Can we write instructions with only 4 (or 5) letters?
The answer to that is “yes”! Our cells’ genetic instructions are written using only the letters A, C, T or U and G. Can you believe that?
If that is the case, how come there are so many different cells? How come we are different from each other?
Well, these letters vary in number as well as in their sequence in every cell. Also, sometimes not all the sequences of these letters are active at the same time. If for example we designate numbers to the various sequence of these letters in a cell, it’s possible that only sequences 1, 2, and 3 are active in one cell while it can be sequences 1, 5, and 8 in another cell.
So if you think about it, just varying the number of A, T, C and G as well as their sequence in a cell are enough to produce almost limitless variety of combinations.
By the way, in the genetic alphabet, A always pairs with T or U and C always pairs with G. So that actually limits the combinations because there will always be the same number of A and T or U and equal number of C and G. Still even with this constraint, the possibilities are almost limitless.