Natural Selection (SL IB Biology)

A group of biologists conducted an investigation on a remote archipelago (a collection of islands) in the Pacific Ocean. A species of mouse lives on these islands without any natural predators. The biologists measured the claw length of a large number of these mice.

On half of the islands a species of snake was accidentally introduced that preys on the mice but that cannot climb trees. Several years after the snakes were introduced the biologists returned and found that on the islands with snakes, the claw length of the mice had changed. Some had shorter claws, enabling them to run faster, while others had longer claws, enabling them to climb trees.

Suggest the benefit to the scientists’ investigation of there being islands without any snakes present.

The evolution of long claws in the mice in part (a) was made possible by a mutation in the gene controlling claw length. 

Explain how a mutation could lead to a change in claw length.

When the biologists conducted the investigation in part (a), flooding of the islands was very rare. Now, due to climate change, flooding of the islands occurs more regularly. This flooding can regularly wipe out large numbers of ground-living species.

Using this information and the information from part (a), explain how the claw length of the mice on the islands are likely to be changing now.

Explain how natural selection can account for the development of antibiotic resistant bacterial strains.

The habitat of this rabbit population changed:

• Temperatures dropped
• Snowfall became more frequent

Explain the effect that this would have on the allele frequencies in the rabbit population over time.

After several generations the rabbit population accumulated several phenotypic differences to other rabbit populations in nearby habitats.

Explain how scientists could determine whether rabbits from these populations still belong to the same species.

Mining for gold produces waste rocks and mine tailings, which contain sulfur-bearing minerals. When surface water and shallow groundwater come into contact with these minerals, a chemical reaction occurs which produces sulfuric acid. This process is known as acid mine drainage and it can lower the soil pH to a level where very few plants can survive.

Environmentalists studied the area around an abandoned gold mine and discovered a few specimens of earleaf acacia (Acacia auriculiformis) surviving in the acidic soil. This species typically occurs in more neutral or alkaline soils.

Explain how natural selection could produce a population of Acacia auriculiformis that would be tolerant of the acidic soil found around the mine shaft.

Mosquitoes spread a disease called malaria. DDT is a pesticide used to kill mosquitoes; it is used in many countries in Africa to control the spread of malaria.

Some mosquitoes have an allele that gives them resistance to DDT. A group of biologists studied how frequently this allele occurred in a population of mosquitoes in Uganda over 5 years.

The graph below shows the biologists’ results.

Explain the results shown in the graph.

Calculate the percentage increase in the percentage of mosquitoes that have the allele for DDT resistance from 2017 to 2020.

Describe the process of evolution by natural selection.

Outline why some areas of the human genome are more susceptible to detrimental mutations than others.

Natural selection would not be possible without the presence of variation within a species.

Explain how variation allows natural selection to occur.

Mutation, meiosis and sexual reproduction are all sources of genetic variation.

Outline the way in which each of these factors contributes to variation within a species.

Some of the adjacent subspecies of Ensatina can successfully breed with one another, but the western subspecies E. eschscholtzii cannot interbreed with the eastern subspecies E. klauberi.

Based on the information provided, evaluate the claim made by some scientists that the different subspecies of Ensatina should be classified as separate species.

The turtle-headed sea snake, Emydocephalus annulatus, can be found in waters off the coast of Australia, New Zealand and New Caledonia. These snakes usually have banded patterns of white with dark rings, although some individuals exhibit a single dark colour with no banded patterns. The dark parts of the skin contains a high concentration of the pigment melanin, which binds to certain trace elements present in the water. These trace elements are removed from the body when the snake sloughs off the skin. It was found that melanic sea snakes will slough off the skin more frequently than those with banded colouration.

Scientists studied the frequency of melanic sea snakes from several sites in waters surrounding urban-industrial areas and waters from non urban-industrial areas. The results are shown in the table below.

Calculate the percentage difference in the mean frequency of melanic snakes found in urban-industrial waters and those that were present in non urban-industrial waters.

Based on the information provided in part a), deduce the adaptive advantage of melanism to turtle-headed sea snakes.

The graph below shows the population sizes of a rabbit and a wolf population over many generations. 

Explain the data in the graph for rabbit and wolf populations over the first 300 generations. 

At generation 350 in the graph shown in part b) the frequency of allele A is high, but never 100%. 

State one reason why it is not beneficial for this population to have one allele at 100% frequency.

The evolution of Black bear body mass happened on Earth thousands of years ago.

Suggest how scientists know about their evolutionary past. 

The evolution of some species can be driven by female mating preferences, e.g. in a species of bird called the long-tailed widowbird, females have a preference for males with long tails. The long tails of male widowbirds have evolved from short-tailed ancestors despite being heavy and limiting male flying ability.

Discuss the selection process that has resulted in long tails in male widowbirds.