5.4 Cladistics

Question 1

Cladistics

Answer 1

the new branch of taxonomy that classifies organisms in terms of their place in the evolutionary tree based on shared characteristics with a common ancestor

Question 2

Clade

Answer 2

is a group of organisms that evolved from a common ancestor
consists of an ancestral organism and all of its evolutionary descendants
Members of a clade will possess common characteristics as a result of their shared evolutionary lineage

Question 3

Cladograms

Answer 3

Cladograms are tree diagrams where each branch point represents the splitting of two new groups from a common ancestor

Question 4

Molecular clock

Answer 4

Some genes or protein sequences may accumulate mutations at a relatively constant rate (e.g. 1 change per million years)
If this rate of change is reliable, scientists can calculate the time of divergence according to the number of differences

Question 5

Molecular clock limitations

Answer 5

Different genes or proteins may change at different rates
The rate of change for a particular gene may differ between different groups of organisms
Over long periods, earlier changes may be reversed by later changes, potentially confounding the accuracy of predictions

Question 6

Mitochondrial DNA used for molecular evidence

Answer 6

DNA in the mitochondria of all cells
female line only
easy to find mutations
short and cheap (doesn’t take long to process)

Question 7

Y chromosome DNA

Answer 7

accumulates more mutations than other chromosomes
ancestry of male lines can be determined

Question 8

Amino acid analysis

Answer 8

amino acid sequences may be used for comparison but have the slowest rate of change due to codon degeneracy
typically used to compare distantly related species

Question 9

Structural evidence

Answer 9

Historically, classification was based primarily on morphological differences (i.e. structural characteristics)
Closely related species were expected to show similar structural features, indicating common ancestry

Question 10

Structural evidence limitations

Answer 10

Closely related organisms can exhibit very different structural features due to adaptive radiation (e.g. pentadactyl limb)
Distantly related organisms can display very similar structural features due to convergent evolution

Question 11

Reclassification

Answer 11

evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species

Question 12

Figworts reclassification

Answer 12

reclassified based on molecular evidence (DNA analysis of the chloroplast gene)