Natural and artificial selection

Fig. 7.1 shows a red deer, Cervus elaphus. Red deer are herbivores that eat many different kinds of plants. Table 7.1 shows that the number of red deer in the UK rose between 1960 and 2010.

Feb/March 2018

Mexican spadefoot toads, Spea multiplicata, spend most of their lives on land, but they go back to ponds to reproduce. Eggs are deposited in water and hatch into tadpoles, which feed in ponds before becoming adults. The tadpoles can be grouped into two broad types: omnivore-type tadpoles and carnivore-type tadpoles. The phenotype differences between these two tadpole types are linked to their different feeding habits. Omnivore-type tadpoles consume tiny fragments of detritus (dead material from plants and animals) and algae (microscopic photosynthetic organisms) at the bottom of ponds. These tadpoles grow slowly. Carnivore-type tadpoles eat small animals in the water, such as fairy shrimp and small omnivore tadpoles. These tadpoles grow rapidly. Fig. 4.1 shows two tadpoles of the same age, one of each type. A fairy shrimp is also shown. All three organisms are the same distance from the camera. Between these two main types of tadpole there is a continuous range of tadpoles with intermediate body phenotypes and feeding habits. For any individual tadpole, regardless of age, a phenotype score can be calculated from the tadpole's features. A tadpole with a phenotype score close to 3 is a typical omnivore type, whereas a tadpole with a phenotype score close to 7 is a typical carnivore type. Phenotype scores were measured for a large number of tadpoles sampled from two ponds. In one pond, detritus and algae were abundant, whereas in the other pond they were scarce. All other conditions in the two ponds were similar. For both ponds, phenotype scores were measured soon after the tadpoles had hatched from eggs and again ten days later.

Feb/March 2019

The European hedgehog, Erinaceus europaeus, is a small mammal that eats both plant and animal matter. Its body is covered with spines, which are usually brown. A rare variant, which does not have the brown pigment, has blonde (pale yellow) spines. This characteristic is controlled by a recessive allele. Fig. 1.1 shows a European hedgehog with blonde spines. Alderney is a small island between the UK and France. Hedgehogs were absent from Alderney until the 1960s, when three pairs of hedgehogs were brought onto the island. The hedgehogs began to breed and some of the offspring had blonde spines. By 2017, the hedgehog population, including individuals with brown spines and individuals with blonde spines, had risen to approximately 600.

Feb/March 2022

Holstein Friesian cattle are a cattle breed that dairy farmers in many countries use because their cows give a high milk yield. In Holstein Friesian cattle, milk yield is influenced by heat stress. Heat stress happens when homeostatic mechanisms are insufficient to keep body temperature at normal levels. Air temperature is one factor that adds to heat stress. Fig. 4.1 shows Holstein Friesian cattle. Fig. 4.2 presents the mean daily air temperature in Central Europe and the mean monthly milk yield per cow of Holstein Friesian cattle in Central Europe.

Feb/March 2024

This passage summarises the key ideas of natural selection, with several words left out.

May/June 2011

This passage summarises the key ideas behind natural selection. Several words have been left out.

May/June 2011

Using Fig. 4.1, explain how any two characteristics of this flower make it adapted for wind pollination.

May/June 2012

Hippocampus, the seahorse, is a small and unusual fish. It produces live young, and the male rather than the female is the one that becomes pregnant. Fig. 1.1 shows a seahorse.

May/June 2012

Sarawak is a region in south-east Asia and is mostly covered by tropical rainforest. Logging has been permitted in large areas of the forest. A study was carried out to estimate the population size of different species of mammals living in the rainforest: • before any logging took place • straight after logging • two years after logging • four years after logging. Table 8.1 gives the results of the study for six mammal species. When the numbers were too small for population density to be measured, the species were recorded as "present".

