D5 Phylogeny and Systematics Flashcards Preview

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Flashcards in D5 Phylogeny and Systematics Deck (11)
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Outline the value of classifying organisms

• Allows us to distinguish between and compare organisms
• Makes it easier to identify organisms
• Makes it easier to collect, sort and store information about organisms
• Shows how closely organisms are related and suggests evolutionary links
• Allows predictions to be made about characteristics of members of a group


Explain the biochemical evidence provided by the universality of DNA and protein structures for the common ancestry of living organisms

• The genetic code is universal
• All organisms use DNA and/or RNA as their genetic material
• The same four bases are used
• The same codons code for the same amino acids
• All living organisms use the same 20 amino acids for protein synthesis


Explain how variation in specific molecules can indicate phylogeny

• Phylogeny is tracing evolutionary links and origins by comparing similar molecules from different species
• Variations in these molecules (either base or amino acid sequence) will occur due to mutations which accumulate over time
• The greater the differences between the common molecules, the longer the time span since the two species had a common ancestor
• Mitochondrial DNA is useful for tracing phylogeny as it is inherited via the maternal line, lacks recombination and has a known mutation rate


Outline how biochemical variation can be used as an evolutionary clock

• Some genes accumulate mutations at a relatively constant rate
• If this rate of change is known, scientists can calculate the time of divergence between two species based on the number of differences


Discuss limitations of the evolutionary clock concept

• The rate of change can differ for different groups of organisms (e.g. animals and plants)
• The rate of change can vary between different genes
• Over long periods, earlier changes may be reversed by later changes


Define clade

 A group of organisms all descended from a common ancestor


Define cladistics

A method of classification of living organisms based on the construction and analysis of cladograms


Distinguish between analogous and homologous structures

Analogous from different ancestor (convergent evolution), homologous come from common ancestor (divergent evolution.
Analogous have similar function but different structure, homologous don't have similar function but do have similar structure.


Give an example of analogous characteristics

Wings in bats, birds, insects


Give an example of homologous characteristics

Pentadactyl limb in vertebrates


Discuss the relationship between cladograms and the classification of living organisms

• Classification was traditionally based on morphology (structural characteristics)
• Methods used to construct cladograms typically utilise a different approach (e.g. molecular data - more objective)
• Cladograms can show ancestral relationships and reflect how recently two groups shared a common ancestry
• As such they should be considered a good complement to traditional classification schemes
• In some cases, cladograms have lead to revisions in scientific classifications