Biology 9700 · AS & A Level · Natural and artificial selection
Natural and artificial selection — practice question
Steelhead trout, Oncorhynchus mykiss, are fish native to streams in North America. Since 1992, captive breeding has been used in an effort to boost steelhead trout numbers. Eggs and sperm are combined, and the young fish spend their first year in large tanks of aerated water. Most of these fish are later returned to the wild, although some males and females are retained so they can parent the next generation of captive-bred fish. A single tank can contain as many as 50000 fish. The juvenile captive fish are given processed food. Some of the young fish cannot withstand these conditions, so a fraction die. Death is usually caused by poor wound-healing after accidents linked to overcrowding and by the spread of disease.
(a(i))[1]
Identify the expected form of variation in wound-healing ability within a fish population.
(a(ii))[1]
Identify the process that leads to better survival in the second, third and later generations of captive-bred fish.
(b)[3]
Suggest and explain three ways in which conditions in the tank may cause a captive fish to have a phenotype different from that of a wild fish.
(c(i))[5]
Describe how microarray analysis can be used to identify differences in the expression of many genes when two samples are compared, such as the offspring of wild and captive-bred fish.
(c(ii))[4]
Explain how gene expression is regulated in eukaryotes such as fish.
(d(i))[1]
Explain why the researchers concluded that the differences in gene expression between the two groups of fish were inherited.
(d(ii))[1]
Explain why the researchers concluded that the differences in gene expression between the two groups of fish were adaptive.
Worked solution & mark scheme
This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: “continuous variation / normal (bell-shaped) distribution” …