The cell-free in vitro translation system utilized by Nirenberg and Matthaei to determine the first "words" in the genetic code utilized addition of into purified E. coli extracts:

Radio active amino acids

Explanation:

The Nirenberg and Matthaei performed the experiment which showed the relationship between the nitrogenous bases present on the mRNA and the amino acids.

They knew that the amino acids are coded by the bases on the mRNA and they cultured the E.coli bacteria, ruptured them and released the cytoplasmic content from them.

Then they added the artificially synthesized RNA molecule attached with radioactive molecules and added them to different tubes. From this, they concluded that there is 64 combination of triplets which are responsible for the production of a variety of amino acids.

Thus, Radioactive amino acids are the correct answer.

i'm gonna put a couple so you can chose from

explanation:

if you know the fur color of the offspring mice, you can use the ratios to identify the genotypes of the parents.

if either parent mouse passes a dominant allele, the offspring will have black fur.

if the parental mice has two different fur color (i.e white and black) , the color of the offspring's fur would be either black, white, or the combination of both (grey)

hope this : )

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.