Practise variation, natural and artificial selection, Hardy–Weinberg calculations, changing allele frequencies, speciation and DNA evidence for evolutionary relationships.
Within a population, the variation for one characteristic is usually the result of genetic and environmental causes.
Both genetic and environmental factors contribute to variation in body mass in a bird population.
One cause of variation in body mass in chickens is infection with the gut protoctist Eimeria. When fed with the same diet, infected chickens have a lower gain in body mass than healthy chickens in the same population.
Suggest one environmental factor that affects the growth and reproduction of Eimeria.
A study was carried out to investigate the effect of treating infected chickens with extracts from a plant, Bidens pilosa.
B pilosa is used in traditional medicine for the treatment of some infectious diseases. - Three populations, each containing 25 chickens infected with Eimeria were observed. - The body mass of each chicken was measured at the start of the study. - Each population was given a different treatment for 56 days: - standard diet with no B. pilosa extract - standard diet with low dose of B. pilosa extract - standard diet with high dose of B. pilosa extract. - The body mass of each chicken was measured at the end of the study and the gain in body mass over the 56 days was calculated. - The mean gain in body mass was calculated for each population. The results are shown in Table 3.1.
Table 3.1
A statistical analysis of the results of the study of these three populations confirmed that there was a significant difference in mean gain in body mass between low dose B. pilosa and high dose B. Pilosa extract treatments.
Sketch on Fig. 3.1 curves to show the pattern of variation for gain in body mass in chickens treated with low dose B. pilosa extract and in chickens treated with high dose B. pilosa extract.
Label one curve 'low dose' and the other curve 'high dose'.
Fig. 3.1
The sea blush, Plectritis congesta, is a flowering plant that grows on the west coast of North America.
Individual sea blush plants produce fruit that is either winged or wingless. Investigations have shown that this characteristic is controlled by a single gene with two alleles:
- a dominant winged fruit allele
- a recessive wingless fruit allele.
Fig. 3.1 shows the difference in structure between winged fruit and wingless fruit phenotypes.
Fig. 3.1
A large sample of sea blush fruits was collected and their fruit-wing characteristic was recorded.
Name the type of variation that is shown for the fruit-wing characteristic of the sea blush.
Different sea blush plants can have fruit with different colours.
Suggest two ways in which a new fruit colour could naturally occur in a sea blush population.
Natural selection occurs in populations, such as in populations of sea blush plants.
Explain why natural selection occurs in populations.
Variation exists in populations of a species and this may provide the opportunity for evolution to occur.
Phenotypic variation exists in many forms and has a number of possible causes.
Describe the main factors that are the cause of phenotypic variation.
Outline the theory of evolution.
The theory of evolution is supported by DNA sequence data.
Explain how DNA sequences are used to show evolutionary relationships between species.