Biology Reference
In-Depth Information
γ
G
Fetal
γ
A
Embryonic
ε
β
Adult
δ
Hemoglobins
α1
Adult
α2
Embryonic
ζ
Myoglobin
-800
-500 -400
Time(million years before present)
-200
-100 -40
Fig. 4.
Oxygen-transporting globins. Successive gene duplications have created a
diverse gene family. Each gene in the family fulfills a different function. Hemoglobins
transport oxygen in the blood, with various specializations, while myoglobin trans-
ports oxygen in muscles.
800 million years in the past, another gene duplication event created the
separate lineages of myoglobin and hemoglobins.
Both the pig and the human genomes contain genes for various
hemoglobins. Given a data set consisting of all the available
α
-hemoglo-
bin sequences from tetrapods, in which human
β
-hemoglobin rather
than human
-hemoglobin would inadvertently have been included, an
erroneous phyletic tree would be produced in which the human species
would be shown to have diverged from many other tetrapods 500 million
years ago, instead of a few tens of millions of years ago from a smaller num-
ber of tetrapods, all mammalian (this is readily seen by following in Fig. 5
the path from human
α
β
-hemoglobin to the first internal node, then to
-hemoglobin). Hence, another pitfall in phylogenetic reconstruction.
Such a result would evidently appear as wrong to the knowledgeable,
leading the data to be viewed with suspicion. However, not all cases of
incorrect trees produced through an inappropriate mixture of orthologs
pig
α
