didi1011
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Table 2 contains selected taxa for five species of chordates, and differences in the amino acid sequences of the beta polypeptide of haemoglobin, compared with the human form. (Note that the Eutheria is the sub-class of placental mammals, whereas the Metatheria is the sub-class of pouched mammals, the marsupials.)
Table 2 Selected taxa for five species and features of their beta polypeptides
Species Taxa Amino acid differences of the beta polypeptide cf the human beta polypeptide Class Sub-class Order Human Mammalia Eutheria Primates 0 Dog Mammalia Eutheria Carnivora 15 Frog Amphibia X X 67 Gorilla Mammalia Eutheria Primates 1 Grey kangaroo Mammalia Metatheria X 38
The beta polypeptide of human haemoglobin has 146 amino acids, in the same sequence in most humans. The beta polypeptide of dog haemoglobin has 15 amino acid differences from the predominant human form. a) Using evolutionary theory, explain why 90% of the amino acid sequence of the beta polypeptide of human haemoglobin occurs in the beta polypeptide of dog haemoglobin?
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TSR Jessica
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h3rmit
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(Original post by didi1011)
The beta polypeptide of human haemoglobin has 146 amino acids, in the same sequence in most humans. The beta polypeptide of dog haemoglobin has 15 amino acid differences from the predominant human form. a) Using evolutionary theory, explain why 90% of the amino acid sequence of the beta polypeptide of human haemoglobin occurs in the beta polypeptide of dog haemoglobin?
As the human-dog common ancestor existed reasonably long ago, and we have diverged since then, there has been lots of time for our genomes to change by mutations, recombination, transposon inputs, etc, as well as different selection pressures that select for specific phenotypes with specific proteins. As our DNA has changed, and DNA codes for the amino acids like haemoglobin, some of our proteins will be different as they have different amino acid sequences.

90% similarity is quite high though, and that will probably be because haemoglobin is an essential protein for O2 and CO2 transport, and hence any changes to any it could be disastrous and extremely detrimental to the organism, resulting in a strong selection pressure against the "bad" haemoglobin. Therefore, proteins fundamental to the function of all cells like haemoglobin will be more conserved then other, more specific and less essential proteins.
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