lecture 19- tree building and tree thinking Flashcards
phylogenetic tree
visualizing relatedness of organisms
node
point on phylogenetic tree showing two organisms share a common ancestor
root to tip distance on phylogenetic tree
portrays the passage of time
fewer distances= more closely related= shorter root to tip distance to common ancestor
history of aids
history of hiv: origins of strains
hiv is close to siv (disease impacting primates)
siv likely mutated into hiv and then entered the human population
phylogenetic trees are used to understand evolutionary origins and relationships of different hiv strains (hiv 1, america and hiv 2, west africa)
parsimony
take the most simplistic answer
outgroup
nearby related but distinct species
convergent evoluation
can lead to the emergence of traits multiple times in the phylogenetic treee
convergence
the process whereby distinct species independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
shared ancestry
share a common ancestor
convergence
the tendency of unrelated animals and plants to evolve superficially similar characteristics under similar environmental conditions.
steps of drawing a phylogenetic tree
1) identify dna sites that differ between organisms
2) count dna differences between two organisms, do for all pairings between organisms to make full chart
3) identify closest pair (ones with least differences in chart)
4) draw closest pair into tree, separated by correct distance (Distance/2)
5) combine closest pair into one column and recalculate distances (average)
6) repeat tree drawing using next closest pair
7) repeat column combining with next closest pair
why might our tree differ from the accepted tree
1) we only used a small amount of dna sequence
2) we used dna sequence from one area of the genome
3) rates of dna sequence changes vary across the genome
4) rates of dna sequence changes vary between species
why is 16s ribosomal dna useful to study the microbiome