Compare the Similarities and Differences between Meiosis and Mitosis

Adrian Tam (G)

Purpose & Role:

Both mitosis and meiosis involve nuclear division that results in the formation of new cells for the creature. This is one of the seven characteristics of living being, the ability to reproduce. However, there are significant differences between the two types of division. Mitosis is used in asexual reproduction for growth, repair and replacement that contributes to the development of the organism. Meiosis, on the other hand, provides haploid gametes for sexual reproduction between two organisms, thus generate genetic differences between parent and offspring.

Products of the two types of division:

Mitosis allows the formation of two daughter cells that are genetically identical to the parent cell, with the same amount of chromosomes and identical genetic material. These daughter cells are clones to the parent cell. On the other hand, meiosis provides gametes that contain only half the number of chromosome number of an adult cell so that when gametes fuse together in fertilisation, a diploid zygote is formed. Genetic materials in daughter cells of meiosis are slightly different to adult cell due to variation from independent assortment and crossing-over of material.

Overview of different phases:

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Overview of different phases:

Both mitosis and meiosis consists of four main phases: prophase, metaphase, anaphase & telophase. For mitosis: During Prophase, nuclear membrane of parent cell disappears while DNA condenses to form two identical chromatids attached at the centromere. In Metaphase, Chromosomes lines up across the equator of cell with spindle apparatus attaching to the centromere. In Anaphase, separation of chromatids is achieved by the contraction of spindle apparatus, pulling chromosomes to opposite poles towards centrioles. In telophase, chromosomes diffuse into chromatin while nuclear membrane and nucleoli reforms. Meiosis also has all these four phases; however, these four phases happen twice in the process. Though meiosis-2 is exactly the same as mitosis phases, with the purpose to separate chromatids, meiosis-1 serves the purpose of separating homologous pairs of chromosomes. The only differences between meiosis-2 and mitosis are that four daughter cells instead of two are formed from meiosis-2 when they only have haploid number of chromosomes inside the cells. It is also to note that during prophase-2 of meiosis-2, centrioles move to opposite poles of the cells and spindle apparatus forms at right angle to that formed in prophase-1.

Meiosis-1:

Mitosis lacks the four phases that happens in meiosis-1, they are still called prophase, metaphase, anaphase and telophase. Prophase-1 is when homologous chromosomes pairs up as a bivalent as DNA condenses, while they tangle up and cross at chiasmata. This is also when material is exchanged between the chromosomes by crossing over to provide more genetic variation for offspring (mitosis lacks this phase, therefore the daughter cells from mitosis are clones of parent). In metaphase, divalent lines up along the equator with spindle apparatus attached to centromere. In anaphase, contraction of spindle fibres pulls homologous chromosomes to opposite ends of the cell. In telophase, nuclear membrane forms around each group of chromosomes with the centrioles divide into 2. Meiosis-2 then follows.

Variation in Meiosis:

As mentioned before, mitosis produces clones whereas meiosis produces haploid gametes with different genetic material as the parent. This introduces variation into a population, creating offspring different to parents. Therefore we cannot observe any mechanisms that bring variation in mitosis. In meiosis, variation is achieved by crossing over in prophase-1, when chromosomes tangle together and exchange of complementary alleles occurs, forming recombinants (combination of alleles are not in parents). Independent assortment also occurs when each pair of chromosomes orientates itself independently of every other pair at metaphase-1, making different combinations of information. This produces the raw material for natural selection, eventually leads to evolution – a change in a species over time. This does not happen in mitosis though.

Teacher Reviews

Here's what a teacher thought of this essay

Sam Morran

8th of Jan 2013

This is a very good essay. It has a good structure and uses the correct terminology when explaining the processes. However, the writer has misunderstood an area of both mitosis and meiosis and has not discussed replication of DNA. Whether replication occurs or not is the fundamental difference between the two processes and the resulting daughter cells - ie: how can you get 23 chromosomes from a cell with 46. I think that the writer has understood what they are discussing but has become a little bogged down with the writing - diagrams would have helped to alleviate this and given further clarity to the essay To extend this - some examples of where and how mitosis is beneficial would have been good and a greater link to variety and natural selection would have shown deeper understanding. ****

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Peer Reviews

Here's what a star student thought of this essay

groat

20th of Apr 2012

Quality of writing

This essay has a logical structure, progressing from an overview to specific details of mitosis and meiosis. Phrases such as "however" and "on the other hand" make a comparative piece much easier to follow, and the argument becomes much more convincing. All the technical terms are used correctly, so this essay would gain the quality of written communication marks. These are not awarded spelling, punctuation and grammar in Biology A-Level, but instead for terms spelt correctly and used in context with the question. I would've liked to have seen a diagram or two, especially as this was word processed.

Level of analysis

The level of analysis here is strong. There is a clear awareness of the purpose of each meiosis and mitosis, and the importance to living organisms. Technical terms such as haploid, diploid, gametes and zygote are used confidently. I would've liked to have seen a sentence saying how many cells meiosis results in, as this is mentioned for mitosis. A bit more direct comparison would help this. For example saying "Mitosis creates two cells, whereas meiosis creates four cells. The cells from mitosis are genetically identical, whereas crossing over means the meiosis cells are not" would ensure the direct comparison is there. Slightly out of context here, but examiners are keen to see comparative words such as "larger than" to ensure you understand the differences. Everything is covered to a good level of detail. The only thing I would add is mentioning that mutations may also cause changes in the number of chromosomes, or the DNA within.

Response to question

This essay approaches a comparison of meiosis and mitosis fairly well. Examiners are looking for a discussion around purpose, products and process, and this essay covers all of these points well. Scientific terms are abundant, and this is what will gain you marks in an exam. Many of the marking points are dependent on keywords, so this is a great example using them when necessary. I understand it's quite difficult to compare both processes without explaining them fully in turn, but learning key differences and similarities for the exam is the best way forward.

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