5.4

Question 1

what is included in a class

Answer 1

• all species that are alive today (descended from the same common ancestor)
• the common ancestral species (may or may not be alive today)
• all species which have evolved from the same common ancestor which has gone extinct

Question 2

in cladograms what does a branch represent

Answer 2

each branch represents a species

Question 3

in cladograms what does a node represent

Answer 3

each node represents a speciation event

Question 4

in cladograms what does the root represent

Answer 4

the common ancestral species of all the organisms in the cladograms

Question 5

What’s the correlation between number of nodes and relatedness

Answer 5

the more nodes the more distantly related

the less nodes the more closely related

Question 6

explain why cladograms may not be reliable

Answer 6

adaptive radiation:
a populations of the same common ancestor spreads to different environment with different selection pressures they adapt to their environment in different ways (homologous)

convergent evolution:
when distantly related organisms have very similar features due to similar selections pressures even though they’ve evolved independently from different ancestors (analogous)

Question 7

compare analogous and homologous traits

Answer 7

Question 8

what evidence is used nowadays to decide which species are part of a clade

Answer 8

• DNA base sequences (coding & non-coding)
• RNA base sequences
• amino acid sequences of proteins (reliable due to universal genetic code)

Question 9

what does comparing DNA base sequences show and how does it achieve this

Answer 9

shows evolutionary divergence

• over the course of millions of years mutations accumulate within given sections of DNA
• the number of differences between comparable DNA base sequences can demonstrate evolutionary divergence between species
• the more similarities the more closely related and vice versa

Question 10

what provides the best means of comparison between species and why

Answer 10

non-coding DNA

• mutations accumulate more readily in non-coding DNA as they often have neutral effect
• gene sequences accumulate mutations at a slower rate as changes may affect protein structure and function
• non-coding DNA is typically used to compare closely related species & gene sequences are used to compare distantly related species

Question 11

when is it appropriate to use amino acids to compare species

Answer 11

• amino acid sequences change very slowly and are typically used to compare very distantly related species (eg. in different taxa)

Question 12

what is the original cause of differences in base sequences of DNA between individuals

Answer 12

mutations

Question 13

how are mutations used as a molecular clock

Answer 13

• same genes or amino acids may accumulate mutations at a relatively constant rate
• if this rate is reliable scientists can calculate the time of divergence of a species according to the number of differences

Question 14

what factors limit the concept of the molecular clock

Answer 14

• molecular clocks assume that mutation rate is constant - may actually vary over time
• different genes or proteins may also change at different rates from each other
• rates of changes may vary between different groups of organisms (particularly if generation times are different)
• over long periods of time previous changes may be reversed