Shown below are two homologous lengths of the alpha and beta chains of human hemoglobin. Consult a genetic code dictionary (Figure 13.7), and determine how many amino acid substitutions may have occurred as a result of a single nucleotide substitution. For any that cannot occur as a result of a single change, determine the minimal mutational distance.

Alpha: ala val ala his val asp asp met pro
Beta: gly leu ala his leu asp asn leu lys

Key Concepts

Homologous Sequences

Homologous sequences are DNA, RNA, or protein sequences that share a common ancestry. In the context of the question, the alpha and beta chains of hemoglobin are homologous proteins, meaning they evolved from a common ancestral gene. Analyzing these sequences helps identify similarities and differences that may arise from mutations, such as single nucleotide substitutions.

Amino Acid Substitution

Amino acid substitution occurs when a single nucleotide change in the DNA sequence leads to the replacement of one amino acid with another in the protein sequence. This can affect the protein's structure and function. Understanding how these substitutions arise from nucleotide changes is crucial for determining the potential impact of mutations on protein function.

Mutational Distance

Mutational distance refers to the number of changes required to transform one sequence into another. In this context, it involves calculating how many nucleotide changes are necessary to convert the alpha chain sequence into the beta chain sequence. This concept is essential for understanding the genetic variations and evolutionary relationships between homologous proteins.