May/June 2013

The filamentous fungus, Fusarium venenatum, may be cultivated in a fermenter and then collected as mycoprotein. It is marketed as food in several different countries. The fungus is produced in continuous culture in $150\,000\,\text{dm}^3$ airlift fermenters, where compressed air bubbles both supply oxygen and mix the contents. Because the fungus grows as thin, branched filaments, the harvested mycoprotein has a naturally chewy, fibrous texture. About $300\,\text{kg}$ of fungus can be harvested each hour.

May/June 2013

Myostatin is a protein made in mammalian skeletal muscle cells. It travels in the bloodstream and acts on muscle tissue to reduce any further differentiation and growth. In thoroughbred racehorses, a mutation caused by the substitution of a single nucleotide has been found in the MSTN gene that codes for myostatin. At this mutation site, the DNA nucleotide is either a cytosine (C) base or a thymine (T) base, so race horses have three possible genotypes for this mutation: CC, CT or TT.

May/June 2014

Collared lizards, Crotaphytus collaris, vary in body length and running speed. An investigation was done to discover whether body length and running speed influenced how many offspring a male lizard sired. A large number of male lizards was trapped during the breeding season. For each lizard, body length was measured, it was chased along a short race track and its top running speed over $1\,\text{m}$ was recorded, and a blood sample was collected and DNA sequences at $10$ different loci were analysed. The lizards were then released back into the place where they had been caught, so that mating could take place. Several weeks later, after the lizards’ eggs had hatched, as many young hatchlings as possible were captured. DNA testing was carried out on each hatchling to identify which male was the father. The results were then used to work out the number of offspring sired by each of the male lizards in the initial sample.

May/June 2014

The monkey flower, Mimulus guttatus, is pollinated by bumblebees rather than by self-pollination. Because bumblebee numbers are declining in many parts of the world, an experiment was done in Kansas to see how these plants are affected when pollinators are lost. - 1600 Mimulus plants were grown in a field. - 1600 Mimulus plants were grown in a glasshouse that bumblebees were unable to enter. For several generations, seeds were collected and sown again and again at both sites. At the start, the glasshouse plants produced few seeds, but after five generations they were able to self-pollinate and the number of seeds produced was almost the same as that of the field plants. By the end of five generations, the flowers of the glasshouse plants were significantly smaller than those of the field plants.

May/June 2015

Artificial selection has been practised for thousands of years. One example is the Santa Gertrudis breed of cattle, which grow quickly and can tolerate high temperatures and high humidity. This breed was developed from the following two breeds: English shorthorn cattle, which grow quickly but do not tolerate high temperatures and high humidity; Brahman cattle from India, which tolerate high temperatures and high humidity.

May/June 2015

The monkey flower, Mimulus guttatus, is pollinated by bumblebees through cross-pollination, and it does not self-pollinate. Because bumblebee numbers are declining in many parts of the world, an experiment was done in Kansas to find out what effect the loss of pollinators would have on these plants. 1600 Mimulus plants were grown in a field. Another 1600 Mimulus plants were grown in a glasshouse that bumblebees could not enter. Seeds were collected and sown repeatedly for several generations at each site. Initially, the glasshouse plants produced few seeds, but after five generations they were able to self-pollinate and the number of seeds produced was almost the same as that of the field plants. After five generations, the flowers of the glasshouse plants were significantly smaller than those of the field plants.

May/June 2015

Maize is a major food crop that has been improved through both selective breeding and genetic modification.

May/June 2016

Wheat and other food crops can be improved through selective breeding and genetic modification.

May/June 2016

Maize is a major food crop that has been enhanced through selective breeding and genetic modification.

May/June 2016

The red poppy, Papaver rhoeas, along with several daisy species in the family Compositae, often occur together as weeds in wheat fields. Fig. 5.1 illustrates how the percentage frequency of red poppies and daisies changed in one area of wheat fields during the six year period from 1998 to 2003. From 1985, the herbicide metsulfuron-methyl was used to control weeds in this wheat-field area, and this continued throughout the six year period. In 1998, the first red poppy of biotype X appeared. This red poppy possessed a particular mutation that was absent from ordinary red poppies.

