5.4 Cladistics

Question 1

What is a clade?

Answer 1

A clade is a group of organisms that includes a common ancestor and all its lineal descendants. It represents a single ‘branch’ on the ‘tree of life’

Question 2

How is evidence for which species are part of a clade obtained?

Answer 2

Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein

Question 3

What are analogous and homologous traits?

Answer 3

Analogous traits evolve separately but have similar functions, often as a result of convergent evolution. Homologous traits are characteristics shared by organisms due to their common ancestry, indicating divergent evolution

Question 4

Explain the correlation between sequence differences and divergence time.

Answer 4

There is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. More differences in DNA base sequences suggest a longer time since divergence, as mutations accumulate gradually

Question 5

What are cladograms?

Answer 5

Cladograms are tree diagrams that represent the most probable sequence of divergence within clades, based mostly on DNA or amino acid sequence analysis​

Question 6

How can cladograms be used to interpret evolutionary relationships between humans and other primates?

Answer 6

By analyzing the sequence of divergences and the number of nodes between species, cladograms can show how closely related humans are to other primates, with fewer nodes indicating closer relationships

Question 7

What does analysis of cladograms reveal about evolutionary relationships?

Answer 7

Analysis of cladograms can deduce evolutionary relationships, estimate when species diverged, and when their common ancestor existed, based on molecular differences and comparison with fossil records

Question 8

How has evidence from cladistics shown errors in previous classifications based on structure?

Answer 8

Cladistics, using DNA base sequences and protein structures, has shown that previous classifications based on morphological similarities often did not correspond with the evolutionary origins of a group or species​

Question 9

Describe the reclassification of the figwort family using evidence from cladistics.

Answer 9

The figwort family was reclassified into five distinct clades after DNA sequence analysis revealed that the previously thought single clade was actually multiple, showing the importance of molecular evidence in classification​