Practise variation and selection through data, diagrams and inheritance contexts, from mutation and leaf measurements to adaptive features and population change.
What is a definition of variation?
having two identical alleles of a particular gene
individuals of the same species in one area
differences between individuals of the same species
the way in which new alleles are formed
The Hawaiian happy-face spider, Theridion grallator, is found on several of the Hawaiian islands. Some of the spiders have a very distinctive pattern on their bodies as shown in Fig. 1.3.
Fig. 1.3
Scientists think that the pattern on the bodies of the spiders is an adaptive feature. Explain the term adaptive feature with reference to this pattern.
Sickle-cell anaemia is an inherited disease.
Fig. 5.1 is a photomicrograph of some blood cells from a person who has sickle-cell anaemia.
Fig. 5.1
Sickle-cell anaemia is most common in areas of the world where the infectious disease malaria is found.
Some species of the genus Plasmodium cause malaria in humans.
The distribution of sickle-cell anaemia is the result of natural selection.
Explain the distribution of the sickle-cell allele in human populations.
Carp are a type of fish. Researchers in Brazil measured the body lengths of a population of carp in a river in 1998 and again in 2008.
Histograms of their results are shown in Fig. 2.1.
Fig. 2.1
Describe the variation in body length of the carp population in 1998. Use the data in Fig. 2.1 to support your answer.
Body length is an example of continuous variation.
Suggest what causes the variation in body length in a population of fish.