Abitur NRW Biologie 2022 · GK · Haupttermin · bilingual Englisch

Material A: The Biology of the Avian Vampire Fly

The avian vampire fly ( Philornis downsi) is a fly species that is distributed in large areas of South America. This fly was first recorded on the Galapagos Islands in 1960 and was probably introduced there by ship or aircraft. The Galapagos consist of 13 major islands. These islands range up to 1,700 meters in height and provide different habitats from hot, arid lava fields to cold, humid highlands. The avian vampire fly spread rapidly on all major islands.

Adult avian vampire flies feed on fresh as well as on decaying fruits and flowers of different plant species. They lay their eggs in bird nests. The avian vampire fly larvae suck the blood of hatchlings, affecting growth and causing anemia 1, which usually leads to death. A female fly lays up to 180 eggs, which it spreads over 20 to 30 nests of different bird species. A minimum of three fly generations develops in one bird nesting season.

Table 1 A comparison between selected factors of living conditions of the avian vampire fly in its regions of origin in South America, as well as on the Galapagos · Regions of origin in South America · Galapagos Islands

Bird species infested by the avian vampire fly · numerous small passerines 2, including finches, cuckoos and woodpeckers · numerous small passerines, including almost all Darwin finch species and cuckoos

Percentage of nests infested by the avian vampire fly · less than 30 % · more than 90 %

Average number of larvae per nest · fewer than 10 · more than 30

Percentage of avian vampire fly larvae killed by parasitic wasps · 10 % to 20 % · max. 5 %

Predators of the avian vampire fly larvae · ants · none

1 Blutarmut

2 Sperlingsvögel

Material B: Effect of Permethrin on Nerve Cells

The infestation of avian vampire flies has led to a strong decline in the number of Darwin finches. The insecticide permethrin is used to control the avian vampire fly populations on the Galapagos Islands. Insects take up permethrin via their body surface. Treated insects die when a sufficiently high dose is applied, but they can recover if the applied dose is too low. Permethrin binds to voltage-gated sodium channels in the axon membrane. The neurophysiological effects of permethrin were investigated in experiments. For this purpose, insect nerve cells were treated with permethrin and briefly stimulated; the membrane potential was measured (Figure 1).

Material C: The Use of Permethrin to Protect Darwin Finches

The number of Darwin finches decreased significantly on the Galapagos Islands due to the infestation with avian vampire flies, as up to 95 % of the chicks die in the field. In order to protect the bird populations, control measures with the insecticide permethrin were investigated in field experiments.

In a first experiment, dispensers with cotton fibres were set up. The fibres were used by the finches to build their nests. The dispensers for the experiment contained cotton fibres treated with a 1% permethrin solution. The cotton fibres in the control dispensers were treated with water. After hatching, the mass of cotton used to build the nests as well as the number of avian vampire fly larvae were determined (Figure 2).

Nests were sprayed with a 1% permethrin solution or with water in a second field experiment. Then the number of fledged nestlings 3 from these nests were determined (Figure 3).

Another study investigated whether permethrin treatment has any long-term effects on Darwin finches. For this purpose, experiments were carried out in the laboratory with the closely related zebra finch species ( Taeniopygia guttata), as this species is easier to keep and breed than Darwin finches. Two generations of zebra finches were bred for the study. Either nesting material that had been treated with a 1% permethrin solution or with water was used for both generations. The eggs and hatchlings of both generations were investigated and the reproductive success determined.

In the first generation, no significant differences were observed between the control group and the group with nests that had been treated with permethrin. In the second generation there were no significant differences regarding the number of eggs and the number of hatched nestlings, but there were differences in the mortality of nestlings: whereas all nestlings survived in the control nests, 64% survived in the nests treated with permethrin.

3 flügge gewordene Jungvögel

Aufgabenstellung 1

Present a food web that shows the feeding relationships among the species introduced in Material A in their native South American habitats, and work out the trophic levels involved (Material A). Give reasons why the avian vampire fly spread so quickly across the Galapagos Islands (Material A). [19 Punkte]

a)

b)

c)

Material A: The Biology of the Avian Vampire Fly

The avian vampire fly ( Philornis downsi) is a fly species that is distributed in large areas of South America. This fly was first recorded on the Galapagos Islands in 1960 and was probably introduced there by ship or aircraft. The Galapagos consist of 13 major islands. These islands range up to 1,700 meters in height and provide different habitats from hot, arid lava fields to cold, humid highlands. The avian vampire fly spread rapidly on all major islands.