May/June 2017

Weeds lower crop yields because they compete with crop plants for space, light, water and minerals. Table 4.1 summarises the modes of action of three different herbicide types. Fig. 4.1 shows the cumulative number of weed species that have developed resistance to these three herbicide types since 1960.

May/June 2017

The red poppy, Papaver rhoeas, together with several daisy species in the family Compositae, frequently occur side by side as weeds in wheat fields. Fig. 5.1 illustrates how the percentage frequencies of red poppies and daisies changed in one area of wheat fields during a six year interval from 1998 to 2003. From 1985, metsulfuron-methyl was applied as a herbicide to control weeds in this wheat-field area. This continued for the whole six year period. In 1998, the first red poppy biotype X appeared. This red poppy possessed a particular mutation that was absent from ordinary red poppies.

May/June 2017

Researchers have detected only minimal evolutionary change within populations of two Australian songbirds: the zebra finch, $\textit{Taeniopygia guttata castanotis}$, and the budgerigar, $\textit{Melopsittacus undulatus}$.

May/June 2018

An investigation was undertaken into natural selection in the plant evening primrose, Oenothera biennis.

May/June 2018

Scientists examined how strongly the founder effect and natural selection influenced evolutionary change. Fig. 5.1 shows the brown anole lizard, $Anolis\ sagrei$. These lizards occur on several Caribbean islands and eat many kinds of invertebrates and other small animals. $A.\ sagrei$ spends much of its time perched (resting) on, or travelling along, branches of shrubs and trees. The width of the branch on which $A.\ sagrei$ perches is called the perch diameter. There is a positive correlation between perch diameter and hind limb length of $A.\ sagrei$. In 2004, a hurricane killed all the $A.\ sagrei$ lizards on seven islands. In 2005, researchers randomly took seven male and seven female lizards from a source population on a nearby island and founded new populations on each island. Fig. 5.2 shows the variation in vegetation between the source island and the seven experimental founder islands.

May/June 2019

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.

May/June 2019

Using named examples, describe and explain how continuous variation differs from discontinuous variation.

May/June 2020

Humans use selective breeding to improve the characteristics of crop plants and domesticated animals.

May/June 2021

In continuous variation, a population displays a spectrum of phenotypes between two extremes, with no clear-cut groups. Height and mass are examples of phenotypic traits that show continuous variation.

May/June 2021

Explain what stabilising selection means.

May/June 2021

$\textit{Oryza}$ is the genus of grass plants that contains rice, $\textit{Oryza sativa}$, which is a food crop.

May/June 2023

Humans use antibiotics to treat bacterial infections. As antibiotics have been used more widely, the number of bacteria strains resistant to antibiotics has risen. The development of antibiotic resistance in bacteria has been driven by natural selection.

May/June 2023

The Galápagos form an island group with very high biodiversity.

May/June 2025

Natural selection and selective breeding (artificial selection) are two processes that bring about changes in the gene pool of a population. These processes have consequences for humans.

May/June 2025

The bacterium that causes disease, Pseudomonas aeruginosa, can sometimes be present as a ‘biofilm’. A biofilm is a bacterial layer growing on a surface and attached to another surface. Antibiotics have difficulty controlling such biofilms. A mutant strain of P. aeruginosa has been identified that forms biofilms indistinguishable from those made by the wild-type bacteria. Even so, the mutant strain is different from the wild-type in how resistant it is to antibiotic A. Antibiotic A is in the antibiotic group called anti-pseudomonal penicillins.

Oct/Nov 2010

In sickle cell anaemia, the recessive allele Hb$^{S}$ takes the place of the normal allele Hb$^{A}$. Hb$^{S}$ occurs at a far greater frequency in West Africa than in most other regions of the world. The frequency of Hb$^{S}$ matches the geographical distribution of malaria.

Oct/Nov 2010

In sickle cell anaemia, the recessive allele $\mathrm{Hb}^S$ takes the place of the normal allele $\mathrm{Hb}^A$. The frequency of $\mathrm{Hb}^S$ is much greater in West Africa than in most other regions of the world, and this pattern matches the spread of malaria.

