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5.4: Cladistics

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Define "clade."


Understanding: A clade is a group of organisms that have evolved from a common ancestor.
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Define "clade."


Understanding: A clade is a group of organisms that have evolved from a common ancestor.
A clade is all of the organisms hypothesized to have evolved from a common ancestor. A "branch" on the tree of life.

In the example, crocodiles and birds are a in the same clade. Snakes and crocodiles are not in the same clade unless you also include birds, lizards and tuatara.
Image: *Define "clade."* Understanding: A clade is a group of organisms that have evolved from a common ancestor.
Define "cladistics."


Understanding: A clade is a group of organisms that have evolved from a common ancestor.
Cladistics is a way of classifying organisms into groups based on shared characteristics and common ancestry. Species in the same group (clade) are more closely related (share a more recent common ancestor) to members of the same group than to other organisms.
Image: *Define "cladistics."* Understanding: A clade is a group of organisms that have evolved from a common ancestor.
Outline the relationship between time, evolutionary relationships and biological sequences.


Understanding: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
Mutations in the nucleotide base sequences of DNA, and therefore differences in the amino acid sequence of proteins, accumulate gradually over time.

Therefore, the more differences there are in biological sequences, the more time has passed for the differences to accumulate. The more time that has passed since organisms have shared a common ancestor, the less evolutionarily related the organism are to each other.

Visa versa: the less differences there are in biological sequences, the less time has passed for the differences to accumulate. The less time that has passed since organisms have shared a common ancestor, the more evolutionarily related the organism are to each other.
Image: *Outline the relationship between time, evolutionary relationships and biological sequences.* Understanding: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
Summarize the use of DNA sequences as evidence for evolutionary relatedness between species.


Understanding: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
The DNA base sequences of the same gene in different species is compared. Because mutations (differences) in the DNA sequence will accumulate over time, the species with more similarities in the base sequence are likely more closely related (meaning they have a more recent common ancestor; have diverged from their common ancestor more recently) than species with more differences in the base sequence. The percent similarity between species can be used as the basis for creating a cladogram of hypothesized evolutionary relationships.
Image: *Summarize the use of DNA sequences as evidence for evolutionary relatedness between species.* Understanding: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
Summarize the use of amino acid sequences as evidence for evolutionary relatedness between species.


Understanding: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
The amino acid sequences of the same protein in different species is compared. Differences in the amino acid sequences are due to mutations of the DNA. Because DNA mutations (and in turn amino acid sequences) will accumulate over time, the species with more similarities in the amino acid sequence are likely more closely related (meaning they have a more recent common ancestor; have diverged from their common ancestor more recently) than species with more differences in the amino acid sequence. The percent similarity between species can be used as the basis for creating a cladogram of hypothesized evolutionary relationships.
Image: *Summarize the use of amino acid sequences as evidence for evolutionary relatedness between species.* Understanding: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.