1. 1
   Salamanders of the genus Ensatina live in the mountains that form a ring around the Central Valley of California. Populations change gradually in colour pattern around the ring, and neighbouring populations interbreed where they meet. At the southern end of the ring, where the two ends of the chain meet, a plain-coloured form and a blotched form live in the same forests but rarely interbreed. All the populations are currently classified as one species, Ensatina eschscholtzii.

   (a)

   Which is the correct way to write the binomial name of these salamanders in a report?

   [1 mark]

   • Aensatina Eschscholtzii
   • BEnsatina Eschscholtzii
   • CEnsatina eschscholtzii
   • DENSATINA eschscholtzii

   (b)

   What does the first part of the name, Ensatina, identify?

   [1 mark]

   • AThe species
   • BThe subspecies
   • CThe family
   • DThe genus

   (c)

   Explain why it is difficult to decide whether the two forms at the southern end of the ring are the same species.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Humans have 46 chromosomes in their body cells and chimpanzees have 48. The banding pattern of human chromosome 2 matches, end to end, the banding patterns of two separate chromosomes of the chimpanzee (numbered 12 and 13 in older studies). DNA sequencing shows repeated telomere sequences, normally found only at the ends of chromosomes, near the middle of human chromosome 2, and a second, inactive centromere at a position matching the centromere of one of the chimpanzee chromosomes.

   (a)

   How many chromosomes are present in a chimpanzee sperm cell?

   [1 mark]

   • A24
   • B23
   • C46
   • D48

   (b)

   Which statement is a testable hypothesis?

   [1 mark]

   • AHuman chromosome 2 formed so that humans could become more intelligent
   • BHuman chromosome 2 arose by the fusion of two chromosomes present in an ancestor shared with chimpanzees
   • CEvery species has the number of chromosomes it was meant to have
   • DChromosome number is the most important difference between humans and apes

   (c)

   Outline how chromosomes are arranged when a karyogram is prepared.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student extracts information on genome size from an online database. Genome size is given in millions of base pairs (Mbp): the bacterium Escherichia coli 4.6 Mbp with about 4300 genes; baker's yeast 12 Mbp with about 6000 genes; the flowering plant Arabidopsis thaliana 135 Mbp with about 27 000 genes; humans 3100 Mbp with about 20 000 protein-coding genes; the marbled lungfish about 130 000 Mbp; and the flowering plant Paris japonica about 149 000 Mbp.

   (a)

   Calculate how many times larger the genome of the marbled lungfish is than the human genome, and state what this suggests about the relationship between genome size and complexity.

   [3 marks]

   (b)

   Evaluate, using the data, the claim that the number of genes in an organism indicates its complexity.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The first human genome sequence was completed by the Human Genome Project, which took 13 years (1990–2003) and cost about US$2.7 billion. By the 2020s a whole human genome could be sequenced in about one day for under US$1000. Comparisons of many genomes show that any two unrelated humans differ at roughly 1 in every 1000 base positions, mostly as single-nucleotide polymorphisms (SNPs). Humans and chimpanzees differ at about 1.2% of base positions in the parts of their genomes that can be aligned.

   (a)

   Using the data, explain the unity and diversity of genomes within and between species.

   [6 marks]

   (b)

   Discuss current and potential future uses of whole genome sequencing, referring to the changes in its speed and cost.

   [6 marks]

   Total for question 4: 12 marks

End of questions