This is a comprehensive and detailed note that contains unit 2 topics;4.1 Evolution and Classification; 4.2 Determining Phylogenetic Connections; 5.1 Prokaryotic Cell Structures.
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4.1 Evolution and Classification
Intro
● All living organisms are on earth are related.
● Phylogeny- The evolutionary history and relationship of an organism or group
of organisms.
○ It describes the relationships of an organism, which organisms from
which it is thought to have evolved, to which species it is most closely
related, and so forth.
○ Phylogenetic relationships provide info on shared ancestry but not
necessarily on how organisms are similar or different.
Phylogenetic Trees
● Phylogenetic tree- a diagram used to reflect evolutionary relationships
among organisms or groups of organisms.
○ They are considered to be hypotheses of the evolutionary past
○ “Tree of life” can be constructed to illustrate when different
organisms evolved and to show the relationships among different
organisms.
○ Can be read like a map of evolutionary history
○ Many have a single lineage at the base representing a common
○ Rooted phylogenic trees- there is a single ancestral lineage (typically
drawn from bottom or left) to which all organisms represented in the
diagram are related.
○ Unrooted trees- don’t show a common ancestor but do show
, relationships among species.
○ Branch point- the point where a split occurs.
■ Represents where a single lineage evolved into a distinctly new
one.
○ Basal taxon- A lineage that evolved early from the root and remains
unbranched
○ Sister taxa- when two lineages stem from the same branch point
○ Polytomy- a branch with more than two lineages
● Phylogenic trees can serve as a pathway to understanding evolutionary
history.
○ The pathway can be traced from the origin of like to any individual
species.
○ By starting with a single species and tracing backward, one can
discover the species’ ancestors and where lineages share a common
ancestry.
○ The trees can be used to study entire groups of organisms.
● Rotation at branch points does not change the information
● Many disciplines within the study of biology contribute to understanding how
past and present life evolved over time.
, ● Information is used to organize and classify organisms based on evolutionary
relationships in a scientific field called systematics.
● Since phylogenetic trees are hypotheses, they will continue to change as new
types of life are discovered and new information is learned.
Limitations of Phylogenetic Trees
● It can be assumed that closely related organisms look alike, and while this is
often the case, it is not always true.
● If two closely related lineages evolved under significantly different
conditions or after the evolution of a major adaptation, it is possible for the
two groups to appear more different than other groups that are not as
closely related.
○ Ex: the phylogenetic tree to the right shows that lizards and rabbits
both have amniotic eggs, whereas frogs do not, yet lizards and frogs
visually appear more similar than lizards and rabbits.
● Unless otherwise indicated, the branches do not account for the length of
time, only the evolutionary order.
○ It shows the order in which things took place.
● Any phylogenetic tree is a part of the greater whole, and like a real tree, it
does not grow in only one direction after a branch develops.
○ So that does not mean that in the diagram above, just because a
vertebral column evolved does not mean that invertebrate evolution
ceased, it only means that a new branch formed.
● Groups that are not closely related, but evolve under similar conditions, may
appear more phenotypically similar to each other than to a close relative.
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