Suggest the advantages of using mitochondrial DNA. (To construct a phylogenetic tree)

There is no recombination in mitochondrial DNA from parent to offspring, hence changes in DNA sequence is solely due to the accumulation of mutations over time, so it can reliably be linked to the molecular clock.

Mitochondrial DNA has a faster mutation rate compared to nuclear DNA, hence it is useful for comparing individuals within a species/closely related species, as it requires discernible differences between DNA of organisms being compared.

Principles of evolution

1. Natural populations have great reproductive potential
2. But numbers remain about constant as many offspring fail to survive
3. Due to environmental factors, competition for resources, predators, other selection pressures, that impose a limit on their number and organisms struggle to survive
4. Individuals within a population show variation for natural selection to act on
5. Variants with a selective advantage/which are best adapted to their environment are more likely to survive and reproduce
6. Producing viable fertile offspring which pass on their favourite traits, thus favourable genotypes accumulate over time, leading to increased allele frequencies of favourable alleles
7. Over many generations, evolutionary changes by natural selection and may form new species if reproductive isolation occurs which is necessary for speciation
8. Include examples which may include: Darwin's finches, giraffes and how they got their long necks, peppered moths

Note: don't neglect points 1-4! 

Reproductive isolation is key to explaining speciation

Suggest why the cytochrome b gene is used to measure changes in DNA sequences in closely related species.

1. Cytochrome b is a homologous gene meaning that it is conserved in all the species being compared 
2. was found in their common ancestor; forms the basis of comparison 
3. Yet there are sufficient differences in the DNA of cytochrome b for scientists to distinguish between closely related species 
4. It is found in the mitochondria and hence do not undergo recombination and any mutation accumulates at a regular rate in the maternal line --> can be used for molecular clock