Phylogeny and Systematics
1.
(a)
(b)
a group of related organisms sharing a common ancestor / a
group of organisms containing an ancestor and all of its
descendants / OWTTE
1
homologous structures evolved from a common ancestor while
analogous structures did not;
example of homologous and example of analogous; (both needed)
2
e.g. an example of homologous is pentadactyl limb in mammals
and birds / mouth parts in house fly and mosquito/other valid
example and an example of analogous is eye in vertebrates and
squid/octopus / wings of insect and bat / jointed legs of vertebrates
and insects/other valid example
(c)
Two correct labels for [1].
2 max
(d)
opposable thumbs (enable grabbing);
flat fingernails (instead of claws/for scratching);
forward-facing eyes for stereoscopic vision;
rotatable shoulder joints (for tree-climbing adaptation);
skull modified for upright posture;
large brain to body/skull ratio enables higher levels of thinking;
2 max
[7]
2.
(a)
(b)
self-replicating and catalytic activities of RNA;
short sequences of RNA have been able to duplicate/copy other RNA
molecules accurately;
RNA enzyme/ribozyme (able to synthesize other molecules);
3-dimensional structure of ribosome catalytic sites (for peptide formation)
are composed of RNA;
able to store information in sequence of (4) nucleotides (similar to DNA);
2 max
all living organisms use DNA as genetic/hereditary material;
genetic code is (almost) universal;
idea that mutations accumulate gradually in DNA;
2 max
Phylogeny and Systematics
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Phylogeny and Systematics
(c)
(d)
A is most similar to B;
A is equally similar to C and D;
A is least similar to both C and D;
2 max
methods used to prepare cladograms use a different approach from
traditional classification/taxonomy;
show ancestral relationships;
reflect how recently two groups shared a common ancestry;
cladograms are (objective/accurate because they are usually) based
on molecular differences;
they should be considered as a good complement to traditional
classification;
2 max
[8]
3.
DNA/genetic code is universal;
same four bases adenine, cytosine, guanine and thymine;
To award the mark full

names of all four are required.
always pairing of AT and GC;
same structure of double helix of complementary strands;
use the same 20 amino acids in their proteins;
all left-handed;
same/similar enzymes in processes of replication/transcription/translation;
small differences in DNA/proteins show closer relationships;
e.g. hemoglobin/cytochrome C/gene structures show relationships among
organisms;
humans have the same biochemistry as all organisms so part of same
evolution/common ancestry;
mitochondrial DNA used to determine maternal lines / y chromosome used
to determine paternal lines;
endosymbiotic theory/mitochondria/chloroplast structures indicate common
lines of evolution;
6 max
[6]
4.
(a)
11
1
(b)
Ile and Glu (both needed to award the mark)
1
(c)
share 17 (out of 29) amino acids in common / more amino acids
similar than different;
both have Mn in the enzyme (as cofactor);
greatest difference between them is from amino acid 18 to 22;
mitochondrial has Gly (position 12) while E. coli (Mn) never has Gly;
Leu is most common amino acid in both appearing four times / other
valid comparison;
2 max
Phylogeny and Systematics
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Phylogeny and Systematics
(d)
(e)
divergent (evolution) as the cytoplasmic dismutase shows a greater
number of differences (than the other three enzymes);
divergent as convergent (evolution) implies existence of analogous
structures and there are none here;
1 max
endosymbiotic theory states bacteria were engulfed by organisms to
become mitochondria;
sequence comparison between mitochondrial and bacterial dismutase
supports this hypothesis;
more similarity in the amino acid sequence between mitochondrial
and bacterial dismutase than between mitochondrial and cytoplasmic
dismutase;
2 max
[7]
5.
(a)
allele frequency: measurement of how often an allele appears (i.e. A or a);
gene pool: total sum of all the genetic information available for reproduction
within the population;
Both responses are needed to award the mark.
1 max
(b)
large population;
random mating;
no migration / immigration / emigration;
no mutations;
no natural selection;
(c)
1 max
phylogeny is the evolutionary line of descent;
(e.g. mitochondrialDNA /
the study of similar molecules in two different species; 
hemoglobin / Cytochrome c)
the greater the differences, the longer the time span since the two species
had a common ancestor;
variation can be due to mutations;
mutations are chance events so caution must be taken when interpreting
these;
3 max
(d)
organization of data helps to identify organisms;
suggests evolutionary links;
suggests the closeness of a relationship the more similar the
characteristics are;
allows prediction of characteristics shared by members of a group;
2 max
[7]
Phylogeny and Systematics
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Phylogeny and Systematics
6.
