BIOLOGY 1M03 Lecture Notes - Lecture 4: Phylogenetic Tree, Ribosomal Rna, Design Of ExperimentsPremium
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BIOLOGY 1M03 - Lecture 4 - The Tree of Life (Continued)
Using Molecules to Understand the Tree of Life:
● Carl Woese and colleagues studied a small subunit known as rRNA, as a means
for understanding the evolutionary relationships among organisms.
○ For example, SSU rRNA (small subunit rRNA) is a nucleic acid that
constitutes partially ribosomes (the protein producing organelles in cells).
○ They discovered that rRNA sequences should be very similar in closely
related organisms, but less similar in organisms that are less closely
related; species in the same evolutionary lineage should share particular
changes in rRNA.
■ It can be concluded that a phylogenetic tree is a diagram that may
be interpreted as depicting these relationships among species.
Taxa (plural for taxon, a group of any rank, such as a species,
family, or class) that may be inferred to have shared an immediate
common ancestor are closely related; other taxa are more
The Branches of the Tree of Life:
● Carl Woese proposed a new taxonomic category called the domain to represent
the major groups.
○ Woese proposed three major groups of organisms: two groups are
prokaryotic (bacteria and archaea) and one is eukaryotic (eukarya).
○ The location of some branches on the tree is hotly debated and the shape
of the tree will continue to change as databases expand.
● Biologists test ideas about the way the natural world works by testing the
predictions made by possibly multiple precisely and concisely formulated
● Good scientific hypotheses make testable predictions - predictions that can be
rejected (for instance, falsified) by collecting and analysing data obtained in
carefully designed experiments.
● Effective experimental designs allow researchers to test effects from single, well-
defined factors on phenomena and also:
○ Comprise control groups
○ Involve constant or equivalent conditions among groups (except for the
treatments to be tested)
○ Include repeating the experiment
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