Describing Evolution
Match the key terms in the list below to the definition in the box.
Key term
Definition
Evolutionary relationships that exist between individuals or groups of
organisms
Small scale variation of allele frequencies within a species or population,
in which the descendant is of the same taxonomic group as the ancestor
an increase in taxonomic diversity or morphological disparity over time
Variation of allele frequencies at or above the level of species over
geological time, resulting in the divergence of taxonomic groups, in
which the descendant in a different taxonomic group to the ancestor
Both mitochondrial DNA and chloroplast DNA have been useful in the determination of relationships between
related organisms. The data in Table 1 shows that differences in the mitochondrial DNA nucleotide sequences
between pairs of vertebrates.
Table 1. Comparison of percentage differences in DNA nucleotide sequences between pairs of vertebrates.
Groups Compared
Human - chimpanzee
Human – gibbon
Human – rhesus monkey
Human – African galago
House mouse – Norwegian rat
Cow – sheep
Cow - pig
Difference in DNA sequences
1.6%
3.5%
5.5%
28.0%
20.0%
7.5%
20.0%
Questions
1. What does the degree of similarity of the nucleotide sequences of living things tell us about their
relationships?
2. Compare the similarity of the genomes of the cow and sheep with that of the cow and the pig. What can you
conclude from this?
3. Relate the results in Table 1 to the concept of macroevolution.
Case Study: the evolution of the marsupials
Marsupials are a type of mammal that carry their young in a pouch. They are found only in Australasia and South America and
include kangaroos, koalas, wombats, possums and opossums. DNA evidence supports a South American origin for marsupials,
with Australian marsupials arising from a single Gondwanan migration of marsupials from South America to Australia, via
Antarctica.
The evolutionary relationships among the seven marsupial orders – four Australasian and three South American – have not yet
been resolved. The two recently sequenced marsupial genomes of the South American opossum and the Australian tammar
wallaby, provided scientists with an opportunity to apply a completely new approach to resolve marsupial relationships.
The exhaustive computational and experimental evidence provided important insight into their evolution and resolved most
branches of the marsupial evolutionary tree. The results of this study are shown in Figure 1.
Nilsson MA et al. (2010) Tracking Marsupial Evolution Using Archaic Genomic Retroposon Insertions. PLoS Biol 8(7):e1000436.
Figure 1. Diagram showing evolutionary relationships between the marsupials. The first marsupials arose in South America, and
then migrated to Australia via Antarctica.
Questions
1. Would the type of evolution shown in Figure 1. be an example of microevolution? Give reasons for your
answer.
2. Describe the purpose of a phylogenetic tree.
3. State the factor that is represented by moving from left to right across the diagram.
4. Using an example from Figure 1, explain the significance of forks in the diagram.
5. Explain why this study could be called comparative genomics.