Question 1
1
The black-legged tick (lxodes scapularis) is an arthropod which sucks blood from humans and other mammals. It is encountered mainly in wooded and semi-wooded areas. Some ticks can be infected by the bacterium Borrelia burgdorferi. When a tick bites a human, the bacterium is often introduced, causing Lyme disease. Lyme disease is a public health problem in North America and, if left untreated, can cause important neurological impairment. The diagram represents the two-year life cycle of a tick.
13 marks
Question 1(a)
1(a)
State the domain into which ticks are classified.
Easystructured1 marks
Answer
eukaryote Accept eukaryotes.
Question 1
1
Analysis of the genome of primates reveals many DNA segments that have been duplicated. It is possible to deduce the stage in evolution at which segmental duplications (SDs) occurred by comparing human and other primate genomes. Human-specific SDs occurred after humans and chimpanzees diverged. Human-chimpanzee shared SDs occurred after the common human-chimpanzee ancestor diverged from gorillas and so on. It is possible to estimate the rates at which SDs occurred during evolution using knowledge of when the primates changed. In the chart the bars indicate numbers of shared SDs and the line shows estimates of the rate of SDs per millions of years (Myr).
0 marks
Question 1(e)
1(e)
Design a cladogram showing the divergence of humans and primates.
Hardshort_answer1 marks
Answer
correct sequence of divergence must be shown (Distance between boundaries is not relevant. Accept straight line diagram or u-shaped cladogram.) eg or
Question D3
D3
Discuss the use of cladograms in phylogenetic studies.
Mediumessay6 marks
Answer
D3. a cladogram is a diagram which shows shared characteristics/phylogenetic relationships; phylogeny is the study of evolutionary origins/ancestry; clade is a group of (all) organisms that evolved from a common ancestor; evidence from biomolecules/DNA/RNA/protein/cytochromes; cladograms can be compared with other representations of phylogenetic relationships/may confirm fossil/anatomical evidence; organisms placed close together in a cladogram are closely related evolutionarily; there may be more than one possible cladogram (for a particular group) raising questions about evolutionary relationships; divisions between clades/nodes suggest the sequence in which groups diverged; cladograms can be used to estimate time since groups diverged; cladograms are often similar to classification based on other evidence/traditional methods; \\ cladograms may lead/have led to reclassification of a group;
Question 3
3
Explain cladistics as a method of classifying organisms.
MediumEssay6 marks
Answer
a. cladistics uses cladograms/tree diagrams; b. show clades/branches (in parallel) that begin at a point/node; c. each clade includes a (common) ancestral organism/node and all its descendents; d. members of a clade share derived/inherited characteristics; e. clades are nested/subsets of larger clades; f. cladograms show evolutionary history/origin of organisms / phylogeny; g. branch length (of clade) can indicate (relative) amount of genetic change/time; h. clades based on (objective) molecular analysis/genetic evidence / differ in amino acid sequences/DNA base changes/mutations; i. fewest number of differences/maximum parsimony determines branch separation; j. predictability of DNA base changes/mutation rates suggests evolutionary timelines; k. problems arise when gene change varies (greatly) from one gene to the next; I. cladograms may not match traditional/Linnaean classification; m. (mismatch) prompts re-examination of data / reclassification of a group; Some of the above points may be included in a correctly annotated diagram clearly stating above points.
Question 3
3
Discuss the use of cladograms in classification and research into the evolutionary origins of living organisms.
MediumEssay6 marks
Answer
a cladogram is (often) a tree-like diagram; nodes/branches represent the splitting of (two) new groups from a common ancestor/ nodes represent common ancestor; members of a clade (above a node) evolved from a common ancestor; members of a clade share a set of features not found in more (accept these marking points on a clearly annotated diagram) distantly related species; classification was traditionally based on morphology; morphology is still important in cladistics for fossil species; cladistics is also based on molecular differences/base sequences/amino acid sequences; cladistics is based on probability/the Principle of Parsimony/Occam's razor; but improbable events do occur, so relationships can be wrong; cladistics allow predictions to be made; but a common ancestor may not have existed/diverging species may hybridize; classification based on cladograms often give the same result as traditional classification; in some groups cladograms have led to revised classification;