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Mendel’s Law of Segregation | Definition & Examples - Lesson | Study.com. (n.d.). study.com. https://study.com/learn/lesson/law-of-segregation-mendel-first.html

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(Mendel’s Law of Segregation | Definition & Examples - Lesson | Study.com, n.d.)

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Behavior of chromosomes during meiosis generate variation & exxplain Mendel's law of independent assortment.

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Behavior of chromosomes during meiosis generate variation & exxplain Mendel's law of independent assortment.

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Meiosis. (n.d.). The Cell Cycle. http://cycleofcells.weebly.com/meiosis.html

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Brookshire, B. (2019, December 6). Scientists say: mitosis. Science News Explores. https://www.snexplores.org/article/scientists-say-mitosis

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https://website-designer-2149.business.site/. (n.d.). Chromosomes and cell Division - Biology of humans. Educational Materials. https://schoolbag.info/biology/humans/27.html

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Byju’s. (2022, July 4). What Is the purpose of Meiosis I and II-. https://byjus.com/question-answer/what-is-the-purpose-of-meiosis-i-and-ii/

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Mitosis Images – Browse 11,257 stock photos, vectors, and video. (n.d.). Adobe Stock. https://stock.adobe.com/search?k=mitosis&asset_id=273158129

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(Mitosis Images – Browse 11,257 Stock Photos, Vectors, and Video, n.d.)

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What are the differences between meiosis I and meiosis II? | Socratic. (n.d.). Socratic.org. https://socratic.org/questions/5a6a2b7b7c0149646668ab98

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(What Are the Differences Between Meiosis I and Meiosis II? | Socratic, n.d.)

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How long does each of the stages in meiosis take? (n.d.). Biology Stack Exchange. https://biology.stackexchange.com/questions/76960/how-long-does-each-of-the-stages-in-meiosis-take

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(How Long Does Each of the Stages in Meiosis Take?, n.d.)

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How long are the phases of mitosis? | Socratic. (n.d.). Socratic.org. https://socratic.org/questions/how-long-are-the-phases-of-mitosis

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(How Long Are the Phases of Mitosis? | Socratic, n.d.)

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(269) Pinterest. (n.d.). Pinterest. https://www.pinterest.com/pin/400679698104511229/

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Earthhow. (2023, November 15). The 5 phases of Mitosis. Earth How. https://earthhow.com/mitosis-phases/

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Is meiosis a part of the cell life cycle? (n.d.). Quora. https://www.quora.com/Is-meiosis-a-part-of-the-cell-life-cycle

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(Is Meiosis a Part of the Cell Life Cycle?, n.d.)

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Technology Networks. (2022, October 7). Mitosis vs. Meiosis: Key Differences, Chart and Venn Diagram. Cell Science From Technology Networks. https://www.technologynetworks.com/cell-science/articles/mitosis-vs-meiosis-312017

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Title: Mitosis - Definition and Examples - Biology Online Dictionary. (n.d.). www.google.com. https://www.google.com/imgres?imgurl=https://www.biologyonline.com/wp-content/uploads/2020/04/mitosis-definition-and-examples.jpg&imgrefurl=https://www.biologyonline.com/dictionary/mitosis&h=1080&w=1920&tbnid=RzCmndD6UGZgMM&source=sa.im&tbnh=168&tbnw=300&usg=AI4_-kR8IvbPGSYJ4wFOuPcDSxBcWoKskw&vet=1&docid=TrLJKP4T4UOZyM

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(Title: Mitosis - Definition and Examples - Biology Online Dictionary, n.d.)

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Interphase--The centrosome is duplicated.

Prophase--Microtubules begin to form an early mitotic spindle between the duplicated centrosomes.

Metaphase--The two centrosomes are now located at opposite poles of the cell.

Anaphase--Microtubules emanating from the centrosomes shrink as the tension holding the chromosomes at the metaphase plate is broken by cohesin cleavage.

Telophase--The centrosomes remain segregated to opposite sides of the cell. Each daughter cell will receive one centrosome comprised of two centrioles.

Cytokinesis--Centrosomes signal to the cell that it is okay to proceed with cytokinesis. Research shows that cells where centrosomes are destroyed with a laser beam cannot undergo cytokinesis.

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Interphase--Are uncondensed but are still organized. The entire genome is replicated to create two identical semi-conserved copies of each chromosome.

Prophase--Condense. Duplicated chromosomes are called sister chromatids.

Metaphase--Align along the metaphase plate, the midpoint between the two centrosomes. Sister chromatids are joined at the centromere by proteins that form a structure called a kinetochore.

Anaphase--Cohesin is cleaved at the centromere of chromosomes, resulting in sister chromatids being pulled to opposite poles of the cell.

Telophase--Chromosomes begin to uncoil, becoming less condensed.

