Question

which statement explains why the gene of a frog may be inserted into a bacterial chromosome?
c. one dna allele produces one enzyme in all organisms.
a. nucleotides are the basic units of dna for all organisms.
b. dna forms purines and pyrimidines in all organisms.
d. dna has equal amounts of adenine and thymine for all organisms.

Explanation:

To determine why a frog gene can be inserted into a bacterial chromosome, we analyze the options:

• Option C: The "one gene - one enzyme" hypothesis is not the key reason for cross - species gene insertion. It focuses on the relationship between genes and enzymes, not on the compatibility of DNA for insertion.
• Option A: All organisms (including frogs and bacteria) have DNA composed of nucleotides as the basic unit. This means that the chemical structure of DNA is fundamentally the same across different species. So, a frog's DNA (made of nucleotides) can be recognized and integrated into a bacterial chromosome (also made of nucleotides) because the basic building blocks are identical.
• Option B: The fact that DNA forms purines and pyrimidines in all organisms is not the main reason for gene insertion. The presence of these bases does not directly relate to the ability to insert a foreign gene.
• Option D: The equal amounts of adenine and thymine in DNA (Chargaff's rule) is about the base - pairing ratio within a DNA molecule, not about the compatibility for gene insertion between different species.

So, the correct option is A as it explains the chemical compatibility of DNA across species, allowing a frog gene (DNA) to be inserted into a bacterial chromosome.

Answer:

A. Nucleotides are the basic units of DNA for all organisms.