17.11 End of Chapter Questions

1. Which of the following gives rise to genetic variation in a population? [1]
1 crossing over and independent assortment in meiosis
2 diff erent environmental conditions
3 random mating and fertilisation
4 mutation

A 1, 2, 3 and 4
B 1, 2 and 3 only
C 1, 3 and 4 only
D 2, 3 and 4 only

2. A species of finch living on an isolated island shows variation in beak size. Birds with larger beaks can eat larger seeds.
Aft er a period of drought on the island, large seeds were more plentiful than small seeds and the average size of the finches’ beaks increased.
What explains this increase in size of beak? [1]

A artificial selection acting against finches with small beaks
B directional selection acting against finches with small beaks
C increased rate of mutation resulting in finches with larger beaks
D stabilising selection acting against finches with the smallest and largest beaks

3. Which eff ect of natural selection is likely to lead to speciation?

A Diff erences between populations are increased.
B The range of genetic variation is reduced.
C The range of phenotypic variation is reduced.
D Favourable alleles are maintained in the population. [1]

There are three genotypes of the gene for the β-globin polypeptide: Hb^AHb^A, Hb^AHb^S and Hb^SHb^S.
Copy and complete the table to show which genotypes have a selective advantage or disadvantage in different regions of the world. [4]

The wings of butterflies are covered with microscopic scales that give them their colour and also provide waterproofing.
The wings of some species have large transparent areas through which the colour of the vegetation on which the butterfly has settled can be seen. Because they lack scales, these areas have poor waterproofing.
The butterflies are eaten by birds.

a. Describe two selection pressures that are likely to control the size of the transparent areas of the wings of these butterflies. [2]

b. In what circumstances might there be selection for larger transparent areas in the wings? [1]

Rearrange the order of the following statements to give a flow diagram showing the evolution of resistance to the antibiotic streptomycin by the bacterium Escherichia coli. [3]

1 Most of the population of E. coli is resistant to streptomycin.
2 A mutation in a DNA triplet of a plasmid, changing TTT to TTG, gives an E. coli bacterium resistance to streptomycin.
3 The resistant bacterium divides and passes copies of the R plasmid (plasmid with gene for resistance to antibiotic) to its off spring.
4 Sensitive bacteria die in the presence of streptomycin as a selective agent.
5 The frequency of the mutated gene in the population increases.
6 The resistant bacterium has a selective advantage and survives.

Hybrids produced by crossing two different inbred (homozygous) varieties are often more vigorous in their growth than either of their parents. Copy and complete the flow diagram to show how breeders of maize produce plants that show hybrid vigour. [6]

Copy and complete the table to compare artificial selection with natural selection. [3]

Pale and dark peppered moths were collected and placed on pale and dark areas of bark on trees in a park in Liverpool, England.

Some of the moths were predated by birds. The results of the investigation are shown in the table.

a. 40 dark moths were placed on dark bark. Calculate the number of moths taken by birds. Show your working. [2]

b. Suggest an explanation for the diff erences in the numbers of moths taken by birds. [4]

The snail Cepaea nemoralis may have a yellow, pink or brown shell. Each colour shell may have up to five dark bands, or have no bands. Both shell colour and number of bands are genetically controlled. The snails are eaten by birds such as thrushes, which hunt by sight.
The following observations were made:
• Most snails living on a uniform background, such as short grass, have no bands.
• Most snails living on a green background, such as grass, are yellow.
• Most snails living on a non-uniform background, such as rough vegetation, have bands.

a. Suggest an explanation for these observations. [4]

b. Predict the phenotype of snails living on a dark background of dead leaves. [2]

c. Suggest what will happen, during the course of a year, to the frequencies of the different alleles controlling shell colour and banding in a snail population living in deciduous woodland. (Deciduous trees shed their leaves in autumn. The background for the snails will be made up of dead leaves in the autumn and winter, and green vegetation in the spring and summer.) [4]

The heliconid butterflies of South America have brightly coloured patterns on their wings. A hybrid between two species, Heliconius cydno and H. melpomene, has wing patterns that are diff erent from both parental species.
An investigation was carried out to see whether the hybrid was a new species.
Separate groups of four butterflies, each consisting of a male and female of one of the parental species and a male and female of the hybrid, were placed together and their choices of mates recorded. The results are shown in the table.

a. With reference to the information in the table, explain whether or not the results of the investigation suggest that the hybrid butterfly is a separate species. [4]

b. Suggest how the hybrid could be reproductively isolated from the two parent species of butterfly. [2]

c. Briefly describe how allopatric speciation can occur. [4]