Suppose that you discover a new life form on Mars. These organisms have DNA containing the same four nucleotides as Earth DNA. They also make proteins using a triplet code, so they use the same 64 codons that Earth organisms do. Martian proteins are also similar to Earth proteins, but it turns out that Martian proteins use 24 different amino acids instead of just 20.
How might you expect the Martian code to differ from the Earth code? To put it another way, if Earth life forms actually originated on Mars, what changes in the Martian code could have resulted in the Earth code? To put it still another way, what changes in the Earth code would be necessary to accommodate 4 additional amino acids?
Justify the changes you select. What other genetic changes would be necessary to support the assignment of new codons?