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Chapter 9 Eukaryotic Cells and Multicellular Organisms. Figure CO: Oblong shaped Giardia. Courtesy of Dr. Stan Erlandsen/CDC. Overview. The origin of cells with eukaryotic organization, some 2.5 Bya, facilitated the evolution of multicellularity
Figure CO: Oblong shaped Giardia
Courtesy of Dr. Stan Erlandsen/CDC
Figure 01A: Microfossils of probable eukaryotic cells
Figure 01B: Microfossils of probable eukaryotic cells
Figure 01C: Microfossils of probable eukaryotic cells
Reproduced from Schopf, J.W., Scientific American 239 (1978): 111-138. Courtesy of J. William Schopf, Professor of Paleobiology & Director of IGPP CSEOL
Figure 02: Phylogenetic tree
Adapted from Hori, H. and S. Osawa, Proc. Natl Acad. Sci. USA 76 (1979): 381-385.
Others would establish six supergroups
Figure B01: Eukaryotic tree of life
Adapted from Keeling, P.J., et al., Trends Ecol. Evol. 20 (2005): 670-676.
red and green algae
Figure B03: Diversity of forms of foraminiferans
Reproduced from E. Haeckel. Art Forms in Nature. New York: Dover Publications, Inc., 1974.
cellular slime mold
plasmodial slime mold
As more data is collected, especially DNA sequence data, from more example organisms, and more data about Horizontal Gene Transfer, these groups will be revised -- probably many times.
Figure B02: Eukaryotic tree of life
Adapted from Adl, S.M., Simpson, A.G.B., et al., J. Eukaryot. Microbiol. 52 (2005): 399-451.
Lots of competing hypotheses!
We may never know the correct pathway or how many steps were involved.
Endosymbiosis is very likely an important part of this process.
Which came first: the nucleus, mitochondria or chloroplasts as organelles?
Figure 03: Symbiotic relationships between a eukaryote and its photosynthetic organelles
The ciliate Paramecium bursaria houses hundreds of symbiotic green algae which can be liberated from the Protistan cell and will live independently
Courtesy of Anthony L. Swinehart, Hillsdale College
The Origin of early Eukaryotic Ancestors leading to the lineages of animals and fungi was probably an independent event from that of the origin of plants
Figure 04: Primary, secondary and tertiary endosymbiosis
Adapted Cracraft, J. and M. J. Donoghue (Eds). Assembling the Tree of Life. Oxford University Press, 2004.
When a stretch of DNA serves as molecular clock, it becomes a powerful tool for estimating the dates of lineage-splitting events
Mitochondrial DNA and Ribosomal RNA Provide Two Types of Molecular Clocks
Mutations add up at a fairly
constant rate in the DNA of species that evolved from a common ancestor.
Ten million years later—
one mutation in each lineage
Another ten million years later—
one more mutation in each lineage.
The DNA sequences from two
descendant species show mutations
that have accumulated (black).
The mutation rate of this
sequence equals one mutation
per ten million years.
DNA sequence from a
Mitochondrial DNA is
passed down only from
the mother of each generation, so it is not subject to recombination.
Nuclear DNA is inherited from both
parents, making it more difficult to
trace back through generations.Organelle DNA as a Molecular Clock
The study derived from a lock of hair collected by a British anthropologist one hundred years ago from an Aboriginal man from the Goldfields region of Western Australia in the early 20th century
Figure B04A: The polymerase chain reaction
Which came first – nucleus or organelle? Other details of the transition?
The same basic components and organelles as the plant cell but the substitution of a chitin cell wall and no central water vacuole
years of strictly