8 - Selection and speciation

Question 1

EXAM QUESTION

The population of trees in the forest evolved adaptations to the mountain environment.
Use your knowledge of selection to explain how. (3)

Answer 1

1. Variation in original colonisers
/ mutations took place;
2. Some better (adapted for)
survival (in mountains);
3. Greater reproductive success;
4. Allele frequencies change;

Question 2

EXAM QUESTION

Several years later, scientists repeated their study on this population. They found that
the frequency of the recessive allele had decreased.
What type of natural selection appears to have occurred in this population of sea otters? Explain how this type of selection led to a decrease in the frequency of the recessive allele. (2)

Type of selection?
Explanation?

Answer 2

1. Directional;
2. The recessive allele confers disadvantage/ the dominant
   allele confers advantage/more likely to survive / reproduce;

Question 3

EXAM QUESTION

On islands in the Caribbean, there are almost 150 species of lizards belonging to the
genus Anolis. Scientists believe that these species evolved from two species found on
mainland USA. Explain how the Caribbean species could have evolved. (6)

Answer 3

1. Geographic(al) isolation;
2. Separate gene pools / no
   interbreeding/gene flow (between
   populations);
3. Variation due to mutation;
4. Different selection pressures /
   different abiotic/biotic conditions/
   environments/habitats;
5. Different(ial) reproductive success /
   selected organisms (survive and)
   reproduce;
6. Leads to change/increase in allele
   frequency;

Question 4

EXAM QUESTION

The Amazonian forest today contains a very high diversity of bird species.
l Over the last 2 000 000 years, long periods of dry climate caused this forest to
separate into a number of smaller forests.
l Different plant communities developed in each of these smaller forests.
l Each time the climate became wetter again, the smaller forests grew in size and
merged to reform the Amazonian forest.
6 (a) Use the information provided to explain how a very high diversity of bird species has
developed in the Amazonian forest. (5)

Answer 4

1. No interbreeding / gene pools are
separate / geographic(al)
isolation;
2. Mutation;
3. Different selection pressures /
different foods/niches/habitats;
4. Adapted organisms survive and
breed / differential reproductive
success;
5. Change/increase in allele
frequency/frequencies;

Question 5

EXAM QUESTION

Speciation is far less frequent in the reformed Amazonian forest. Suggest one reason for this. (1)

Answer 5

Similar/same environmental/abiotic/biotic
factors / similar/same selection pressures
/ no isolation / gene flow can occur
(within a species);

Question 6

What type of natural selection is shown in the graph? (1)

Describe the evidence for your answer. (1)

Answer 6

Stabilising;

Few geese survive at the extremes/most survive from the middle of the range;

Question 7

Selection process (5)

Answer 7

Variation in original colonisers / mutations took place
Some individuals possess alleles that make them better adapted for survival
Greater reproductive success
Pass on favourable alleles to next generation
Allele frequencies change

Question 8

Directional selection (5)

Answer 8

Environment changes
Individuals at one extreme possess alleles that make them better adapted for survival/confer advantage
Greater reproductive success
Pass on favourable alleles to next generation
Other extreme eliminated

Question 9

Stabilising selection (5)

Answer 9

Environment stable
Average individuals possess alleles that make them better adapted for survival/confer advantage
Greater reproductive success
Pass on favourable alleles to next generation
Both extremes eliminated

Question 10

Speciation (6)

Answer 10

1. Geographical isolation
2. Separate gene pools / no interbreeding
3. Variation due to mutation
4. Different selection pressures
5. Different reproductive success
6. Leads to change in allele frequency

Question 11

Define speciation

Answer 11

Speciation = the evolution of two or more species from existing species.