Two designs so far are DNA and RNA versions of the genetic code. A third is the label from my GM Tomato beer -- the bottle 'collar' can be put on the back of the shirt near the neck or on one of the sleeves. Other designs featuring DNA replication will follow shortly.
You can download the designs as PDF files, then print them out using any colour dot-matrix printer onto special T-shirt transfer paper. This is readily-obtainable from stationers such as W.H. Smith in the UK, or on-line from numerous suppliers.
Please follow the manufacturer's instructions carefully when printing from this special paper onto fabric (and subsequently, for washing and ironing the shirt).
These first designs are suitable only for printing on light-coloured or white T-shirts, as the 'white' parts are not printed using white ink, of course. All three designs have been reversed so that they appear the right way round when transferred to fabric.