5.4 Cladistics

Question 1

what is cladistics?

Answer 1

method of classifying organisms into clades

Question 2

what does each clade consist of?

Answer 2

• ancestral organism and all of its evolutionary descendants
• members of a class will posses common characteristics as a result of their shared evolutionary lineage

Question 3

what does each branch point represent on a cladogram?

Answer 3

each branch point (node) represents a speciation event by which distinct species are formed via divergent evolution

Question 4

what do cladograms show?

Answer 4

the probable sequence of divergence and demonstrate the likely evilutionary history (phylogeny) of a clade (fewer number of nodes the more closely related 2 groups are expected to be)

Question 5

why does having all organisms which use DNA and RNA as genetic material and the genetic code help to relate people?

Answer 5

• the shared molecular heritage means that base and amino acid sequences can be compared to ascertain levels relatedness

Question 6

why does having all organisms which use DNA and RNA as genetic material and the genetic code help to relate people?

Answer 6

• the shared molecular heritage means that base and amino acid sequences can be compared to ascertain levels of relatedness

Question 7

how can DNA determine the relatedness of organisms?

Answer 7

• the number of differences between comparable base sequences demonstrates the degree of evolutionary divergence
• treated number differences between comparable base sequences suggest more time has passed since 2 species diverged
• a greater number of differences between comparable base sequence suggests more time has passed since 2 species diverged
• the more similar the base sequences of 2 species are the more closely related the 2 species are expected to be

Question 8

How and what do scientists use non-coding DNA sequences? (3)

Answer 8

• non-coding DNA provides the best means of comparison as mutations will occur more readily in these sequences
• gene sequences mutate at a slower rate, as changes to base sequence may potentially affect protein structure and function
• amino acid sequences may also be used for comparison but will have the slowest rate if change due to codon degeneracy

Question 9

what are amino acid sequences typically used to compare?

Answer 9

distantly related species

Question 10

what is DNA or RNA base sequences often used to compare?

Answer 10

closely related organisms

Question 11

what can you calculate is genes and proteins accumulate mutations at a relatively constant rate?

Answer 11

if the rate of change is reliable, scientists can calculate the time of divergence according to the number of differences

Question 12

what is the process of the reliable change in rate to calculate the time of divergence called?

Answer 12

molecular clock

Question 13

what factors is the molecular clock limited by?

Answer 13

• 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, mixing up the accuracy of predictions

Question 14

what are 2 limitations fpoe using morphological differences as a basis for classification?

Answer 14

• closely related organisms can exhibit very different structural features due to adaptive radiation
• distantly related organisms can display very similar structural features doe to convergent evolution

Question 15

what is convergent evolution?

Answer 15

the independent evolution of similar featues in species with distinct lineages

Question 16

why may convergent evolution occur?

Answer 16

when different species occupy the same habitat and are subject to the same selection pressures
- the shared conditions cause common adaptations to be selected in different species
(eg wings of bats, birds and insects)

Question 17

what are traits which are similar because they are derived from common ancestry called?

Answer 17

homologous structures

Question 18

what are traits that are superficially similar but derive through separate evolutionary pathways called?

Answer 18

analogous structures

Question 19

what are 2 examples of species which were reclassified based on molecular evidence?

Answer 19

• crocodiles are more closely related to birds than lizards (although they resemble lizards)
• figwort

Question 20

why was is problematic that the figwort family were classed together?

Answer 20

they were too dissimilar in structure to function as a meaningful group

Question 21

how did scientists examine which made them split the figwort species into 5 different clades?

Answer 21

chloroplast gene