Download 6.1 Evidence for evolution – Further questions and answers Q1. Bk

6.1 Evidence for evolution – Further questions and answers
Q1.
Bk Ch6 S6.1 FQ1
Study the following table, which illustrates the percentage difference in the nucleotides in the DNA of
humans and other primates.
a
Identify the species most closely related to humans. Identify the most distantly related to humans.
b
Use the information to draw an evolutionary tree that reflects the relationships shown in the table.
Species tested against human DNA
Percentage difference
Human
0.0
Chimpanzee
2.4
Gibbon
5.3
Green monkey
9.5
Capuchin monkey
15.8
A1.
Bk Ch6 S6.1 FA1
a
b
The chimpanzee is most closely related to humans. The Capuchin monkey is the most distantly
related.
Evolutionary tree:
Q2.
Bk Ch6 S6.1 FQ2
Explain why a strain of virus that causes sterility in rabbits is more likely to have long-term
effectiveness compared with viruses that cause illness and death, such as the myxoma virus and
calicivirus.
A2.
Bk Ch6 S6.1 FA2
Viruses such as myxoma and calicivirus have significant short-term results in terms of reducing rabbit
populations; however, as shown with the myxoma virus some rabbits will be resistant to the virus and
when they reproduce they pass on this resistance to their offspring. Eventually more and more rabbits
are born that are resistant and the population of rabbits once again grows to plague proportions. A virus
that causes sterility in rabbits means that there will not be a next generation. When the affected rabbits
die they will have left no offspring. If a large percentage of rabbits can be affected by such a virus,
rabbit numbers will take a dramatic and more permanent decline.
Q3.
Bk Ch6 S6.1 FQ3
Discuss the effectiveness of the myxoma virus and calicivirus in controlling rabbit populations in
Australia. Include
a
the reasons for release of the virus
b
the short-term and long-term effectiveness of the myxoma virus
c
i the short-term effect of calicivirus—gather recent data to quantify your results
6.1 Evidence for evolution FQA
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d
ii the predicted long-term effectiveness of calicivirus (give reasons for your answer here)
potential problems associated with the use of these forms of biological control.
A3.
Bk Ch6 S6.1 FA3
a
b
c
d
Rabbits are a significant pest in Australia that have caused a great deal of ecological and
economic damage. For this reason the myxoma virus was introduced in 1950 to combat the
problem. When rabbit populations had returned to plague proportions by the late 20th century,
calicivirus was introduced in a second attempt to remove rabbits.
Initially the myxoma virus was very effective, responsible for a dramatic decline in the rabbit
population with 99% of affected rabbits dying from the disease. However, over time the
effectiveness of the virus decreased and after 10 years the death rate had dropped to 50%. This
occurred because some rabbits were resistant to the virus and when they reproduced their
offspring were also resistant. Eventually rabbit populations returned to plague proportions.
i Calicivirus has been very effective at reducing rabbit populations throughout Australia.
When it was officially released in 1996 it was responsible for a dramatic decline in rabbit
populations in South Australia with between 80% and 95% effectiveness in the first couple
of months. The virus is still highly successful with a current 90% death rate for infected
rabbits in dry, inland regions; however, the death rate for rabbits in cooler, wetter areas is
lower.
ii It is possible that some rabbits may be resistant to calicivirus. If this is so then we can expect
a repeat of the myxoma virus scenario where resistant rabbits are both unaffected by the
virus and produce resistant offspring. In these circumstances rabbit populations might be
expected to increase again in the long term.
The introduction of biological control agents must be done very carefully. It is critical that viruses
such as myxoma or calicivirus are specific to a particular kind of organism, that is, the disease
does not affect other species of organisms. When this has been established there is still the
potential for mutations to occur in the virus that allow it to cross the species barrier and begin
infecting native animals.
Q4.
Bk Ch6 S6.1 FQ4
Suggest which of the following areas of study provide the most reliable evidence for evolutionary
pathways. Explain why you think so.
palaeontology biogeography
comparative embryology
comparative anatomy biochemistry
A4.
Bk Ch6 S6.1 FA4
Biochemistry would be the most reliable method of drawing accurate conclusions about evolutionary
relationships. Other kinds of analysis can provide information that suggests evolutionary relationships
on the face of the evidence available, but some of these can lead us to the wrong conclusions. For
example, comparative anatomy of some organisms suggests a close evolutionary relationship, but it has
been shown by DNA hybridisation that the organisms are only distantly related.
6.1 Evidence for evolution FQA
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