Tut 14 - Natural selection Evolution

St Andrew’s Junior College Diversity & Evolution / Natural Selection & Evolution 2022 H1 Biology 1 Full Name: Civics group: 21S Index no.: Date: Biological Evolution Natural Selection and Evolution Tutorial 14 1 2 3 4 5 6 7 8 9 10 11 12 C B A C D A A B B C A A 1 A population of squirrels is preyed upon by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome? A Stabilizing selection B Directional selection C Disruptive selection (conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes.) D Balancing selection 2 Birds with average sized wings survived a severe storm more successfully than other birds in the same population with longer or shorter wings. If severe storms occur regularly, then over time, one should expect these storms to bring about A the bottleneck effect B stabilizing selection extreme phenotypes are selected against C artificial selection E disruptive selection 3 Which type of selection maintains stable frequencies of two or more phenotypic forms in a population? A Balancing selection B Neutral variation C Heterozygote advantage D Stabilizing selection

St Andrew’s Junior College Diversity & Evolution / Natural Selection & Evolution 2022 H1 Biology 2 4 A number of mosquito populations today are resistant to insecticides that were once effective. Biologists think that insecticide resistance evolved in mosquitoes because A individual mosquitoes built up immunity to an insecticide after being exposed to it. B mosquitoes needed to develop insecticide resistance to survive after the insecticide was used. (development of insecticide resistance arose due to spontaneous mutation, not because of a need) C a few mosquitoes were probably resistant to the insecticide before it was ever used and these individuals were more likely to survive and reproduce. D use of insecticides induced mutations in mosquitoes, resulting in resistance to these insecticides (development of insecticide resistance arose due to spontaneous mutation. it is a random process and it is not something that can be controlled) Comment: Options A, B & D are indicative of Lamarck’s theory and hence are incorrect. 5 The diagram shows a form of selection operating within a population over three generations, 1, 2 and 3. Organisms in the shaded areas are selected against. What can be concluded from these results? A Loss of individuals with phenotypes close to the most common value suggests that the variation in the phenotypic characteristic has an environmental cause. (cannot tell, could be due to artificial selection) B One species is split, in three generations, i nto two species that are reproductively isolated from one another. (cannot tell if the two populations are reproductively isolated from one another) C The population is divided into two groups in three generations because the selection is artificial. (cannot tell, could be due to natural selection) D Two groups of individuals are formed in three generations whose ranges of variation for the phenotypic characteristics do not overlap. 6 Zebras with some horizontal stripes are bitten less frequently by tsetse flies than those with only vertical stripes. The flies carry diseases that infect zebras. Phenotypic characteristic Phenotypic characteristic Phenotypic characteristic Frequency Frequency Frequency Generation 1 Generation 2 Generation 3

St Andrew’s Junior College Diversity & Evolution / Natural Selection & Evolution 2022 H1 Biology 3 Which combination of statements could explain an increase in the proportion of individuals with horizontal stripes in a population of zebras over several generations? 1 Tsetse flies are the selection pressure. (true, the presence of flies will select for zebras with horizontal stripes. Zebras with horizontal stripes have a selective advantage over zebras with only vertical stripes) 2 Compared with other zebras, zebras with horizontal stripes are less likely to get diseases from tsetse flies. (true as these zebras are bitten less frequently) 3 On average, zebras with horizontal stripes live longer and produce more offspring than other zebras. (true as these zebras are less likely to get diseases carried by tsetse flies) 4 Zebras with horizontal stripes pass the alleles responsible for these stripes to their offspring. (true, fit individuals will produce similar offspring as alleles encoding for the beneficial trait will be passed down to the next generation) A 1, 2, 3 and 4 B 1, 2 and 4 only C 1, 3 and 4 only D 2 and 3 only 7 The graph below shows the distribution of huntsman spiders at a forest boundary: One species of huntsman spider (Isopeda isopedella) varies in body colour from dark brown to light grey. In one community at the forest boundary, two populations of this species were found. Some were found living inside the forest and others were found living just outside the forest. The relative numbers of dark brown adult spiders and light grey adult spiders found at certain distances from the forest boundary are shown in the graph above. Which of the following can be least inferred from the graph?

St Andrew’s Junior College Diversity & Evolution / Natural Selection & Evolution 2022 H1 Biology 4 A At the forest boundary, the selection pressure is stronger than that either inside the forest or outside the forest. (typically results in directional selection) B The plateau in the population number as seen inside the forest and outside the forest is due to competition among the adult spiders for resources. (competition helps to stabilise the population numbers) C The lower plateau of spider population outside the forest compared to that of inside the forest is due to the presence of additional selection pressure existing outside the forest. (additional selection pressure further population numbers) D Dark brown huntsman spiders are not eaten by birds inside the forest as their colour allows them to camouflage and hence provides a selective advantage. (able to survive till maturity and reproduce, that is why their numbers are higher inside forest) 8 Tay-Sachs disease, which is lethal, results from having the homoz ygous recessive condition of the responsible gene. Which one of the following statements is true? A Only homozygous dominant individuals will be able to survive and reproduce. (heterozygous individuals can also survive and reproduce) B Heterozygous individuals will survive and may pass the recessive allele on to their offspring. C In the heterozygous condition, the dominant allele will overcome the recessive allele and only the dominant allele will be passed on to offspring. (50% chance that dominant allele will be passed on, 50% chance that recessive allele will be passed on) D Homozygous dominant individuals will be more likely to reproduce than heterozygous individuals. (both do not exhibit disease phenotype, hence both are equally fit – ie able to survive till maturity and reproduce) 9 The figure below shows an aerial view of a region which included a section of copper contaminated soil (shaded grey on the diagram). The black circles represent populations of grass growing in areas A, B and C. The figure also includes the percentage of copper resistant plants in areas A, B and C. Tolerance to copper in the soil is genetically determined.

St Andrew’s Junior College Diversity & Evolution / Natural Selection & Evolution 2022 H1 Biology 5 It is reasonable to conclude from the information that 1 most plants in the copper contaminated area would be homozygous at the