Oct/Nov 2010

From 1975 to 1977, one of the Galapagos Islands, Daphne Major, went through a drought. On Daphne Major, the ground finch, Geospiza fortis, feeds on seeds. One of the few plants that survived the drought produced large seeds inside hard fruits. Many G. fortis died during the drought, so the population fell from 1400 in 1975 to 190 in 1977. The mean beak depth of the G. fortis that died was 10.68 mm, while the mean beak depth of those that survived was 11.07 mm. Before the drought, the mean beak depth of G. fortis was 10.86 mm.

Oct/Nov 2010

This passage outlines the main principles of artificial selection. Several words have been omitted.

Oct/Nov 2011

Section B. Answer only one question.

Oct/Nov 2012

Penicillin-binding proteins (PBPs) are proteins located in the cell surface membrane of bacteria. PBPs catalyse the last stages in the formation of a peptidoglycan cell wall.

Oct/Nov 2012

Section B. Choose and answer one question.

Oct/Nov 2012

All present-day dog breeds are members of one species and are believed to have arisen from 14 ancient breeds through artificial selection. The golden retriever is a modern breed that is often trained as a guide dog for people who are blind or visually impaired. Fig. 1.1 depicts a golden retriever.

Oct/Nov 2014

All dog breeds that are modern belong to one species and are considered to have come from 14 ancient breeds through artificial selection. The golden retriever is a modern breed that is frequently used as a guide dog for people who are blind or visually impaired. Fig. 1.1 shows a golden retriever.

Oct/Nov 2014

Bread wheat, $\textit{Triticum aestivum}$, is a hexaploid that arose from diploid wild grasses.

Oct/Nov 2015

In shorthorn cattle, coat colour is determined by a codominant pair of alleles. The coat may be red, white or roan, and roan is a red-and-white mixture. A separate pair of alleles controls whether horns are present. The allele for horns is recessive to the allele for hornless cattle.

Oct/Nov 2015

Atlantic salmon, $Salmo\ salar$, is a major fish species reared for human food. Fig. 3.1 illustrates an Atlantic salmon. Infectious pancreatic necrosis (IPN) is a severe viral disease that is currently affecting farmed salmon.

Oct/Nov 2015

In rural India, the main way of controlling a species of $Anopheles$ mosquito is to spray insecticide on the inner walls of houses. Several different insecticides have been used. For many years, malathion was the principal insecticide. In 2005, this was replaced by the newer insecticide, deltamethrin, and malathion was no longer used. A laboratory investigation was done with mosquitoes gathered from two sites in India. The proportion of mosquitoes killed by malathion and deltamethrin was estimated. The findings are shown in Table 4.1.

Oct/Nov 2016

The principal way of controlling a species of $\textit{Anopheles}$ mosquito in rural India is to spray insecticide onto the interior walls of houses. Several different insecticides have been used. For many years, malathion was the main one. In $2005$, this was replaced by the newer insecticide deltamethrin, and malathion use stopped. A laboratory investigation was done with mosquitoes collected from two sites in India. The proportion of mosquitoes killed by malathion and deltamethrin was estimated. The findings are shown in Table 4.1.

Oct/Nov 2016

Drug therapy is the chief way malaria cases are treated. Several different drugs have been used to destroy a species of the Plasmodium parasite that causes malaria. For many years, chloroquine was the main drug used in Africa. In 1996, the newer drug sulfadoxine-pyrimethamine (Fansidar), replaced it and chloroquine use was stopped. A study was done to estimate the percentage of parasites killed by the two different drugs in two African countries. The findings of the study are shown in Table 4.1.

