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). Part A How might one explain the existence of two polypeptides with partially shared function and structure on two different chromosomes

The similarity between the amino acid sequences between the two polypeptide chains indicates that some time ago there was the existence of only one sequence, however, later on, the phenomenon of duplication took place. Due to duplication, the emergence of two similar sequences took place adjacent to each other in one chromosome.  

Post duplication it was due to chromosomal aberration that the two sequences got positioned on distinct chromosomes. This resulted in the positioning of the alpha polypeptide chain on chromosome 16, and on chromosome 11 beta polypeptide chain got positioned.  

However, due to mutations, the two polypeptide chains do not exhibit complete similarity. Post duplication to the current time both the sequences would have gone through various mutations resulting in the reduction of the entire similarity of the genes.