16 SEP 2011 by ideonexus
Hen's Teeth
Some atavisms can be produced in the laboratory. The most amazing
of these is that paragon of rarity, hen’s teeth. In 1980, E. J. Kollar and
C. Fisher at the University of Connecticut combined the tissues of two
species, grafting the tissue lining the mouth of a chicken embryo on top
of tissue from the jaw of a developing mouse. Amazingly, the chicken
tissue eventually produced tooth-like structures, some with distinct roots
and crowns! Since the underlying mouse tissue alone could not prod... 1 
notes
notesAn experiment from 1980 that stimulated hens to grow teeth by triggering a gene holdover from their ancient reptilian ancestors.
16 SEP 2011 by ideonexus
Atavism In Modern Horses
Modern horses, which descend from smaller, five-toed ancestors,
show similar atavisms. The fossil record documents the gradual loss
of toes over time, so that in modern horses only the middle one—the
hoof—remains. It turns out that horse embryos begin development with
three toes, which grow at equal rates. Later, however, the middle toe
begins to grow faster than the other two, which at birth are left as thin
“splint bones” along either side of the leg. (Splint bones are true vestigia... 1 notes
notesModern horses have a common birth defect of growing extra toes from when their ancestors had them.