Adult avian vampire flies feed on fresh as well as on decaying fruits and flowers of different plant species. They lay their eggs in bird nests. The avian vampire fly larvae suck the blood of hatchlings, affecting growth and causing anemia 1, which usually leads to death. A female fly lays up to 180 eggs, which it spreads over 20 to 30 nests of different bird species. A minimum of three fly generations develops in one bird nesting season.

Table 1 A comparison between selected factors of living conditions of the avian vampire fly in its regions of origin in South America, as well as on the Galapagos · Regions of origin in South America · Galapagos Islands

Bird species infested by the avian vampire fly · numerous small passerines 2, including finches, cuckoos and woodpeckers · numerous small passerines, including almost all Darwin finch species and cuckoos

Percentage of nests infested by the avian vampire fly · less than 30 % · more than 90 %

Average number of larvae per nest · fewer than 10 · more than 30

Percentage of avian vampire fly larvae killed by parasitic wasps · 10 % to 20 % · max. 5 %

Predators of the avian vampire fly larvae · ants · none

1 Blutarmut

2 Sperlingsvögel

Material B: Effect of Permethrin on Nerve Cells

The infestation of avian vampire flies has led to a strong decline in the number of Darwin finches. The insecticide permethrin is used to control the avian vampire fly populations on the Galapagos Islands. Insects take up permethrin via their body surface. Treated insects die when a sufficiently high dose is applied, but they can recover if the applied dose is too low. Permethrin binds to voltage-gated sodium channels in the axon membrane. The neurophysiological effects of permethrin were investigated in experiments. For this purpose, insect nerve cells were treated with permethrin and briefly stimulated; the membrane potential was measured (Figure 1).

Material C: The Use of Permethrin to Protect Darwin Finches

The number of Darwin finches decreased significantly on the Galapagos Islands due to the infestation with avian vampire flies, as up to 95 % of the chicks die in the field. In order to protect the bird populations, control measures with the insecticide permethrin were investigated in field experiments.

In a first experiment, dispensers with cotton fibres were set up. The fibres were used by the finches to build their nests. The dispensers for the experiment contained cotton fibres treated with a 1% permethrin solution. The cotton fibres in the control dispensers were treated with water. After hatching, the mass of cotton used to build the nests as well as the number of avian vampire fly larvae were determined (Figure 2).

Nests were sprayed with a 1% permethrin solution or with water in a second field experiment. Then the number of fledged nestlings 3 from these nests were determined (Figure 3).

Another study investigated whether permethrin treatment has any long-term effects on Darwin finches. For this purpose, experiments were carried out in the laboratory with the closely related zebra finch species ( Taeniopygia guttata), as this species is easier to keep and breed than Darwin finches. Two generations of zebra finches were bred for the study. Either nesting material that had been treated with a 1% permethrin solution or with water was used for both generations. The eggs and hatchlings of both generations were investigated and the reproductive success determined.

In the first generation, no significant differences were observed between the control group and the group with nests that had been treated with permethrin. In the second generation there were no significant differences regarding the number of eggs and the number of hatched nestlings, but there were differences in the mortality of nestlings: whereas all nestlings survived in the control nests, 64% survived in the nests treated with permethrin.

3 flügge gewordene Jungvögel

2. Present the neurobiological events taking place during an action potential as a flowchart, and sum up the findings shown in Figure 1B (Material B). Illustrate how permethrin affects neurophysiological processes and, based on this, deduce what this means for the insect (Material B).

[21 Punkte]

a)

b)

c)

d)

Material A: The Biology of the Avian Vampire Fly

The avian vampire fly ( Philornis downsi) is a fly species that is distributed in large areas of South America. This fly was first recorded on the Galapagos Islands in 1960 and was probably introduced there by ship or aircraft. The Galapagos consist of 13 major islands. These islands range up to 1,700 meters in height and provide different habitats from hot, arid lava fields to cold, humid highlands. The avian vampire fly spread rapidly on all major islands.

