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Cladistics
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Learning objectives Define clade
Explain how genetics and base sequencing can be used to determine the clade that an organism belongs to Explain how base sequencing can be used to determine the point at which two species diverged from a common ancestor Sketch a cladogram Explain how our understandings of cladistics does not always correspond to the structural classification of some organisms
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Key words Morphology- the study of the structure of an organism
Phylenology- the evolutionary history of a species Phylogenetic tree- shows the phylenology of a species Parsimony- the least number of evolutionary events (the simplest version)
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Learning objectives Define clade
Explain how genetics and base sequencing can be used to determine the clade that an organism belongs to Explain how base sequencing can be used ti determine the point at which two species diverged from a common ancestor Sketch a cladogram Explain how our understandings of cladistics does not always correspond to the structural classification of some organisms
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Cladistics is- the classification of organisms based upon its branching from a common ancestor (biological lineage) Clade- a group of organisms that have evolved from a common ancestor Cladistics is also known as- phylogenetic systematics
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Learning objectives Define clade
Explain how genetics and base sequencing can be used to determine the clade that an organism belongs to Explain how base sequencing can be used to determine the point at which two species diverged from a common ancestor Sketch a cladogram Explain how our understandings of cladistics does not always correspond to the structural classification of some organisms
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DNA/Base and amino acid/protein sequencing-
The modern day techniques of DNA/Base sequencing and amino acid/protein sequencing are used to establish members of a clade. Organisms that have recently evolved from a common ancestor will have few differences in their base or amino acid sequences. Organisms that evolved much earlier will have a much more varied DNA and amino acid sequence The greater the difference in DNA and amino acid sequence the earlier the organisms evolved from their ancestor Check out
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Learning objectives Define clade
Explain how genetics and base sequencing can be used to determine the clade that an organism belongs to Explain how base sequencing can be used to determine the point at which two species diverged from a common ancestor Sketch a cladogram Explain how our understandings of cladistics does not always correspond to the structural classification of some organisms
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Sequencing databases Vast databases now exist that contain information on the DNA and amino acid sequence of thousands of organisms. These databases can be analysed to determine which organisms belong to the same clade
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Example of predicting divergence
70,000 years 140,000 years By sequencing the mitochondrial DNA from organisms that are known to be closely related we can predict when divergence from a common ancestor may have occurred. 5 million years In order for this to work we look at the number of variances in the DNA sequence that are down to mutations. As mutation are believed to occur at a constant rate we can predict how many years a species deverged fron an ancestor.
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Learning objectives Define clade
Explain how genetics and base sequencing can be used to determine the clade that an organism belongs to Explain how base sequencing can be used to determine the point at which two species diverged from a common ancestor Sketch a cladogram Explain how our understandings of cladistics does not always correspond to the structural classification of some organisms
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Cladogram- a tree diagram showing the most probable sequence of divergence
The point at which two or more species diverge is called node. Much of our modern day understanding of cladistics has been influenced by algorithms and computer predictions
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Learning objectives Define clade
Explain how genetics and base sequencing can be used to determine the clade that an organism belongs to Explain how base sequencing can be used to determine the point at which two species diverged from a common ancestor Sketch a cladogram Explain how our understandings of cladistics does not always correspond to the structural classification of some organisms
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Problems with cladistsics
It is often difficult to distinguish if a characteristic has formed from divergent or convergent evolution and therefore if it is a homologous or analogous trait. Because of this many organisms have been misclassified and placed in to the same clade as organisms that have a similar morphology. Base and amino acid sequencing are therefore now more favoured techniques for grouping organisms- example Figworts
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Producing a cladogram 5 closely related organisms were studied in order determine where and when he species diverged from each other look at the data in the table Characteristic Ancestral Species A B C D Av. wing span 30cm 50cm Eye colour Green Blue Toe formation Separate digits Webbed Markings Striped Spotted Egg shell colour Grey White Beak shape Rounded Pointed Blank table
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Producing a cladogram Ancestral characteristic = 0
Ancestral Species A B C D Av. wing span 30cm 50cm Eye colour Green Blue Toe formation Separate digits Webbed Markings Striped Spotted Egg shell colour Grey White Beak shape Rounded Pointed Characteristic Ancestral Species A B C D Av. wing span 30cm Eye colour Green Toe formation Separate digits Markings Striped Egg shell colour Blue Beak shape Rounded Ancestral characteristic = 0 Derived characteristic = 1
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Producing a cladogram 5 closely related organisms were studied in order determine where and when he species diverged from each other look at the data in the table Characteristic Ancestral Species A B C D Av. wing span 30cm 1 Eye colour Green Toe formation Separate digits Markings Striped Egg shell colour Blue Beak shape Rounded
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Identify where in the cladogram the grey egg colour, pointed beak and the webbed feet may have evolved Characteristic Ancestral Species A B C D Av. wing span 30cm 50cm Eye colour Green Blue Toe formation Separate digits Webbed Markings Striped Spotted Egg shell colour Grey White Beak shape Rounded Pointed
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