Human adult hemoglobin is a tetramer containing two alpha...

Human adult hemoglobin is a tetramer containing two alpha (a) and two beta ( $\beta$ ) polypeptide chains. The $\alpha$ gene cluster on chromosome 16 and the $\beta$ gene cluster on chromosome 11 share amino acid similarities such that 61 of the amino acids of the $\alpha$ -globin polypeptide ( 141 amino acids long) are shared in identical sequence with the $\beta$ -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? Include in your answer a link to Ohno's hypothesis regarding the origin of new genes during evolution.

Human adult hemoglobin is a tetramer containing two alpha
(a) and two beta ( $\beta$ ) polypeptide chains. The $\alpha$ gene cluster on chromosome 16 and the $\beta$ gene cluster on chromosome 11 share
amino acid similarities such that 61 of the amino acids of the
$\alpha$ -globin polypeptide ( 141 amino acids long) are shared in identical sequence with the $\beta$ -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? Include in your answer a link to Ohno's hypothesis regarding the origin of new genes during evolution.

Key Concepts

Gene Duplication

Gene duplication is a fundamental evolutionary process where an organism gains an extra copy of a gene, which provides a redundant set that can accumulate mutations without detrimental effects on the original gene's function. This process is a key mechanism for generating genetic diversity and allows one copy to maintain the original function while the other is free to develop new or specialized functions over time.

Divergence of Duplicated Genes

Once a gene is duplicated, the extra copy can diverge through mutations over evolutionary time. This divergence can lead to differences in the protein products, such as variations in amino acid sequences, while still retaining core structural or functional elements. This process explains how gene products with shared sequences can end up performing related but not identical roles, as seen in the alpha and beta globin chains.

Paralogous Genes

Paralogous genes are genes within the same organism that arose from duplication events and subsequently diverged in function. The alpha and beta globin genes are an example of paralogs; although they share a common ancestry and certain amino acid sequences, they are located on different chromosomes and have evolved distinctive features that contribute to the structure and function of hemoglobin.

Ohno's Hypothesis

Ohno's hypothesis posits that gene duplication is a primary source of new genes and evolutionary innovation. It suggests that duplicated genes can acquire novel functions or subfunctionalize, providing an important mechanism for the evolution of complexity in organisms. The divergence of the alpha and beta globin genes exemplifies this concept, as they originated from a common ancestral gene and have evolved in parallel to support the unique properties of human hemoglobin.

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