(a)
(b)
speciation is the formation of a new species by the splitting of an
existing species;
allopatric speciation caused by geographical separation;
sympatric speciation occurring within the same habitat caused
by different niches / caused by courtship/feeding differences/
behavioural differences;
both processes lead to isolation of sub-populations;
isolation favours certain genetic variations (within a species);
over time this leads to genetic barriers/speciation;
Both allopatric and sympatric speciation must be mentioned. [3 max]
if only one mentioned.
4 max
all organisms have DNA as the genetic material;
all organisms use (approx.) 20 different (L) amino acids;
genetic code is (nearly) universal;
mechanism for protein synthesis is similar;
metabolic pathways are similar;
if parts of DNA (genes) are shared between organisms then it
denotes (close) relationship;
the greater the percentage of genes shared, the closer the genetic
relationship;
mitochondrial DNA is maternally inherited in most organisms/
phospolipid membranes/ATP common in most (all) organisms;
conserved genes have similar function;
6 max
[10]
7.
(a)
2 (%) (units not required)
Allow answers in the range of 2.0 to 2.1.
1
(b)
17.5% (allow answers in the range of 17.3 to 17.7%)
1
(c)
both show range variation;
average genetic divergence of mtDNA much less  Allow numerical

than average nDNA;
comparison.
greater range of genetic variation in nDNA than mtDNA / 18% in nDNA
and 6.5% in mtDNA;
three of mtDNA have less than 1% genetic divergence while none of
nDNA have less than 5%;
the highest divergence of mtDNA is similar to the lowest of nDNA;
mtDNA3 and nDNA8 have no (known) species with the same sequence
divergence;
3 max
Phylogeny and Systematics
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Phylogeny and Systematics
(d)
mtDNA (appears to be) more stable (due to less genetic divergence) /
converse;
mtDNA (likely) has fewer genes which could be a limit on the
accumulation of mutations / converse;
mtDNA more stable as no meiosis/cross-over/chromosome
re-assortment;
smaller range of genetic divergence may indicate that they
had a common ancestor/are more closely related;
natural selection could put more pressure on nDNA / more
evolutionary change;
problem in using mutations as an evolutionary clock / different
genetic divergence / different rates of mutation depending on the
genes examined;
the high rates of nDNA6 divergence could be neutral substitutions /
no effect / intronic;
insufficient data to know the effects of these mutations;
3 max
[8]
8.
(a)
analogous: [2 max]
similar structures but different (evolutionary) origins / different basic
structure but same function;
e.g. vertebrate and invertebrate eyes / insect and human legs;
Accept any other valid example.
homologous: [2 max]
structures are of similar origin / same basic structure but different functions;
e.g. pentadactyl limbs in vertebrates;
Accept any other valid example.
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Phylogeny and Systematics
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Phylogeny and Systematics
(b)
 Accept examples
for two alleles of a given genetic characteristic, three 
of genotypes.
possible genotypes exist;
predicts frequencies of dominant and recessive alleles of a given gene;
homozygous for each allele and heterozygous;
frequency of dominant allele = p, recessive/albino allele = q;
total frequency of both alleles = 1 or p + q = 1;
random mating, probability of receiving two dominant alleles is p × p or p2;
probability of receiving two recessive alleles is q ×q or q2;
expected frequency of heterozygous genotype is 2pq;
p2 + 2pq + q2 = 1;
assumes no mutations / large population / random mating / no selective
pressure / no immigration nor emigration;
explains why recessive alleles do not disappear over several generations;
1
q2 =
or q = 0.007 (frequency of recessive);
20 000
p = 1 – 0.007 or 0.993;
frequency of dominant p2 = 0.986 or 98.6%;
frequency of heterozygotes 2pq = 0.014 or 1.4%;
Accept values with more significant figures.
5 max
[9]
9.
DNA/RNA found in all living organisms/genetic code is universal;
amino acids all L- not D- isomers
same 20 amino acids/proteins found in all living organisms;
involves comparing similarities and differences in the amino acid sequence of the
same molecule;
e.g. hemoglobin;
involves comparing base sequences of variable regions of DNA;
e.g. mitochondrial DNA;
the more similar the base/amino acid sequence, the more closely related;
comparing amino acid sequences that result in the phenotype/comparing DNA
sequences that result in the genotype;
evidence for molecular evolution in drug resistance;
6 max
[6]
Phylogeny and Systematics
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