lecture 19- tree building and tree thinking

Question 1

phylogenetic tree

Answer 1

visualizing relatedness of organisms

Question 2

node

Answer 2

point on phylogenetic tree showing two organisms share a common ancestor

Question 3

root to tip distance on phylogenetic tree

Answer 3

portrays the passage of time
fewer distances= more closely related= shorter root to tip distance to common ancestor

Question 4

history of aids

Answer 4

Question 5

history of hiv: origins of strains

Answer 5

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)

Question 6

parsimony

Answer 6

take the most simplistic answer

Question 7

outgroup

Answer 7

nearby related but distinct species

Question 8

convergent evoluation

Answer 8

can lead to the emergence of traits multiple times in the phylogenetic treee

Question 9

convergence

Answer 9

the process whereby distinct species independently evolve similar traits as a result of having to adapt to similar environments or ecological niches

Question 10

shared ancestry

Answer 10

share a common ancestor

Question 11

convergence

Answer 11

the tendency of unrelated animals and plants to evolve superficially similar characteristics under similar environmental conditions.

Question 12

steps of drawing a phylogenetic tree

Answer 12

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

Question 13

why might our tree differ from the accepted tree

Answer 13

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

Question 14

why is 16s ribosomal dna useful to study the microbiome

Answer 14