Discussion of all aspects of cellular structure, physiology and communication.
Mitosis happens in all body cells. It consists of one division. The cell forms its 2 identical daughter cells.
Meiosis happens in gametes. (reproduction cells). It consists of 2 divisions. The cell forms 4 different cells. The main difference is: the daughter cells have half the number of chromosomes that the first cell has.
Have a look at these (and then please dont hesitate to ask if something is not clear):
http://courses.washington.edu/bot113/Sp ... IS_AND.pdf
And you can have a quick practice with this:
So in meiosis the number of chromasomes is halfed because it needs to combine with another cell contining the same number of chromasomes to form an embryo thus resulting in an embryo with the correct number of chromasomes???
Yes that is why meiosis creates haploid cells
No, We all have two sets of identical chromsomes,meiosis first halves these pairs of chromosomes, and mixes them a little for genetic variation. This creates 2 cells with half the chromosomes. It is now when each of these two cells do the 'mitosis like' division to create the 4 gametes.
For simplicity yes we can say they are like same. But actually they are not. because, in meiosis there is a process called crossing-over.
Hi I am a new member, and I am having some Meiosis/Mitosis problems too...
when the chromosome division is completed in anaphase, are the resulting one-chromatid chromosomes considered full fledged chromosomes? If so, does that mean that after telophase and cytokinesis that S-phase (or some other phase of the cell cycle) replicates the other chromatid? This would lead me to belive that a two chromatid chromosome is in essence two of the same sister chromatid... It just confuses me when I see one chromatid chromosomes at the end of mitosis..... Thanks!
No, all chromosome replication occurs BEFORE Mitosis (M phase) in S phase. Chromosome just means colored body and I'm not a fan of the term at all since it gets tossed into all sorts of places and just confuses the heck out of people. Its better to think of the X-shaped thing as sister chromatids. Each is an exact copy of the other and when the separate in early anaphase they are known as daughter chromatids.
Lets take a random human cell as an example. In S phase the cell repicates all of its genome and in essance becomes 4n for a short period of time. When the cell divides in M phase, each cell is 2n automatically, with no replication needed. Remember that the X-shape is not the usual state of the genome.
Hope this helps.
This is a common point of confusion for many people actually, so hopefully I can try and explain this well.
It may first be helpful to identify during which situations mitosis and meiosis are used.
First off, asexual organisms use mitosis to reproduce. By asexual we mean basically "cloning" - daughter cells are genetically identical to the original cell. Meiosis is used for sexual reproduction, which results in an individual producing a gamete that is haploid (half the number of that of a diploid via mitosis).
Mitosis is probably easier to understand, but without pictures it may be hard to explain.
Mitosis is divided into various phases just like meiosis: I have only highlighted the major steps in each phase, there are other things also going on with microtubules and kinetochores that are also involved.
In humans we use meiosis to produce gametes, gametes are just sperm or egg. A sperm is needed to fuse with an egg to produce a zygote. The zygote has 2N, just like its parents. Without meiosis zygotes would have 4N, which would spell bad news for the developing embryo.
Sexual reproduction is advantageous over asexual reproduction in the sense that it produces genetic variation through recombination (crossing over). However, asexual reproduction is favorable in systems that are not prone to disease, mutation, or when an individual wants to pass their entire genome (not only half) to its offspring.
Prophase: nuclear envelop disappears. Prior to prophase chromosomes replicate (interphase). Chromosomes are "random" with respect to each other in cell.
Metaphase: chromosomes line up on the metaphase plate. They form a line right down the middle of the cell, preparing for anaphase.
Anaphase: microtubules pull homologous chromosomes apart to the poles.
Telophase: cell division occurs. You now have two identical cells and replication repeats itself, starting prophase again.
In meiosis, the same basic concepts apply, but they are divided into two different portions of the cycle, M1 and M2. M1 is the reduction division, it reduces the ploidy from 2N to 1N. There is also M2 which then pulls apart sister chromatids from homologous chromosomes.
In all honesty, I think you are far better off going to a site or tutorial that has pictures, it is really the best way to visualize this. Text alone isn't going to do much.
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