Adult avian vampire flies feed on fresh as well as on decaying fruits and flowers of different plant species. They lay their eggs in bird nests. The avian vampire fly larvae suck the blood of hatchlings, affecting growth and causing anemia 1, which usually leads to death. A female fly lays up to 180 eggs, which it spreads over 20 to 30 nests of different bird species. A minimum of three fly generations develops in one bird nesting season.

Table 1 A comparison between selected factors of living conditions of the avian vampire fly in its regions of origin in South America, as well as on the Galapagos · Regions of origin in South America · Galapagos Islands

Bird species infested by the avian vampire fly · numerous small passerines 2, including finches, cuckoos and woodpeckers · numerous small passerines, including almost all Darwin finch species and cuckoos

Percentage of nests infested by the avian vampire fly · less than 30 % · more than 90 %

Average number of larvae per nest · fewer than 10 · more than 30

Percentage of avian vampire fly larvae killed by parasitic wasps · 10 % to 20 % · max. 5 %

Predators of the avian vampire fly larvae · ants · none

1 Blutarmut

2 Sperlingsvögel

Material B: Effect of Permethrin on Nerve Cells

The infestation of avian vampire flies has led to a strong decline in the number of Darwin finches. The insecticide permethrin is used to control the avian vampire fly populations on the Galapagos Islands. Insects take up permethrin via their body surface. Treated insects die when a sufficiently high dose is applied, but they can recover if the applied dose is too low. Permethrin binds to voltage-gated sodium channels in the axon membrane. The neurophysiological effects of permethrin were investigated in experiments. For this purpose, insect nerve cells were treated with permethrin and briefly stimulated; the membrane potential was measured (Figure 1).

Material C: The Use of Permethrin to Protect Darwin Finches

The number of Darwin finches decreased significantly on the Galapagos Islands due to the infestation with avian vampire flies, as up to 95 % of the chicks die in the field. In order to protect the bird populations, control measures with the insecticide permethrin were investigated in field experiments.

In a first experiment, dispensers with cotton fibres were set up. The fibres were used by the finches to build their nests. The dispensers for the experiment contained cotton fibres treated with a 1% permethrin solution. The cotton fibres in the control dispensers were treated with water. After hatching, the mass of cotton used to build the nests as well as the number of avian vampire fly larvae were determined (Figure 2).

Nests were sprayed with a 1% permethrin solution or with water in a second field experiment. Then the number of fledged nestlings 3 from these nests were determined (Figure 3).

Another study investigated whether permethrin treatment has any long-term effects on Darwin finches. For this purpose, experiments were carried out in the laboratory with the closely related zebra finch species ( Taeniopygia guttata), as this species is easier to keep and breed than Darwin finches. Two generations of zebra finches were bred for the study. Either nesting material that had been treated with a 1% permethrin solution or with water was used for both generations. The eggs and hatchlings of both generations were investigated and the reproductive success determined.

In the first generation, no significant differences were observed between the control group and the group with nests that had been treated with permethrin. In the second generation there were no significant differences regarding the number of eggs and the number of hatched nestlings, but there were differences in the mortality of nestlings: whereas all nestlings survived in the control nests, 64% survived in the nests treated with permethrin.

3 flügge gewordene Jungvögel

3. Sum up the data given in Material C. Discuss whether it makes sense to protect Darwin finches from the avian vampire fly by providing cotton treated with permethrin (Materials A–C). [14 Punkte]

a)

b)

Material A: Ecology of Eurasian Shrews

The Eurasian water shrew 1 ( Neomys fodiens), the Mediterranean water shrew 2 ( Neomys anomalus) and the common shrew 3 ( Sorex araneus) all belong to the shrew family. All three species occur together in Europe and in parts of Asia.

