Lecture 5 Flashcards
Traits used to classify species
Morphological traits (shapes of the body)
- Bodily shape (4 legs)
- Tissues
- Individual cells
- Organelles
Biochemical traits
- Presence and absence of metabolic pathways
Genetic traits
- Presence and absence of related genes and the differences in those genes
In general organisms which share similar traits are likely to be
Evolutionary related to one another especially when the shared trait is a complicated bone structure
It is less likely for complicated traits to
Evolve independently in unrelated organisms and end up looking near identical
Why is skull morphology used
It is used for classification due to its complexity
Example of how morphology does not always mean relatedness
Australian mole and north american mole may look very similar but australian is marsupial and north american is placental - not closely related
Convergent evolution
Unrelated lineages of organisms can develop similar looking traits independently
Not all marsupials and placentals look like moles which means that the mole like trait was not in the common ancestor but evolved independently after those lineages split
Homology
Similar traits in organisms shared through common ancestry
- All mammals feed infants with milk, suggests that the ancestral mammal had milk feeding trait that got passed down
Analogy
Similar looking trait in organisms which occurred not by shared ancestry
Mole like trait not seen in all mammals which developed independently
Shared ancestral character
Trait held by the common ancestor that got passed on to all descendants
Shared derived character
A unique character found in a lineage which developed after the common ancestor diverged
- Bags for infants in marsupials developed in their lineage after ancestral mammal diverged
Shared ancestral/diverged characters are
Relative terminologies - changes depending on who you set as the common ancestor
“infant bags” - derived character if mammals are used as a reference
- Ancestral character is marsupials are used as reference
Convergent evolution in marine mammals
Different lineages of marine mammals
Traits are shared derived characters in relation to entire mammals
Traits are analogous to each other since they were acquired independently in their lineages
Forelegs of humans and birds are
Homologous - shared ancestry
How are wings of birds and bats analogues
Birds have reduced digits with feathers attached
Bats have elongated digits which sustain a membrane
Foreleg structure evolved independently in two different lineages to give rise to a flying mechanism - ended up giving rise to somewhat similar morphologies
Similarities and differences in structures give
hints to evolutionary relatedness of organisms
Example of how different morphology does not always correspond to evolutionary distance
Hawaiian silversword plants have very different morphologies but they are only 5 million years apart
- Small change in a gene (genotype) can lead to a huge diversity in morphology
Taxonomy using molecular genetics
- Any organism contains multiple genes in their genome
- Different organisms frequently have related genes which they acquired through shared ancestry: homologous genes
Homologous genes can be used to deduce evolutionary relationship between organisms based on how similar/different their sequences are
Orthologous genes
A common ancestor diverges into two species. Both species inherit the same genes from their ancestor (homologous genes with shared ancestry)
Since they are in a different lineage, the homologous genes can now begin to evolve (mutate) differently
Example with chimp and humans about Orthologous genes
Both species inhert GAancestor. Over time, gene evolves to Gene Ahuman in humans and Gene Achimps in chimps
Paralogous genes
A gene makes a copy of itself within the same species
The two copies of genes (in the same species) can begin to evolve differently
Note: You can not deduce evolutionary relationship between species if you are only observing paralogous genes within the same organism
Genes with important functions evolve
Slowly
- Higher chance for a mutation to be detrimental to the organism
- Lower frequency of accumulating mutations
What RNA genes evolve slowly
The 16S and 18S ribosomal RNA genes, used for translating mRNA into proteins, evolve especially slowly
why are faster evolving genes used to analyze more recent evolutionary events
- Slower-mutating genes may not accumulate mutations quickly enough to observe recent evolutionary events
- For example: Can not use slow GeneA to compare evolution after 20 million years, since it remains the same for the first 40 - 50 million years after speciation
- Fast GeneB has accumulated enough mutations after 20 million years for comparison
Why are slower evolving genes used to compare evolution over longer period of time
- Faster-evolving genes accumulate too many mutations for a long-term comparison
- After 100 million years, fast GeneB have changed too much from the original sequence; two species have
lost their resemblance completely and therefore, this data can not be used for comparison - Slow GeneA still retains similarities after 100 million years
