AP BIOLOGY

Detailed explanation-1: -Because the DNA sequence determines a protein’s amino acid sequence, a gene shared by two closely related organisms should have similar, or even identical, amino acid sequences. That’s because closely related species most likely diverged from one another fairly recently in the evolutionary span.

Detailed explanation-2: -Biologists have perfected techniques for determining the sequence of amino acids in proteins. By comparing the amino acid sequences in homologous proteins of similar organisms and of diverse organisms, evolutionary relationships that might otherwise go undetected can be determined.

Detailed explanation-3: -As protein-coding DNA sequences evolve as triplets of nucleotides (codons) and it is known that sequence similarity degrades more rapidly at the DNA than at the amino acid level, alignments are generally more accurate when based on amino acids than on their corresponding nucleotides.

Detailed explanation-4: -Amino acid data can yield the same descent tree, or relatedness matrix as the DNA data. The information is cruder, and sometimes even missing because not all DNA mutations cause a different amino acid sequence. Some DNA mutations are silent, the new codon codes exactly the same amino acid as the old.

Detailed explanation-5: -Similar anatomy found in different species may be homologous (shared due to ancestry) or analogous (shared due to similar selective pressures). Molecular similarities provide evidence for the shared ancestry of life. DNA sequence comparisons can show how different species are related.