Download Shared character

17-2 Systematics
-
Goal is to categorize organism by NATURAL relationships
PHYLOGENETICS
So systematic taxonomists think organism’s classficiation should reflect PHYLOGENY
Phylogeny – evolutionary history of a species/taxon
-
Today’s taxonomists involved in phylogenetics – analyzing evolutionary/ancestral correlation between taxa
Evidence to predict about phylogenetics
o
o
o
They compare visible similarities – between living and fossilized creatures
Patterns in embryonic development - how diff species embryos can express similar genes
Compare chromosomes, DNA, RNA, macromolecules from diff species
This can be modeled through phylogenetic diagram/tree – shows how closely related some taxa can be.. keep in mind its
subject to change when scientists find out new things!
EVIDENCE OF SHARED ANCESTRY
-
Fossils are good for finding evolutionary changes, but there’s not much evidence for small/softbodied (worms,
bacteria, fungi)
o Can help with phylogenetic diagram, but systematist tests inferred relationships for more evidence
 Systematists will look at Homologous features ( sharing common ancestry)
 Jaws of pangolin and dog
 Analogous features (similar because of similar function, not lineage)
 Scales – pangolin& dog, but they both evolved independently in 2 taxa
 Embryological evidence
 Fluid-filled sac, amnion, surrounds embryos of birds/reptiles/mammals – this shared
feature combines them into one taxon, excluding other vertebrates
CLADISTICS
-
SYSTEM for phylogenetic analysis – using only shared/derived characterists to group taxa
o
o
Shared character – one that all members of a group have in common –
Derived character – one that evolved ONLY within group

-
Birds- feathers- only animals with feathers between living & fossils
 So the feathers were evolved only within bird line, not common ancestor
Clade- group of organisms including ancestor and all descendants
o No category names (class, phylum)
Cladists make cladograms – their own phylogenetic diagrams
o They have strict guidelines, so their taxonomies can be a little different from traditional
Traditional taxonomists will place crocs with
lizards and turtles in reptilia class, and birds
in aves class
But cladists put crocs and birds together in a
clade because their common ancestor is
more recent
-
Then it’s linked with successively
later clades
CONSTRUCTING A CLADOGRAM
-
Start with the outgroup – the organism distantly related to the other organisms
1. choose organisms—they go in left column, and put the outgroup there too. Top, going right, characteristics they
could share
2. score the organisms lacking certain characteristic 0, and if it has it, score 1
3. most commonly shared derived character (this case vascular tissues) goes at the base of 1st branch of cladogram
- 2nd most common; seeds, 3rd common; flowers
- ferns lack seeds, that’s why they go on second branch
Pine trees lack flowers; so third branch. And flowering plants go on last branch
*so this tree is a cladistic hypothesis of the evolultionary relationship between these plants
Cladists can also look at
molecular level characteristics,
or even a nucleotide in a gene
sequence, or a protein’s amino
acid sequence
MOLECULAR CLADISTICS
Take the common characteristics.. separate
into thea diff
charactersitsica
– derived.. between species by making a tree
Just by looking at the amino acid sequences,
biologist
can find relationships
characteristics that makes it differ
Molecular cladogram- branch lengths proportional to #of amino acid changes
Shared characterists – the ones that
everyone shares…
-
DOESN’T depend on any physical sims/diffs!!
Molecular clock  used to estimate sequence of past evolutionary events
-
Biologists use Evol. Changes of macromolecules (like DNA, RNA, proteins) as form of mol.. clock
Molecular clock hypothesis - suggests that greater diff in sequences- more distant common ancestor
-
Carefully matched molecular clock with fossil records- can be used to hypothesize when characteristics arose
and organisms diverged from their ancestors.
CHROMOSOMES
-
Karyotypic data – doesn’t depend on molecular nor physical
When the chromosomes are stained, showing pattern of bands, and those band have same pattern in same
region of similar chromosomes, the regions are likely to have been inherited from 1 chrom. In last common
ancestor of 2 species
o When chromosomes have similar banding patterns, they may be homologous
 Here B2 and B3 together are supposed to seem homologous to A2
 In this case, biologists can still hypothesize that they all came from common ancestor
Pangolin classification – pangolins share adaptations with
aardvarks&anteaters but they’re analogous. More analysis
Scientists use all diff info to make their phylogenetic models shows their skeletal structure and nucleotide sequence are all
on diff branches on this mammalian phylogenetic tree. So
- Physical features
the pangolins are put closer to dogs & bears than aard &anteaters
- Embryos
- Genes in nucleus
- Mitochondrial DNA
- Ribosomal RNA