5.4 Cladistics

Question 1

What is cladistics?

Answer 1

CLADISTICS - a method of classifying organisms into groups called clades - organised using cladograms (shows evolutionary history)

One separation (speciation) by dichotomous keys - one clade

Question 2

Cladogram anatomy

Answer 2

• root: initial ancestor, common to all in cladogram
• nodes: represent speciation of a species into two species
• outgroup: most dinstantly related species - used for comparison
• clade: a common ancestor and all its descendants

Question 3

Using whaich evidence can cladograms be created?

Answer 3

• structural evidence
• genetics (using softwares to compare the sequences)

Question 4

Explain convenience of molecular evidence for cladograms

Answer 4

• genetic code is universal for all forms of life
• genetic variations accumulate - can be compared between species
• to compare molecular sequences non-coding parts of genomes are used
• protein sequences can also be used - less accurate due to codon degeneracy

Question 5

What is the relationship between the genetic variation and time?

Answer 5

Positive correlation: the longer the time - the more mutations - more diverse genetic make up

Question 6

Explain the concept of molecular clock

Answer 6

Genes mutate at aroun 1bp per 100 thousand years

Limitations:

• different genes/proteins change at different rates
• the rate of change of the same gene may be different in different organisms
• some changes may be reversed mby later changes - years not accounted

Question 7

Explain convenience of structural evidence in cladograms

Answer 7

• easier to group - observation for morphological structures between organisms

Limitations:

• closely related organisms may show different properties due to adaptive radiation
• distantly related organisms may show similar properties due to convergent evolution

Question 8

Homologous vs analogous structures

Answer 8

• Homologous structures - traits that are similar because they are derived from common ancestry
• Analogous structures - traits that are superficially similar but were derived through separate evolutionary pathways

Question 9

Explain convergent evolution

Answer 9

CONVERGENT EVOLUTION: the independent _evolution of similar feature_s in species with distinct lineages

• when different species occupy the same habitat - same selection pressures

Example: evolution of wings in birds, insects, bats

Question 10

Fins vs pentadactyl limb as homologous/analogous structures

Answer 10

Question 11

Role of mtDNA in evolution

Answer 11

mtDNA is only passed on in the maternal line

Benefits over nucleus DNA:

• more direct genetic lineage as mtDNA inherited only form the mothers
• no recombination – maintaining sequence accuracy
• higher mutation rate – mitochondria produce reactive oxygen specie - sequences mutate at higher rate
• high copy number –many mitovhondira - large amounts of mtDNA gathered for sequencing