Why did geneticists believe, even before direct experimental evidence was obtained, that the genetic code would turn out to be composed of triplet sequences and be nonoverlapping? Experimentally, how were these suppositions shown to be correct?

The genetic code is a set of rules that defines how the sequence of nucleotides in DNA is translated into the amino acid sequence of proteins. It is composed of codons, which are triplet sequences of nucleotides. Each codon corresponds to a specific amino acid or a stop signal during protein synthesis, making the code essential for understanding how genetic information is expressed.

Triplet codons are sequences of three nucleotides that encode a single amino acid in the process of translation. Geneticists hypothesized that the code was triplet-based because there are 20 standard amino acids, and using combinations of three nucleotides (4^3 = 64 possible combinations) provides sufficient diversity to encode all amino acids and stop signals. This triplet nature was crucial for the nonoverlapping characteristic of the genetic code.

Experimental validation of the genetic code's triplet and nonoverlapping nature was achieved through various methods, including the use of synthetic RNA and ribosomes. By introducing specific RNA sequences and observing the resulting protein synthesis, researchers demonstrated that the reading frame of the RNA was maintained without overlap, confirming that each codon was read independently and sequentially, thus supporting the initial hypotheses.