What do they look like?

Specimen jar containing three female Japanese Bitterlings
© The Board of Trustees of the Science Museum

Two genetically engineered pig kidneys, 1999
© The Board of Trustees of the Science Museum

Genetically engineered mouse brain, 2010
© The Board of Trustees of the Science Museum

Pig heart in liquid paraffin, 1960
© The Board of Trustees of the Science Museum