Why does meiosis appear to require DNA replication?

[kotreny]

The purpose of meiosis is to create genetic variation unattainable through mitosis by, in effect, randomly replacing one homolog from each homologous chromosome pair with another one from a different individual. There is also an exchange of genes between homologs before this replacement occurs, generating even more variation. Variation, of course, is a favorable trait.

To achieve the results of meiosis, it is necessary to separate the two members of every homologous pair, so that each set of homologs may end up in a gamete ready to combine with another. This occurs in meiosis I. For crossover, it is necessary to place the homologs closely adjacent to each other, so that they may form chiasmata prior to anaphase I. This, too, occurs in meiosis I.

What I don't understand is where DNA replication comes into this. As a result of sister chromatid formation earlier in S phase of the cell cycle, meiosis is forced to proceed with a second phase, meiosis II, in which the sisters are pulled apart like in mitosis.

This brings me to my question: Does chromosomal duplication have any role whatsoever in producing the positive results--with respect to evolution--of meiosis? Or is it merely a vestige of mitosis, which I suppose meiosis evolved from? My guess is that S phase in cells destined to produce gametes is simply an evolutionary artifact of mitosis, and that S phase was not disposed of because then the cell would have to produce two signals (or one long-lasting signal) in order to both cancel S phase and differentiate meiosis from mitosis. This, I suppose, is harder than generating only one quick signal to initiate meiosis as we know it, even though this form of meiosis involves processes that might otherwise be superfluous.

Thanks in advance for any replies, even if only a simple affirmation of what I've written.

 

[mishrashubham]

This might help

https://www.physicsforums.com/showthread.php?t=246907

 

[kotreny]

Thanks, mishrashubham, that was helpful. So this exact same question has been asked before. Near the end they started mentioning what was essentially a more general version of my guess, corroborating my thoughts.

I can't imagine how you found that thread, save for having read it when it was still fresh back in 2008. Google? Forum search? If there's any special trick to finding threads on a topic you want, let me know and I'll be grateful. Or was it a serendipitous combination of keywords?

 

[mishrashubham]

Haha no magic tricks there. Just scroll down and you'll find the thread in the "Similar threads" Section. As for finding a thread before posting anything, a title search in biology forum with keywords 'meiosis' and 'replication' yields the same results.
https://www.physicsforums.com/search.php?searchid=2606777

A very interesting question that you have put forward by the way; since it makes sense to just crossover and produce two gametes instead of replicating and then crossing over to produce four. But probably as already mentioned in the thread, this has remained because of meiosis evolving from mitosis and this extra step not posing any particular disadvantages to its bearer.

 

[LudusRex]

I can provide some insight into why DNA replication is necessary for meiosis to occur. Meiosis is a specialized form of cell division that occurs in reproductive cells, such as sperm and egg cells, in order to produce gametes with half the number of chromosomes as the parent cell. This is essential for sexual reproduction and creating genetic variation in offspring.

DNA replication is necessary in meiosis because it ensures that each gamete receives a complete set of genetic information. Without DNA replication, the resulting gametes would only have half the genetic information needed for proper development and functioning. This would lead to genetic disorders and potentially hinder the survival of offspring.

In meiosis, DNA replication occurs during the S phase of the cell cycle, before the cell divides into two daughter cells. This is important because it allows for the formation of homologous pairs of chromosomes, which are necessary for crossover and exchange of genetic material during meiosis I. Without DNA replication, the homologous pairs would not be able to form, and the resulting gametes would not have the necessary genetic variation.

Additionally, the process of DNA replication also plays a role in maintaining the integrity of the genetic information. Errors in DNA replication can lead to mutations, which can have negative effects on the offspring. Therefore, DNA replication is essential for ensuring the accuracy and fidelity of genetic information in meiosis.

In conclusion, DNA replication is a crucial step in meiosis as it allows for the formation of homologous pairs and ensures the proper distribution of genetic information to the resulting gametes. It is not simply a vestige of mitosis, but a necessary process for the success of meiosis and the evolution of genetic diversity in offspring.