Oct/Nov 2016

Fig. 3.1 presents a red squirrel, $\textit{Sciurus vulgaris}$. This species is native to the British Isles, which means it has been present there for at least 10000 years. During the 1800s, a closely related but slightly larger species, the grey squirrel, $\textit{Sciurus carolinensis}$, was brought in from North America. The history of interactions between red squirrels and grey squirrels includes the following points: - Grey squirrels, which occupy a similar niche to red squirrels, spread through their range very quickly after introduction. - Grey squirrels carry a virus that does not affect them, but which is lethal to red squirrels. - Red squirrels died out in many areas of the British Isles. - More recently, some places have shown the opposite pattern. Grey squirrel numbers have fallen. Red squirrels have returned to their former habitats. - This has occurred in areas where the native predator, the pine marten, $\textit{Martes martes}$, has been protected, causing the number of these predators to rise. - Examination of pine marten faeces shows that they capture and eat many more grey squirrels than red squirrels.

Oct/Nov 2017

Meiosis is a process that helps to create genetic variation.

Oct/Nov 2018

Researchers have discovered evidence that humans have undergone natural selection.

Oct/Nov 2018

A $28$-year investigation of Magellanic penguins, Spheniscus magellanicus, in Argentina supplies evidence for natural selection. Magellanic penguins lay eggs in nests. They use their bills (beaks) to seize prey and to feed their chicks (offspring) in the nest. Each breeding pair returns to the same nest every year. Bill size data were gathered annually from 1983 to 2010. Bill size was worked out from bill length and bill depth. There was variation in bill size among individuals. In 1983, all penguins in one area were tagged. Each year, all tagged penguins were measured, and their new chicks were tagged and measured too. For every year in the study, food availability was estimated. A statistical analysis was then carried out to determine whether selection had occurred.

Oct/Nov 2019

Selective breeding has been employed to enhance the traits of crop plants, including maize and rice.

Oct/Nov 2022

Selective breeding has been used to improve crop plant characteristics, including those of maize and rice.

Oct/Nov 2022

Evidence suggests that selective breeding started around 10000 years ago. Selective breeding has been important in helping to meet the worldwide demand for food.

Oct/Nov 2023

Green lacewings form an insect family containing over 1300 species. The common green lacewing, Chrysoperla carnea, is displayed in Fig. 9.1.

Oct/Nov 2023

Spea multiplicata is among the American spadefoot toad species. The young stage of spadefoot toads is the tadpole, and it lives in pond water. In S. multiplicata, genetic variation produces three tadpole phenotypes. These three phenotypes are detritus feeder, intermediate and carnivore. Detritus feeders are small, whereas carnivores are large. Intermediates differ in size and lie between these two extremes. Figure 7.1 shows a detritus feeder and a carnivore. Scientists recorded the number of each tadpole type in two ponds: pond 1 and pond 2.

Oct/Nov 2024

Different processes can alter allele frequencies in populations.

Oct/Nov 2024

Spea multiplicata is among the American spadefoot toad species. The young are tadpoles and live in pond water. Due to genetic variation, S. multiplicata tadpoles display three phenotypes: detritus feeder, intermediate and carnivore. Detritus feeders are the smallest, whereas carnivores are the largest. Intermediates differ in size between these two extremes. Figure 7.1 shows a detritus feeder and a carnivore. Scientists recorded how many of each tadpole type were found in two separate ponds: pond 1 and pond 2.

Oct/Nov 2024

The wolf, Canis lupus, is found in North America. Wolves can have either a grey coat or a black coat. The coat colour of a particular wolf is determined by the DNA it inherits at the CPD103 gene locus. Each wolf inherits two copies of CPD103, one from each parent. A wolf that inherits one copy of the black version of the CPD103 gene has a black coat. Besides giving black coat colour, the protein encoded by the CPD103 gene also protects against infectious lung disease. Canine distemper virus (CDV) causes severe lung disease in wolves. Wolves that were infected by CDV in the past have antibodies against CDV (anti-CDV antibodies) in their blood.

Oct/Nov 2025

The appearance of antibiotic resistance in bacteria has happened because of natural selection.

Oct/Nov 2025

In plant anthers, meiosis and cytokinesis produce pollen grains. The cells that undergo meiosis are called pollen mother cells. Fig. 2.1 shows five meiosis stages in a pollen mother cell.

Oct/Nov 2025