Human adult hemoglobin is a tetramer containing two alpha (α) and two beta (β) polypeptide chains. The α gene cluster on chromosome 16 and the β gene cluster on chromosome 11 share amino acid similarities such that 61 of the amino acids of the α-globin polypeptide (141 amino acids long) are shared in identical sequence with the β-globin polypeptide (146 amino acids long). How might one explain the existence of two polypeptides with partially shared function and structure on two different chromosomes?

Verified step by step guidance

1. Understand that the α and β globin genes are part of a gene family, which are groups of related genes that have similar sequences and often similar functions.
2. Recognize that gene families often arise through the process of gene duplication, where an ancestral gene is copied, and the copies can evolve independently over time.
3. Consider that after duplication, one copy of the gene might accumulate mutations that allow it to take on a new function, while the other copy retains the original function, leading to functional divergence.
4. Acknowledge that the shared amino acid sequences between α and β globin suggest that they have conserved regions important for their function, likely due to evolutionary pressures to maintain these sequences.
5. Realize that the presence of these genes on different chromosomes could be a result of chromosomal rearrangements over evolutionary time, which can separate duplicated genes onto different chromosomes.

Key Concepts

Gene Duplication

Gene duplication is a process where a segment of DNA is copied, resulting in two identical or similar genes. This can lead to the evolution of new functions as one gene may retain the original function while the other accumulates mutations over time. In the case of hemoglobin, the α and β globin genes likely arose from a common ancestral gene through duplication, allowing for specialization in function while maintaining some structural similarities.

Chromosomal Location and Evolution

The location of genes on different chromosomes can influence their evolutionary paths. Genes that are located on separate chromosomes, like the α and β globin genes, can evolve independently, allowing for variations in expression and function. This separation can lead to the development of distinct polypeptides that still share functional roles, as seen in the cooperative binding of oxygen by hemoglobin.

Functional Redundancy

Functional redundancy refers to the phenomenon where different genes or proteins can perform similar functions within a biological system. In the case of hemoglobin, the α and β chains exhibit functional redundancy in oxygen transport, allowing for a robust system that can adapt to varying physiological conditions. This redundancy can be advantageous, as it provides a backup mechanism if one polypeptide is mutated or not expressed.