22 7 The photograph shows a tawny owl. These owls live in areas close to the Arctic Circle. (Source: © LINDA WRIGHT/SCIENCE PHOTO LIBRARY) Scientists investigated the feather colours of a population of tawny owls. Feather colours of the owls were scored on a scale of 1 to 11, according to how grey or brown they were. Grey feathered owls were given a score between 6 and 1, with 1 being the most grey. Brown feathered owls were given a score between 7 and 11, with 11 being the most brown. The graph shows the percentages of owls in the population with each of the colour scores. 1 11 10 9 8 7 6 5 4 3 2 35 30 25 20 15 10 5 0 Colour score Percentage of owls with colour score (%) Grey Brown (a) The scientists concluded that feather colour in owls is controlled by a single genetic locus. The brown allele is dominant to the grey allele. (i) State what is meant by a dominant allele. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... Turn over 23 (ii) Explain the range of feather colours, shown in the graph, in this population of owls. 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(iii) In this population of 120 owls, 84 of them were grey. Calculate the number of owls that are heterozygous for feather colour. Use the Hardy-Weinberg equation p2 + 2pq + q2 = 1 (3) Answer .............................................................. 24 *(b) The scientists investigated the effect of climate change on the frequencies of these two alleles for feather colour in populations of tawny owls. The percentage survival rates of both colours of owl were measured when there were different depths of snow. The mean depth of snow was recorded each year between 1980 and 2007. The percentage of owls that were coloured brown between 1960 and 2007 was also recorded. The graphs show the results. 0 5 10 15 20 25 100 80 60 40 20 0 Snow depth / cm Percentage of owls that survive (%) grey owls brown owls 1980 2010 2005 2000 1995 1990 1985 25 20 15 10 5 0 Year Mean snow depth / cm 1960 2010 2000 1990 1980 1970 50 40 30 20 10 0 Year Percentage of owls that are brown (%) Turn over 25 The scientists concluded that increased greenhouse gases from human activity are resulting in an increase in the frequency of the brown allele. Analyse the data to evaluate this conclusion. 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(Total for Question 7 = 12 marks)