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  • The Beak of the Fish

    The Beak of the Fish

    Image of the Week

    The teeth of adult pufferfish are fused to form a beak used for crunching into hard prey such as shellfish.

  • Larval Biscuit

    Larval Biscuit

    Image of the Week

    A pluteus larva of the sea biscuit, Clypeaster subdepressus, an echinoderm closely related to sea urchins.

  • One Bone, Two Bones...

    One Bone, Two Bones...

    Image of the Week

    This short-tailed fruit bat embryo shows a pattern of bones in its limbs characteristic of all tetrapods: one bone, two bones, lots of bones, digits. 

  • Classroom Activities: Gene Switches

    Classroom Activities: Gene Switches


    To accompany the lecture series Evolution: Constant Change and Common Threads.

  • Pitx1 Expression

    Pitx1 Expression


    (55 sec) In the stickleback fish, pelvic-fin reduction resulted from changes in the regulatory switch elements of the Pitx1 gene. In the marine ancestor, the Pitx1 gene is activated in the pelvic-fin region during development to generate the fin. In the pelvic-reduced stickleback, the regulatory switch that normally turns on the Pitx1 gene is either missing or non-functional.