5.4 - Cladistics

Question 1

what are clades?

Answer 1

• a group of organisms that have evolved from a common evolutionary ancestor.
• members of a clade will share common characteristics
• some clades contain many species whereas others have only one

Question 2

what does molecular sequencing do?

Answer 2

• using genetic material or protein sequences it can determine the evolutionary origins of a species
• species less related will have more genetic or protein differences

Question 3

how are mutations a molecular clock?

Answer 3

• differences in base sequence of DNA mean gradual accumulation of mutations.
• rate of mutations happens at a constant rate so can be used as a molecular clock
• no. of differences in base sequence indicates when species were split from ancestor

Question 4

limitations to the molecular clock idea?

Answer 4

• different genes or proteins have different mutation rate
• rate can change for particular gene
• early mutations may have reversed.

Question 5

How are structural traits used?

Answer 5

• used to determine clades but less common bc some features don’t connect
• similarities are categorised as either homologous or analogous traits

Question 6

what are homologus structures?

Answer 6

traits derived from a common ancestor
- it is an example of divergent evolution: pentadactyl limbs

Question 7

what are analogous structures?

Answer 7

• superficial and derived through separate evolutionary pathways but bc of similar natural selective pressures they adapt similar structures.
• is an example of convergent evolution: wings

Question 8

what is a cladogram?

Answer 8

• a tree diagram that shows the similarities and differences between the species in a clade
• each branching point (a node) represents the splitting of two new groups from a common ancestor, also shows a speciation event occurred due to divergent evolution
• based on base sequence or amino acid sequence of species

Question 9

the primate cladograms

Answer 9

• all primates belong to the same clade: Hominoids
• humans are most closely related to chimpanzees and bonobos

Question 10

what are cladistics?

Answer 10

• analysis done by computer software to create cladograms
• helped reclassify some groups of species
• takes time but very useful

Question 11

Falsifying theories

Answer 11

SNAPDRAGON and FOXGLOVES
- The Figwort family was the 8th largest family of angiosperms
-after later examination of the three chloroplast genes resulted in the family being split into 6 clades

Question 12

how to analyse a cladogram

Answer 12

time goes up
- more nodes in between = less closely related