ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Genetics - Meiosis

Updated on February 9, 2014


Before reading the rest of this hub you should probably familiarise yourself with the following definitions as they will crop up quite a lot!

  • Haploid - a single set of unpaired chromosomes in the nucleus of a cell (23 chromosomes).
  • Diploid - a full set of chromosomes within the nucleus of a cell (46 chromosomes).
  • Locus (loci) - the position of a gene on a chromosome.
  • Maternal chromosomes - the chromosomes that were contributed by the egg.
  • Paternal chromosomes - the chromosomes that were contributed by the sperm.
  • Crossing over - when lengths of DNA 'cross over' from one chromatid to another.
  • Chromatid - one copy of a duplicated chromosome which is joined to the other copy by a centromere.
  • Allele - an alternative form of a gene that has a difference in the DNA base pairs and thus is translated into a slightly different polypeptide. The alleles are found at the same place on a chromosome.
  • Chromatin - the material of which the chromosomes in eukaryotic organisms are composed (i.e. a combination of DNA and proteins).
  • Bivalent - a pair of homologous chromosomes.

What is Meiosis?

Meiosis is a type of nuclear division necessary for sexual reproduction in eukaryotes, such as animals, plants and fungi. The process of meiosis happens in two separate divisions called meiosis I and meiosis II and each division has four stages. The end result of meiosis is four haploid cells.

Crossing over

At the chiasmata the chromosomes may break and the broken ends will rejoin to the other chromatid in the bivalent and results in similar sections of the chromatids being swapped over. The sections that are swapped contain the same genes but often have different alleles.

Meiosis I - Prophase I

At this stage the chromosomes have already been duplicated. It is during prophase I that the chromatin start to condense and undergo 'supercoiling' and as a result become shorter and thicker. At this point they can take up stain and can be seen under a light microscope. The chromosomes then come together and form a bivalent consisting of one maternal and one paternal chromosome. The chromosomes then wrap around each other and will attach at points called chiasmata which are the site that undergo the process of crossing over. The nucleolus then disappears and the nuclear envelope disintergrates. In the cytoplasm, a spindle, consisting of microtubules and other proteins, forms between the two pairs of centrioles and the centrioles will then migrate to opposite poles of the cell.

Metaphase I

The bivalents then line up across the equator, still attached to the spindle microtubules. The maternal and the paternal chromosomes in the bivalent are facing opposite poles of the cell which allows them to be pulled apart correctly during the next process.

Anaphase I

During this stage the maternal and paternal homologous chomosomes in each bivalent are pulled apart by the spindle microtubules to each pole of the cell. A key thing to remember about this process is the despite the fact the bivalents are separating the sister chromatids remain attached to one and other by the centromere.

Telophase I

The two homologous chromosomes have finished their migration to each pole of the cell. Two nuclear envelopes then form - one around each chromosome set. The cell then divides by a process called cytokinesis which involves the formation of a cleavage furrow which results in the 'pinching' of the cell into two cells. There is a brief interphase where the chromosomes uncoil.

Meiosis II - Prophase II

The following stages are much the same as the ones in meiosis I however the division takes place on a plane that is at right angles to the original divisions. In prophase I the reformed nuclear envelope breaks down and disintegrates and the nucleolus disappears. The chromosomes then once again condense and spindles form.

Metaphase II

Single chromosomes align themselves down the centre (equator) of the spindle and each of the chromatids is randomly arranged.

Anaphase II

The centromeres divide and the chromatids are pulled to the opposite end of the cells (poles) by the spindle fibres and the chromatids randomly segregate.

Telophase II

A nuclear envelope forms around each of the haploid daughter cells and cytokinesis takes place. This produces four gametes each with a haploid set of chromosomes.

Genetic Variation and Meiosis

There are many ways that meiosis and fertilisation can lead to genetic variation within a population. Crossing over (described above) is important because it means that every daughter chromosome is different from the parent ones and carries a new combination of alleles. This means that when the gametes join at fertilisation the resulting zygote is genetically different from the parent.

Genetic reassortment which is the consequence of the random distribution of maternal and paternal chromosomes on the equator in metaphase I and thee segregation of these bivalents into two daughter nuclei in anaphase I. The reassortment of chromatids also leads to genetic variation. In metaphase II the chromatids randomly distribute along the spindle equator and how they align determines how they will segregate in anaphase II.


    0 of 8192 characters used
    Post Comment
    • profile image


      4 years ago

      Mitosis is formation of same copy of genetic material and in mitosis the combination of genetic material varies.

      Am i right?


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)