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  • Sex Verification Testing of Athletes

    Sex Verification Testing of Athletes

    Click & Learn

    This interactive explores the biology of sex determination and development in humans, set against the backdrop of the different sex testing policies implemented throughout sports history.

  • Identifying the Key Genes for Regeneration

    Identifying the Key Genes for Regeneration

    Scientists at Work

    (9 min 55 sec) Planarians have an amazing ability to regenerate lost tissues. In this video, scientists knock out two different genes in planaria to start to understand how the process works—and they generate animals with two heads and two tails!

  • Development of the Cerebral Cortex

    Development of the Cerebral Cortex

    Animation

    (1 min 43 sec) Most of the neurons of the cerebral cortex arise from progenitor cells that undergo repeated cell division.

  • Development of the human embryonic brain

    Development of the human embryonic brain

    Animation

    (1 min 40 sec) The fetal brain grows enormously during pregnancy, both in terms of its size and the number of neurons it has.

  • Signal molecules trigger transcription factors

    Signal molecules trigger transcription factors

    Animation

    (2 min 4 sec) Varying concentrations of a signaling molecule activate different transcription factors and determine cell fate.

  • Planarian Regeneration and Stem Cells

    Planarian Regeneration and Stem Cells

    Scientists at Work

    (11 min 47 sec) A mini-documentary discussing the remarkable regenerative capabilities of the planarian, and how HHMI researcher Alejandro Sánchez Alvarado uses them to study the biology of stem cells.

  • X Inactivation

    X Inactivation

    Animation

    (55 sec) This animation shows how the random deactivation of one of the X chromosomes in a pair can lead to a mozaicism in the expression genes.