Amino acids are required for the synthesis of proteins. Living cells typically have biosynthetic pathways to synthesize at least some of the amino acids used in making proteins. Some strains of E. coli, a prokaryote, can synthesize the amino acid tryptophan, while other E. coli strains cannot. Similarly, some strains of the yeast S. cerevisiae, a eukaryote, can synthesize tryptophan, while other S. cerevisiae strains cannot. Similarly, some strains of the yeast S. cerevisiae, a eukaryote, can synthesize trypotphan, while other strains cannot.
Which of the following describes the most likely source of genetic variation found in the trytophan synthesis pathways of both species?
a. Exchange of genetic information occurs through crossing over
b. Viral transmission of genetic information required to synthesize tryptophan occurs
c. Random assortment of chromosomes leads to genetic variation
d. Errors in DNA replication lead to genetic variation

Sequencing a large number of prokaryotic genomes from an assortment of phyla and classes has offered new chances to contemplate prokaryotic evolution. There are a few techniques to contemplate the atomic evolution of genomes through quality exchanges. The ordinarily utilized one is through looking for grouping closeness utilizing phylogenetic models, however various different methodologies incorporate recognizable proof of codon use designs, base organization (GC content) investigation, and nucleotide-design properties inside genomes that vary from the genomic standard, as these are probably going to speak to obtained successions.
Pathway evolution has been contemplated from the "starting point of life" setting, and two speculations have been advanced to clarify the advancement of the arrangement of steps in a pathway. Right now, endeavor to contemplate pathway evolution from an alternate point of view. Intracellular biosynthetic pathways comprise different response steps catalyzed by proteins, whose qualities for the most part structure a gathering (operon) in microorganisms.
Hence, the right answer is option b" Viral transmission of genetic information required to synthesize tryptophan occurs.