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2.12: Twins

  • Page ID
    204950
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    Monozygotic or identical twins occur when a fertilized egg splits apart in the first two weeks of development. The result is the creation of two separate, but genetically identical offspring. That is, they possess the same genotype and often the same phenotype. About one-third of twins are monozygotic twins.

    Early childhood identical twins with long hair smiling at the camera
    Figure \(\PageIndex{1}\): Monozygotic Twins[2] Figure – MZ twins look very alike – indeed “identical”

    Dizygotic/Fraternal

    Sometimes, however, two eggs or ova are released and fertilized by two separate sperm. The result is dizygotic or fraternal twins. These two individuals share the same amount of genetic material as would any two children from the same mother and father. In other words, they possess a different genotype and phenotype. They are no more similar or different than any other biological pair of siblings - the only difference being that they are the same age.

    Fraternal twinning often runs in families. It would appear that it is a genetic trait that tends to occur commonly in some families. So you might see that some families like mine don't have any twins, while other families like my daughter-in-law's have many twin pairs born.

    DZ twins -one with long hair and dressed in pink, and other with short hair and dressed in a blue shirt and cargo shorts
    Figure \(\PageIndex{1}\): Dizygotic Twins[3] Figure – DZ twins are no more similar than any other siblings born at the same time

    sequence of fraternal and identical twin conception

    Attributions:

    Child Growth and Development by Jennifer Paris, Antoinette Ricardo, and Dawn Rymond, 2019, is licensed under CC BY 4.0

    [1] Lifespan Development: A Psychological Perspective (page 36) by Martha Lally and Suzanne Valentine-French is licensed under CC BY-NC-SA 3.0

    [2] Image is in the public domain

    [3] Image by Jennifer Paris used with permission

    Fraternal twins [Image] by National Human Genome Research Institute in the public domain


    2.12: Twins is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.

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