Evolution (A Level only) (AQA A Level Biology)

The waste material from a zinc mine was left in a grassland habitat. This eventually created a new habitat with high concentrations of zinc in the soil. High levels of zinc are toxic to plants, so no plants were able to grow in this new habitat.

After many years, scientists found a population of daisies growing in this toxic habitat. The daisies belonged to a species (Arctotis acaulis) that normally only grew in the grassland surrounding the mining site. 

Explain how natural selection could produce a zinc-tolerant population of Arctotis acaulis in the mine waste.

The scientists found that individuals from the population of zinc-tolerant Arctotis acaulis flowered at a different time to individuals from the population of Arctotis acaulis growing in the surrounding grassland habitat, which were not zinc-tolerant.

Explain how this might eventually lead to the production of a new species of daisy.

Name and define the type of speciation that could occur between the two populations of Arctotis acaulis described in parts (a) and (b).  

Give two genetic causes of variation between the different members of a population. 

The Pyrenean desman (Galemys pyrenaicus) is a small, semi-aquatic, globally threatened mammals related to moles and shrews. It lives in the Pyrenees which is a mountain range between France and Spain. During a study that lasted many years, scientists found that the number of desman travelling from the population on the northern, French side of the mountain range to the population on the southern, Spanish side of the mountain range was extremely low. The scientists suspect that the original desman species may have split into two different species.

If this is true, explain how this may have occurred.

The scientists found that individual desmans in the northern and southern populations showed phenotypic variation.

State two types of factor that cause phenotypic variation between individuals in a population.

Name and define the type of speciation that could occur between the northern and southern populations of desmans described in parts (a) and (b).

State and explain whether genetic drift has a larger impact in smaller populations or in larger populations.

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 introduced that preys on the mice but cannot climb trees. Several years after the snakes were introduced the biologists returned and found that on the island 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.

In their investigation of evolution, how could the biologists use the islands that did not contain snakes.

What kind of selection were the mice in part (a) undergoing? Explain your answer.

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

i) What is a mutation?

ii) Give a simple definition of evolution.

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 and why the claw length of the mice on the islands may be changing.

Mosquitoes spread a disease called malaria. DDT is a pesticide used to kill mosquitoes. DDT is used in many countries in Africa to try 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 (in Africa) over 5 years.

The graph in Figure 1 below shows the biologists’ results.

Figure 1

Explain the results shown by the graph in Figure 1.

Anaemia occurs when the blood cannot carry enough oxygen. Sickle-cell anaemia is a common condition in people from Uganda and more generally, among people of African descent (as well as among people of Middle Eastern or southern Meditarranean descent). It is caused by a mutation that affects one of the polypeptides in haemoglobin molecules. When the concentration of oxygen is low, affected haemoglobin molecules form fibres within red blood cells, causing them to become sickle-shaped. These sickle cells are targeted for destruction by the immune system and only last about 15 days.

Compared to healthy red blood cells, sickle cells have a shorter life span and smaller surface area. Explain why both these differences result in anaemia.

Without medical treatment, people with sickle-cell anaemia often die in childhood. Scientists predicted that in countries without reliable access to medical care, the sickle-cell allele should reduce in frequency. Explain why this would be expected.

Despite the prediction of scientists described in part (c), sickle-cell anaemia remains common in countries without reliable medical care for the condition. Malaria is also prevalent in these countries. The parasite that causes malaria (transmitted between humans by female mosquitoes) enters the human’s red blood cells and uses the oxygen in these red blood cells for their own respiration.

Using all the information provided in parts (b) and (d), suggest why sickle-cell anaemia is common in many countries where malaria is prevalent.

The diagram in Figure 1 below shows a phylogenetic tree of mousebirds of the Coliidae family. Mousebirds are distantly related to woodpeckers and kingfishers.

Figure 1

The white-backed mousebird (Colius colius) lives in southern Africa. Complete Table 1 below to show the classification of the white-backed mousebird.

Table 1

In Africa, there are several species of mousebird. They are thought to have arisen by sympatric speciation.

Explain how sympatric speciation may have occurred.

A group of scientists produced hybrids between two different species of mousebird by fertilising eggs from one species with sperms from another species. Male hybrids had songs that had some features from one of the parent species and some features from the other parent species.

The male hybrids were unable to reproduce. Suggest why.

Explain how crossing over can contribute to genetic variation.

In parts of South America, corn seeds are a vital source of food. Seeds can be kept forlong periods of time. Scientists have been able to discover well preserved stores of seeds. Figure 1 shows a graph with three different lengths of seeds collected from different seed stores of different ages.