Cytokinesis--Chromosomes have returned to their interphase structure. This is a topic of much research, but it seems as though each chromosome occupies its own territory within the nucleus.

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In mitosis, cytokinesis does not always occur, some cells divide and are multinucleate, like muscle cells.

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In meiosis, cytokinesis must occur twice: once after telophase I and again, after telophase II.

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In anaphase of mitosis (and meiosis II), cohesin protein holding the centromeres of the sister chromatids together is cleaved, allowing the sister chromatids to segregate to opposite poles of the cell, at which point they are called chromosomes.

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In anaphase of meiosis I cohesin at the centromeres of the chromosomes is not cleaved and it therefore continues to hold sister chromatids together as the homologous chromosomes are segregated to opposite cell poles.

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In mitotic metaphase a single chromosome/ pair of chromatids line up along the metaphase plate.

Sister chromatids are identical and so the orientation of the chromosome doesn’t carry any meaning.

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In meiotic metaphase I pairs of homologous chromosomes line up along the metaphase plate.

The way in which the homologous pairs are oriented randomly with respect to the cell poles is referred to as the law of independent assortment and ensures a random and independent distribution of chromosomes to the daughter cells of meiosis I and ultimately to the haploid gametes at the end of meiosis II.

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Mitotic prophase is much shorter than meiotic prophase I.

There is no crossing over in mitosis.

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Meiotic prophase I is much longer that mitotic prophase.

During prophase I homologous chromosomes make contacts with each other called chiasmata and “crossing over” occurs. This is where chromosomes exchange sections of DNA. This is important for generating genetic diversity but is also crucial mechanically to hold homologous chromosomes together.

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In mitosis, prophase, metaphase, anaphase and telophase occur once.

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In meiosis, prophase, metaphase, anaphase and telophase occur twice. The first round of division is special, but the second round is more like mitosis.

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Example of a disease caused by an error in this process

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Example of a disease caused by an error in this process

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Errors in meiosis can lead to the wrong number of chromosomes ending up in germ cells, this is called aneuploidy. This can trigger miscarriage, but is occasionally tolerated. One example is Down’s syndrome, caused by trisomy 21. Another example is Klinefelter syndrome, where XY males have an additional X chromosome.

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Example of a disease caused by an error in the process

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Example of a disease caused by an error in the process

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Uncontrolled mitosis occurs in cancer, where either genes that stop cell division (tumor suppressors) are switched off, or genes that encourage cell division (oncogenes) are overactive.

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Meiosis has various timescales in different organisms, which can be affected by several factors including temperature and environment of the organism, and the amount of nuclear DNA. The process lasts 6 hours in yeast but can last more than 40 years in human females, due to a developmental hold at prophase I, until ovulation. Other examples are 1-2 days in male fruit flies and ~ 24 days in human males. [1]

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Mitosis is usually shorter than meiosis. The process can take over 10 hours for mammalian cells in culture [2], budding yeast can take ~80 minutes to complete a cell cycle [3], whilst bacteria can divide every 20 minutes.

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Only organisms which perform sexual reproduction. Archaea and bacteria do not do this, so it might be tempting to think that unicellular organisms do not sexually reproduce. However, there are exceptions; budding yeast will form haploid spores under nutritional deprivation.

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Mitosis is performed by unicellular and multicellular eukaryotes. Bacteria have their own version of mitosis called “binary fission”. This is distinct from meiosis as bacteria typically have one circular chromosome, which is not contained within a nucleus, like eukaryotic chromosomes.

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8 stages in total (plus interphase)

Happens in germ cells

Purpose is sexual reproduction

Produces 4 haploid daughter cells

Chromosome number is halved in each daughter cell

Genetic variation increased

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4 stages in total (plus interphase)

It happens in the somatic cells

The purpose is cellular proliferation

Produces 2 diploid daughter cells

The chromosome number remains the same

Genetic variation does not change

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Four haploid cells with different genetic information.

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Two diploid cells with identical genetic information.

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To create gametes with only one copy of the organism’s genetic information, in preparation for sexual reproduction. Various steps in meiosis create opportunity for genetic diversity in the daughter cells. This is the raw substrate for evolution.

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In a unicellular organism, the purpose of mitosis is to proliferate as a species. In a multicellular organism, the purpose can be to grow during development, or to repair or regenerate
a damaged tissue, for example.

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Mitosis is the process by which body cells divide and create copies of themselves for growth and repair.

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Mitosis is the process by which body cells divide and create copies of themselves for growth and repair.

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(Technology Networks, 2022)

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In meiosis, the new cells have half the genetic material of the parent cell and is the process by which egg and sperm cells are formed.

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In meiosis, the new cells have half the genetic material of the parent cell and is the process by which egg and sperm cells are formed.