Lecture 5: Traits used for classification Flashcards
How are traits used in classification
to compare organisms
Morphological traits (shapes of the body)
- Overall bodily shape such as ‘having four legs’
- Tissues, such as bones and branches
*Individual cells, especially for unicellular organisms
*Organelles such as the nucleus and chloroplast (photosynthesis)
Biochemical traits
Presence and absence of metabolic pathways etc.
Genetic traits
- Presence and absence of related genes
- Differences in those genes
In general, organisms which share similar traits are ___
likely to be evolutionary related to one another
What trait is used a lot for classification?
- Skull morphology is used a lot for classification due to its complexity
- It is less likely for complicated traits to evolve independently in unrelated organisms and end-up looking near-identical by chance
Similar morphology does not always mean
close relatedness
Australian mole and North American mole look very similar however __
- Australian mole is marsupial
- North American mole is placental
- Evolved under selective pressure for their ground-burrowing lifestyle
- These species are not closely related at all
- Diverged~140-160 million years ago
ancestral mammal
Convergent evolution
Unrelated lineages of organisms can develop similar-looking traits independently
Homology
similar traits in organisms shared through common ancestry
All mammals feed infants with ___ implying ___
milk
* This suggests that the ancestral mammal already had the milk-feeding trait which got passed to all members of its lineages
_____ is said to be a homologous trait
‘Feeding milk’
Analogy
similar-looking trait in organisms which occurred not by shared ancestry
Mole-like trait is not seen in all mammals meaning
- Ancestral mammal probably did not have mole-like traits
- Mole-like traits developed independently in Australian and Placental moles lineages, and ended up looking alike
The mole-like trait is ___
analogous
Shared ancestral character
trait held by the common ancestor which got passed on to all* descendants
___ is a shared ancestral character for all mammals
‘Feeding milk’
Shared derived character
a unique character found in a lineage which developed after the common ancestor diverged
‘Bag for infants’ __
is a homologous trait for marsupials
_____ is a shared derived character, unique to marsupials
‘Bag for infants’
Shared ancestral/derived characters are ___ terminologies
relative
* It changes depending on who you set as the common ancestor
If you choose the common ancestor of all mammals as the reference, “bag for infants” is a ____ trait
‘Bag for infants’ is a shared derived character unique to marsupials
If you choose the common ancestor of marsupials as the reference, “bag for infants” is a ____ trait
‘Bag for infants’ is a shared ancestral character
The ‘milk-feeding’ trait of mammals becomes a ____ in reference to all vertebrates
shared derived character
‘Having a backbone’ is a __ if you are referring to Vertebrae
shared ancestral character
The ancestral chordate is a __ in the tree of life
local, shared-derived trait
Different lineages of marine mammals
- Dolphins and Whales
- Seals
- Manatees
- These traits are shared derived characters in relation to entire mammals
Are Marine lineages homologous or analogous?
These traits are analogous to each other since they were acquired independently in their lineages
Very complicated traits are __ in multiple independent lineages by convergent evolution
unlikely to emerge
Example of homologous structure in humans and birds
- ‘Forelegs’ of humans and birds share clear similarities
- Very low chance for these structures to match to this extent if they have evolved independently
- Forelegs of humans and birds are homologous (shared ancestry)
Differences in structure between bats and birds
- Birds have reduced digits (Metacarpals/Phalanges) with feathers attached to the forelimb
- Bats have elongated digits which sustains a membrane, like an umbrella
Are the wings of bats and birds homologous or analogous?
- Wings of birds and bats are analogues
- The ancestral ‘foreleg’ structure evolved independently in two different lineages to give rise to a flying mechanism
- This ended up giving rise to ‘somewhat- similar’ morphologies
Similarities and differences in structures give hints to
evolutionary relatedness of organisms
___ does not always correspond to evolutionary distance
Different morphology
Small change in a ___ can lead to huge diversity in ____
gene (genotype)
morphology (phenotype)
____ are used in combination to deduce phylogeny
Morphologies and genes
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 inherits 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
Ex of Ortholgous genes
- Example: common ancestor speciates into Humans and Chimpanzees
- Both species inherit ‘Gene_A Ancestor’
- Overtime, the ancestral gene evolves into:
- ‘Gene_A Human’ in Humans
- ‘Gene_A Chimps’ in Chimpanzees
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
Can evolutionary relationships be deduced when looking at paralogous genes in a gin organism?
You can not deduce evolutionary relationship between species if you are only observing paralogous genes within the same organism
Typically, genes with important functions __
evolve slowly
* Higher chance for a mutation to be detrimental to the organism
* Lower frequency of accumulating mutations
Ex of genes that evolve slowly
The 16S and 18S ribosomal RNA genes, used for translating mRNA into proteins, evolve especially slowly and are the gold- standards for molecular phylogeny
Use faster-evolving genes to analyze
more-recent evolutionary events
Slower-mutating genes may not accumulate mutations quickly enough to observe recent evolutionary events
Use slower-evolving genes to compare evolution
over longer period of time
Faster-evolving genes accumulate too many mutations for a long-term comparison