Figure 1

Use Figure 1 and your knowledge of genetics and selection to explain the changes in the mean length of seeds between 1650 and 1900.

Suggest two reasons why corn seeds have increased in length between 1650 to 1900.

Some of the scientists suggested that the variation of seed lengths represent different species of corn. 

Describe a method that could be used to determine if the scientist's statement is correct. 

There are 72 known species of the genus Lygodactylus, many of them found in the continent of Africa and inhabit the same area.

One of these species is the lizard Lygodactylus williamsi is more commonly known as a dwarf gecko. 

Scientists were investigating the number of different Lygodactylus species in one part of East Africa. Describe one way in which scientists could distinguish if the different types of lizards belong to the same species.

The dwarf gecko lives in the leaf crown of screw pine trees, several metres aboveground, feeding off insects and drinking water from leaves. These trees are located in forest patches in parts of Africa, most especially Tanzania.

Demand for timber for firewood and charcoal production in Tanzania is exceptionally high.

Suggest and explain how speciation may occur as a result of deforestation. 

Many species of lizards are similar in size and have few differences in their appearance, apart from their colour. 

Suggest how the variety of colour patterns displayed by lizards may help to maintain the lizards as separate species. 

Dominant male dwarf geckos have a vivid blue colour but females and subordinate males have a copper or green colour. Figure 1 shows a graph that represents the abundance of different colours in a population. 

Figure 1

Using Figure 1, state and explain the type of variation shown and explain how this type of variation arises.

Define what is meant by a gene pool.  

Rhagoletis pomonella is otherwise known as the apple maggot fly. Initially, these maggots would lay their eggs on hawthorn fruit. In the 19th century a distinct group of maggots emerged that lay their eggs on apples only. Apples and hawthorn fruit are closely related. 

Use this information to suggest how these two species of maggots arose by sympatric speciation. 

Apple maggot flies tend to exist in smaller population groups. Scientists in North America were studying a group of apple maggot flies in an apple orchard. The farmer was reducing the size of the orchard to make room for grazing cattle. Table 1 shows the size of the apple orchard and the estimated population size. 

 Table 1

Use Table 1 to calculate the percentage change in the population of apple maggot flies from 1993 to 2018.

The apple orchard had over 300 trees in 1993, reducing to only 70 in 2018. Scientists estimated the population size by sampling 5 trees from 8 randomly selected areas of the orchard between June and July. They concluded that the reduction in orchard size caused a significant decrease in apple maggot flies between 1993 and 2018. 

Using Table 1 and your own knowledge, evaluate the scientist’s conclusion.

The Galapagos Islands are a group of small islands 600 miles off the coast of South America. They are the site of Charles Darwin's famous study of finches. The islands are home to many endemic species of animals and plants which means these species are not found anywhere else. 

Explain how populations can become geographically isolated and how it can lead to speciation

Another species found on the Galapagos islands are the Galapagos lava lizards. These lizards are found on 12 islets that were likely to have been connected to a larger island called Isla Santa Cruz. 

Explain how the smaller populations of lava lizards on these islets may lead to speciation over time.

Use the information provided in part b) to state the name given to the type of speciation the lava lizards may experience. 

The finches on the Galapagos Islands show genetic variation between the islands. One way that variation can arise in populations is by random mutations within genes.

Describe another way in which genetic variation can arise.

The levels of lactose intolerance vary across the world. Table 1 shows the different levels of intolerance in two different populations. 

Table 1

The lactose digesting gene is dominant and allows people to digest lactose in their diet. 

Using Table 1, calculate the percentage difference in the frequency of heterozygous genotype in the Australian aborigines population compared to the European population.

The gene coding for the production of lactase, the lactose digesting enzyme, is normally switched off after an infant becomes an adult. Most adult mammals are unable to digest lactose and are lactose intolerant. Many humans have a genetic mutation that prevents the gene coding for lactase from being switched off. This allows these groups of humans to access food sources containing lactose such as milk. 

Mutations preventing lactose intolerance have occurred in humans at various times inthe prehistoric past, and in all human races. The lowest levels of lactose intolerance are found in areas such as Europe and North America. Until recently, Australian aborigines had been isolated in their island continent for almost 50,000 years. 

Using the information provided, suggest how the lactose tolerant phenotype may have arisen in European populations.

State the type of selection shown in the Australian aborigines population and explain how this takes place. 

The domestication of large lactating mammals like cattle and goats arose in Europe and parts of Africa between 5,000 to 10,000 years ago. 

Suggest why the frequency of the lactose tolerant phenotype has only recently increased.