations tend to use meiosis more often
A small population size can result from a small initial population or a decrease in population size over time.
A small initial population may be the result of a lack of fertilized eggs that develop into adults, or it may be the result of there being few offspring that survive to adulthood.
If an organism only reproduces once during its life, then meiosis is the most cost-effective way to produce offspring. By dividing its DNA into identical copies, meiosis produces two new individuals that each have half of the parent’s genetic information.
However, if an organism can repeatedly reproduce, then employing only mitosis is more efficient because it does not take as much time. As a species’ population size grows, more individuals are born and more offspring are produced each time an individual reproduces. This means there are more offspring to care for and raise to adulthood.
The size of the offspring affects which type of cell division is used
When the offspring is too large to be produced by a single cell, meiosis is used to produce the next generation. This ensures that there is genetic diversity in the next generation.
Both meiosis and mitosis have their advantages and disadvantages. Some species employ both in order to maximize their fitness in a changing environment.
The environment affects which type of cell division is used
As mentioned before, meiosis is the process that decreases the number of chromosomes in a cell and divides the cell into two distinct cells. This process occurs in sex cells, or gametes.
However, some species have both meiotic and mitotic cells in the same organism. This happens in two ways: first, some species have both asexual and sexual populations within it; second, some species have both meiotic and mitotic cells within it.
A common example of the first is slime molds. These have a phase where they do not employ meiosis, but instead use mitosis to create new cells. These new cells then go through a process called convergent division where they resemble eggs, before developing into more non-sexed cells.
An example of the second is liver flukes that live in marine mammals such as whales and seals. These parasites can switch between meiosis and mitosis depending on what kind of cell they need to infect.
Some species have switched between using mitosis and meiosis
As mentioned before, meiosis is the process that creates diversity within a species. This happens when chromosomes are separated and then paired with different chromosomes to create new combinations.
Some species have only used meiosis in their reproductive processes, whereas other species have also used mitosis to some extent. Some believe this may be due to how efficient meiosis is compared to mitosis.
It is more costly for a cell to divide its chromosomes and then recombine them than it is to just divide into two new cells. This makes meiosis more time-consuming than mitosis, but with better outcomes.
Because of this, some species may switch back and forth between the two based on time constraints due to mating schedules.