Question

question 1-9
which statement best explains how the genetic code is universal?
dna sequences are unique for each species.
the shape of a dna molecule is the same in different species.
a dna sequence codes for the same proteins in different species.
the nucleotide ratios in the dna molecule are different between species.

Explanation:

To determine which statement explains the universal genetic code, we analyze each option:

• Option 1: "DNA sequences are unique for each species" explains species - specific DNA, not universality.
• Option 2: "The shape of a DNA molecule is the same in different species" (DNA is double - helix in most, but this doesn't relate to the genetic code's universality).
• Option 3: "A DNA sequence codes for the same proteins in different species" - The genetic code is universal because the same DNA codons (sequences) code for the same amino acids (and thus same proteins) across different organisms. For example, the codon AUG codes for methionine in bacteria, plants, and animals.
• Option 4: "The nucleotide ratios in the DNA molecule are different between species" - This is about nucleotide proportions, not the genetic code's universality.

Answer:

C. A DNA sequence codes for the same proteins in different species.