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 1 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 2 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 3 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 4 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. 4 Phylogeny and Systematics 5 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 6