4.6.9 Genetic Relationships Between Organisms

Ways to Assess Genetic Relationships

1. DNA Base Sequences:

• Comparing the base sequence of DNA between organisms reveals how closely related they are.
• A higher percentage of similarities in DNA sequences indicates a closer evolutionary relationship.

2. mRNA Base Sequences:

• mRNA is complementary to DNA, so comparing mRNA sequences gives a similar level of insight into genetic relationships.

3. Amino Acid Sequences in Proteins:

• The sequence of amino acids in proteins, such as cytochrome C or haemoglobin, can be compared.
• A smaller number of differences in amino acid sequences indicates closer relationships.

4. Immunological Comparisons:

• Proteins from one species can be tested with antibodies from another species.
• A greater degree of antibody-protein reaction (e.g., formation of precipitates) indicates closer genetic similarity.

Key Concepts

• Homologous Genes: Genes inherited from a common ancestor, which may retain similar functions across species.
• Molecular Phylogeny: The analysis of molecular data (DNA, RNA, proteins) to determine the evolutionary relationships between species.

Exam Application

• Use data such as DNA base sequences, amino acid sequences, or immunological reactions to evaluate genetic relationships.
• Discuss the importance of comparing multiple genetic markers to ensure accuracy.
• Understand that greater genetic similarity reflects closer common ancestry.