Cladistics

Question 1

What is a clade?

Answer 1

• A group of organisms that have evolved from a common ancestor
• Members in a clade will possess common characteristics

Question 2

What are Cladograms?

Answer 2

• Branched tree diagrams to show evolutionary relationships
• Each branch represents a speciation event splitting of two new groups from a common ancestor
• Show most probable sequence of divergence, demonstrate likely evolutionary history
• The fewer the no. of nodes between two groups, closer they are related

Question 3

What are the key features of a cladogram?

Answer 3

• Root: initial ancestor, common to all organisms
• Nodes: corresponds to a hypothetical common ancestor of two species (fork)
• Outgroup: Most distantly related species
• Clades: all branches connected to a node

Question 4

What is molecular evidence?

Answer 4

• Shows how long ago the mutations occurred that caused speciation
• Closer related organisms have mutations that occurred at the same time
• The molecular heritage is discovered in the DNA looking at base and amino acid sequences
• The more similar the sequences are, closer related

Question 5

What is the molecular clock?

Answer 5

• Technique that uses mutation rate to deduce the time when two or more life forms diverged (speciation)

Question 6

How are molecular clocks identified?

Answer 6

• If genes, undergo mutations at a constant rate, the rate of change is used to calculate the time of divergence (occured)

Question 7

What do molecular clocks show?

Answer 7

• Indicate how much time has passed since two species diverged from their common ancestor
• Many differences in DNA, more mutations (takes longer), species not closely related

Question 8

What type of correlation is there?

Answer 8

• A positive correlation between the no. of differences between two species and the time since they diverged from a common ancestor
• Because sequence differences accumulate gradually
• The longer ago the species separated, the more differences there are in the DNA

Question 9

What type of DNA is used for molecular evidence and why?

Answer 9

• Use non-coding DNA sequences, provide the most information because they are highly repetitive, mutations will occur more frequently in these sections of DNA

Question 10

Why are coding sequences and amino acid sequences not used?

Answer 10

• Mutations in these sections occur at a much slower rate

Question 11

What is convergent evolution?

Answer 11

• Independent evolution of similar features in species with distinct lineages
• Creates analogous structures
• Occurs when different species occupy the same habitat, exposed to same pressures
• Shared conditions, common adaptations, structural similarity

Question 12

What is divergent evolution?

Answer 12

• Groups from the same common ancestor evolve and accumulate differences, speciation, may still share characteristics
• Response to abiotic factors (environmental conditions) or biotic factors (competition)

Question 13

What are analogous traits?

Answer 13

• Structures that have similar functions but have evolved separately through convergent evolution, different ancestors

Question 14

What are homologous traits?

Answer 14

• Structures that are similar because of shared ancestry, may have different functions, divergent evolution

Question 15

How was the figwort family reclassified?

Answer 15

• Figworts were the 8th largest family of flowering plants (angiosperms), 275 genera
• The figwort plants were not similar enough in structure to function as a group
• Chloroplast gene examined, split the family into 5 different clades
• Now 36th largest family, less than half remained in the family