The Eurasian water shrew is the largest of the three species. It has swimming bristles 4 on its hind feet and on its tail. It can swim and dive well. This nocturnal animal lives in thinner vegetation along the banks of fast-flowing rivers and streams. Swamps, wet forests and meadows are inhabited as well. The Mediterranean water shrew is also nocturnal and can also swim and dive. Its swimming bristles are shorter than those of the Eurasian water shrew and are sometimes missing entirely. It prefers to live on the banks of slower-flowing waters and in wetland areas with thick herb and bush growth. The diurnal and nocturnal common shrew occurs particularly in wet forests and meadows, but can also be found in other terrestrial habitats.

In addition to the invertebrates shown in Table 1, the Eurasian water shrew also preys upon smaller vertebrates such as frogs and fish. The common shrew occasionally eats small vertebrates such as frogs and young mice.

Table 1 Prey spectrum of the Eurasian water shrew, the Mediterranean water shrew and the common shrew. The faeces of captured shrews were analysed. The values show the percentage of shrews in which each prey animal type was found.

· Eurasian

water shrew · Mediterranean

water shrew · Common shrew

Terrestrial prey

Ground beetles · 22.6 % · 30.8 % · 6.3 %

Other beetles · 32.3 % · 38.5 % · 56.3 %

Beetle larvae · 6.5 % · 23.1 % · 31.3 %

Ants · 12.9 % · 0.0 % · 25.0 %

Millipedes · 61.3 % · 38.5 % · 3.1 %

Spiders · 74.2 % · 76.9 % · 63.3 %

Earthworms · 45.2 % · 100.0 % · 90.6 %

Aquatic prey

Caddisfly larvae 5 · 12.9 % · 15.4 %

Soldier fly larvae 6 · 6.5 % · 15.4 %

Asellus aquaticus 7 · 51.6 % · 23.1 %

1 Eurasische Wasserspitzmaus | 2 Sumpfspitzmaus | 3 Waldspitzmaus | 4 Schwimmborsten | 5 Köcherfliegenlarven | 6 Waffenfliegenlarven | 7 Wasserasseln

Material B: Prey Handling by Shrew Species

Shrews consume a large amount of food every day to meet their high energy requirements. As they are also active in the winter, they need food all year round. They often capture more prey than they consume directly; some of the prey animals are hoarded 8 for a while in their burrows 9. Some of these prey animals are bitten to immobilise them. This can be carried out mechanically by biting through nerves which innervate muscles. This immobilisation is also possible through the use of venoms.

The Eurasian water shrew and the Mediterranean water shrew produce a venom in glands under the tongue. The venom is transferred to the prey together with saliva and has a paralysing effect on the muscles. The common shrew, in contrast, is not venomous.

In a lab experiment, researchers investigated how the Eurasian water shrew and the smaller common shrew handle prey of different sizes and masses. The shrews were offered various prey animals: mealworms 10 were used as small, light prey, earthworms were used as medium-sized prey, and frogs as large, heavy prey. The proportions of the prey animals which were eaten either directly or little by little were determined, as were the proportions of prey animals which were either hoarded in the burrows or completely ignored (Figure 1A). Figure 1B shows the length of time needed to overpower the prey.

8 horten | 9 Bau | 10 Mehlkäferlarven

Material C: Relationships and Venomousness

The relationships between selected genera of shrew were determined based on molecular data; in a phylogenetic tree, these relationships are shown together with the occurrence of the trait 'venomousness' (Figure 2). The Eurasian water shrew and the Mediterranean water shrew both belong to the genus Neomys (Eurasian water shrews).

1. Summarise what Material A shows about the prey spectrum of the three shrew species. Analyse and evaluate Material A with regard to the ecological relationships and give reasons why the three shrew species are able to coexist (Material A). (14 Punkte)

Material A: Ecology of Eurasian Shrews

The Eurasian water shrew 1 ( Neomys fodiens), the Mediterranean water shrew 2 ( Neomys anomalus) and the common shrew 3 ( Sorex araneus) all belong to the shrew family. All three species occur together in Europe and in parts of Asia.

