Question

Previously we discussed the importance of humans having multiple hemoglobin genes (alpha, beta, epsilon, gamma, and zeta). However, not all animals have this many hemoglobin genes. We estimate that the first ancestral hemoglobin gene formed about 800 million years ago. At that time there was only this one hemoglobin gene.

A) From what you've learned about chromosomal modifications/alterations what event must have occurred to form the hemoglobin gene family we see in humans (i.e. going from 1 ancestral hemoglobin to at least five specialized hemoglobin genes).

B) Would the formation of these other hemoglobin genes have occurred all at once or would it have occurred gradually over many millions of years? Make an educated guess...you won't lose points if you are wrong.

Answer 1

The globin genes have evolved by duplication, variation, translocation and further duplications.

In the begining there was a single globin gene that can be called either as α or β globin gene. The first event in the evolution of the globin gene is a duplication that resulted in the production of a second copy of the globin gene in the genome. Now these copies diverged into α and β globins by the accumulation of point mutations. Later α and β globins separated by a translocation event into two separate chromosomes. The α and β globins now present on two different chromosomes further duplicated and diverged. The alpha diverged into alpha and zeta genes and beta diverged into epsilon, gamma, delta and beta genes.

All present day globin genes have evolved from an ancestral globin gene. In the various evolutionary phylas only birds and mammals have separate clusters for α and β globins. The human β-globin locus is located on a short region of chromosome 11 and α on chromosome 16. The α and β genes must have been physically separated before the birds and mammals diverged from their common ancestor. The separation of birds and mammals from a common ancestor occurred about 270 million years ago. The preceding stage of the globin gene is represented by the globin genes in the frog X. laevis, where α and β globin genes are linked lying only about 8kb apart. The amphibians separated from the mammalian and avian line of evolution about 350 million years ago. So the separation of α and β globin genes might have occurred probably by a transposition event somewhere around the period of early vertebrate evolution. Some primitive fishes (e.g. lamprey) have only a single type of globin chain, which can be called either as α or β globin. The fishes might have diverged from the mammalian, avian and amphibian line of evolution before the ancestral globin gene was duplicated to give rise to the α and β variants, approximately 500 million years ago during the evolution of bony fish. The history of evolution can be traced further back.