Chapter 17 Study Guide
We will focus on only a few key concepts from this chapter. You should already be familiar with many of these concepts from other courses.
1. It is believed that the first organisms appeared on Earth around 3.8 billion years ago. What evidence do each of the following for this occurrence?
-the earliest forms of lfe for which we have clear fossil evidence
-a bulbous mass of sedimentary layers of limestone accreted by microbes over years
-within the outer layers, microbes grow as a microbial mat (sort of like a biofilm)
-outer laters of mat contain oxygenic phototrips that exude bubbles of oxygen
-a few mm below surface, red light ...view middle of the document...
View the animation “Phylogenetic trees” to refresh your memory about cladograms. These trees make the assumption that the rate of nucleotide change is constant. For each of the following explain why this is not always true.
• sequences that code for functional genes change slower
• genes in rapidly replicating organisms change faster
• different environments result in different selective pressur
-functional sequences change slower→ why?
-functinal sequences: code for structures: ribosomes→ differ because theyre more important and the organism can’t survive if they change
-selective pressure: genes that provide desireable genes
phylogenetic tree: estimates the relative amounts of evolutionary divergence between the sequences
-if divergence rate over time or mutation rate is the same for all sequences compared, then divergence data can be used to infer the length of time since two species shared a common ancestor
-Maximum Parsimony: evolutionary distances are computed for all pairs of taxa based on the numbers of nucleotide or amino acid substitution between them
- a proposed common ancestor is reconstructed, all possible trees comparing relative time of divergence from the common ancestor are computed
-the best fit tree is the one with the fewest mutations to fit the fata
Maximum Liklihood: for each possible tree, the likelihood that such a tree would have produced the observed DNA sequences
-the probability of given mutations is based on complex statisrical calculations
-require large amouns of computation but obtain the most info from the data
3. Compare the three domains of life. Traditionally trees of life have shown the Domain Bacteria branching off first (Figure 17.21), then the Arachea branching off later from the lineage leading to the Domain Eukarya. Use the information summarized in Table 17.2 to explain the evidence that supports this hypothesis.
-archaea are roughly as distant from bacteria as eukaryotes
-thee domans → Woese
-root of the tree: compare a pair of homologous genes wth one organims, homologs that diverged from a common ancestral gene and acquired distant functions
-most phylogenetic data so far indicate a root between Bacteria and the common ancestor of Archaea and Eukarya
-thus Bacteria diverged before Archaea and Eukarya diverged from each other
-All domains have distinctive traits absent of scarce in the other two
Eukaryotes: have nucleus and complex membranous organelles
-mitrochondira and chloroplasts which evolved from internalized baceria
-bacteria and archaea have no nucleus and have relatively simple intracellular membranes
-size is limited by diffusion across the cell membrane with occasionall exceptions
-the larger size and complexity of eukaryotic cells generally require the most high-powered sources of energy such as aerobic respiration and oxygenetic photosynthesis although some protists conduct fermentation
-prokaryores have a wider...