Topic 5.4: Cladistics

Question 1

Cladistics definition

Answer 1

Classification of organisms into groups of species (clades)

Question 2

Clade definition

Answer 2

Group of organisms that have evolved from a common ancestor (Clade = Ancestral organism + All evolutionary descendants)

Question 3

Cladograms definition

Answer 3

Tree diagrams that show the most probable sequence of divergence in clades

Question 4

Elements of cladograms (4)

Answer 4

a) Root
b) Node
c) Outgroup
d) Clade

Question 5

Root

Answer 5

Initial ancestor common to all organisms within a cladogram

Question 6

Node

Answer 6

Hypothetical common ancestor that speciated to more taxa

Question 7

Outgroup

Answer 7

The most distantly related species in the cladogram

Question 8

Clade

Answer 8

A common ancestor and all of its decendants

Question 9

Construction of cladograms using structural evidence (2)

Answer 9

1) Organize selected organisms according to defined characteristics
2) Sequentially order organisms according to shared characteristics to construct a cladogram
a) Each characteristic is represented by a node, with more common characteristics representing earlier nodes

Question 10

How have cladograms been constructed historically?

Answer 10

Based on structural characteristics

Question 11

Why is it not reliable to establish evolutionary connections based on structural characteristics? (2)

Answer 11

a) Closely related organisms can exhibit very different structural features (homologous) due to adaptive radiation
b) Distantly related organisms can display very similar structural features (analogous) due to convergent evolution

Question 12

Homologous traits (5)

Answer 12

a) Similar internal structure
b) Different external structure due to selection pressures
c) Species have a common ancestry
d) Evidence for divergence evolution
e) Pentadactyl limb

Question 13

Analogous traits (5)

Answer 13

a) Different internal structure
b) Similar external structure due to common selection pressures
c) Species do not share a common ancestry
d) Evidence for convergent evolution
e) Wings in insects, birds, and bats

Question 14

How are cladograms being constructed nowadays?

Answer 14

Biochemical evidence (DNA / Amino acids)

Question 15

What demonstrates the degree of evolutionary divergence between two species?

Answer 15

The number of differences between compatible base sequences

Question 16

A greater number of differences between comparable base sequences suggest…

Answer 16

more time has passed since two species diverged

Question 17

The more similar the base sequence of two species are, …

Answer 17

the more closely related the two species are expected to be

Question 18

Using DNA / RNA sequences to construct cladograms (2)

Answer 18

a) To compare closely related organisms

b) Mutations occur more readily in non-coding sequences than in gene sequences

Question 19

Using amino acid sequences to construct cladograms (2)

Answer 19

a) To compare distantly related species

b) Slowest rate of change due to degeneracy

Question 20

What happens if a sequence accumulates mutations at a constant rate?

Answer 20

There is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.

Question 21

Clade reclassification of figworts

Answer 21

a) It was the 8th largest family of angiosperms
b) After examining a chloroplast gene, they decided to split the figworts into 5 different clades and become into the 36th largest group