Question 1
Paper 1A style
Which is the correct way to write the binomial of the grey wolf?
- Canis Lupus
- canis lupus
- Canis lupus
- Lupus canis
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Answer: C – genus first with a capital letter, species name lowercase, in italics [1]
Question 2
Paper 1A style
Which statement about chromosome numbers is correct?
- All mammals have 46 chromosomes in their body cells.
- Diploid cells have an even number of chromosomes.
- Species with more chromosomes are more complex.
- Chimpanzees have fewer chromosomes than humans.
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Answer: B – chromosomes in diploid cells are in homologous pairs [1]
Question 3
Paper 1A style
What is the main source of genome diversity between individuals of the same species?
- Differences in the number of genes
- Single-nucleotide polymorphisms
- Differences in chromosome number
- Differences in the genetic code
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Answer: B – members of a species share most of their genome; SNPs give some diversity [1]
Question 4
Paper 2A style
(a) State the biological species concept. [1] (b) Outline why it can be an arbitrary decision whether two populations are the same species or different species. [3]
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- (a) a group of organisms that can breed and produce fertile offspring [1]
- (b) speciation is the splitting of one species into two or more [1]
- (b) speciation usually happens gradually / not by a single act [1]
- (b) non-interbreeding populations diverge / become more and more different in their traits [1]
- (b) no clear point at which they become separate species / intermediate stages exist [1]
- (b) interbreeding cannot be tested if populations are geographically separated OWTTE [1]
- max 4
Question 5
Paper 2A style
Humans have 46 chromosomes and chimpanzees have 48. Evaluate the evidence for the hypothesis that human chromosome 2 arose from the fusion of two chromosomes found in a shared primate ancestor.
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- banding pattern of human chromosome 2 matches chimpanzee chromosomes 12 and 13 (2A and 2B) end to end [1]
- telomere sequences found near the middle of chromosome 2 / at the fusion point [1]
- remains of a second (inactive) centromere on chromosome 2 [1]
- gene order (largely) matches that on the two chimpanzee chromosomes [1]
- fusion explains reduction from 48 to 46 / 24 to 23 pairs [1]
- the hypothesis is testable / made predictions that could have been falsified [1]
- evidence supports but does not prove the hypothesis / fusion itself was not observed OWTTE [1]
- max 4
Question 6
Paper 1B style
The table shows approximate haploid genome sizes taken from a genome database. (a) Calculate how many times larger the genome of Paris japonica is than the human genome. [1] (b) Using the data, evaluate the hypothesis that genome size increases with the complexity of an organism. [3] (c) Suggest one reason why some plants have much larger genomes than humans. [1]
| Organism | Group | Genome size / million base pairs |
|---|---|---|
| Escherichia coli | bacterium | 4.6 |
| Saccharomyces cerevisiae | fungus (yeast) | 12 |
| Drosophila melanogaster | insect | 180 |
| Arabidopsis thaliana | flowering plant | 135 |
| Homo sapiens | mammal | 3,100 |
| Triticum aestivum | flowering plant | 16,000 |
| Paris japonica | flowering plant | 149,000 |
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- (a) 149,000 ÷ 3,100 = 48 (times) [1] Accept 48.1
- (b) supported: simplest organisms / bacterium and yeast have the smallest genomes [1]
- (b) not supported: plants such as wheat / Paris japonica have larger genomes than humans [1]
- (b) Arabidopsis and Drosophila have genomes of a similar size / same order of magnitude despite being very different organisms OWTTE [1]
- (b) conclusion: no close correlation between genome size and complexity / hypothesis not supported overall [1]
- (b) only one or a few species per group / small sample of species [1]
- (c) more non-coding / repetitive DNA [1] Accept extra copies of whole chromosome sets / polyploidy
- max 5
Question 7
Paper 2A style
Outline current and potential future uses of whole genome sequencing.
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- sequencing is increasingly fast and cheap, so many genomes can be compared [1]
- current: research into evolutionary relationships between species / comparing numbers of base differences [1]
- current: finding SNPs / variation linked to traits or diseases [1]
- future: personalised medicine [1]
- choosing drugs / doses / predicting disease risk from an individual's genome [1]
- max 3