The Eurasian water shrew is the largest of the three species. It has swimming bristles 4 on its hind feet and on its tail. It can swim and dive well. This nocturnal animal lives in thinner vegetation along the banks of fast-flowing rivers and streams. Swamps, wet forests and meadows are inhabited as well. The Mediterranean water shrew is also nocturnal and can also swim and dive. Its swimming bristles are shorter than those of the Eurasian water shrew and are sometimes missing entirely. It prefers to live on the banks of slower-flowing waters and in wetland areas with thick herb and bush growth. The diurnal and nocturnal common shrew occurs particularly in wet forests and meadows, but can also be found in other terrestrial habitats.

In addition to the invertebrates shown in Table 1, the Eurasian water shrew also preys upon smaller vertebrates such as frogs and fish. The common shrew occasionally eats small vertebrates such as frogs and young mice.

Table 1 Prey spectrum of the Eurasian water shrew, the Mediterranean water shrew and the common shrew. The faeces of captured shrews were analysed. The values show the percentage of shrews in which each prey animal type was found.

· Eurasian

water shrew · Mediterranean

water shrew · Common shrew

Terrestrial prey

Ground beetles · 22.6 % · 30.8 % · 6.3 %

Other beetles · 32.3 % · 38.5 % · 56.3 %

Beetle larvae · 6.5 % · 23.1 % · 31.3 %

Ants · 12.9 % · 0.0 % · 25.0 %

Millipedes · 61.3 % · 38.5 % · 3.1 %

Spiders · 74.2 % · 76.9 % · 63.3 %

Earthworms · 45.2 % · 100.0 % · 90.6 %

Aquatic prey

Caddisfly larvae 5 · 12.9 % · 15.4 %

Soldier fly larvae 6 · 6.5 % · 15.4 %

Asellus aquaticus 7 · 51.6 % · 23.1 %

1 Eurasische Wasserspitzmaus | 2 Sumpfspitzmaus | 3 Waldspitzmaus | 4 Schwimmborsten | 5 Köcherfliegenlarven | 6 Waffenfliegenlarven | 7 Wasserasseln

Material B: Prey Handling by Shrew Species

Shrews consume a large amount of food every day to meet their high energy requirements. As they are also active in the winter, they need food all year round. They often capture more prey than they consume directly; some of the prey animals are hoarded 8 for a while in their burrows 9. Some of these prey animals are bitten to immobilise them. This can be carried out mechanically by biting through nerves which innervate muscles. This immobilisation is also possible through the use of venoms.

The Eurasian water shrew and the Mediterranean water shrew produce a venom in glands under the tongue. The venom is transferred to the prey together with saliva and has a paralysing effect on the muscles. The common shrew, in contrast, is not venomous.

In a lab experiment, researchers investigated how the Eurasian water shrew and the smaller common shrew handle prey of different sizes and masses. The shrews were offered various prey animals: mealworms 10 were used as small, light prey, earthworms were used as medium-sized prey, and frogs as large, heavy prey. The proportions of the prey animals which were eaten either directly or little by little were determined, as were the proportions of prey animals which were either hoarded in the burrows or completely ignored (Figure 1A). Figure 1B shows the length of time needed to overpower the prey.

8 horten | 9 Bau | 10 Mehlkäferlarven

Material C: Relationships and Venomousness

The relationships between selected genera of shrew were determined based on molecular data; in a phylogenetic tree, these relationships are shown together with the occurrence of the trait 'venomousness' (Figure 2). The Eurasian water shrew and the Mediterranean water shrew both belong to the genus Neomys (Eurasian water shrews).

2. Summarise the findings shown in Figure 1A and interpret how the two shrew species behave (Materials A and B). Drawing on the data in Figure 1B, put forward a well-reasoned hypothesis about the role of the venom for the Eurasian water shrew (Materials A and B).

[20 Punkte]

a)

b)

c)

Material A: Ecology of Eurasian Shrews

The Eurasian water shrew 1 ( Neomys fodiens), the Mediterranean water shrew 2 ( Neomys anomalus) and the common shrew 3 ( Sorex araneus) all belong to the shrew family. All three species occur together in Europe and in parts of Asia.

The Eurasian water shrew is the largest of the three species. It has swimming bristles 4 on its hind feet and on its tail. It can swim and dive well. This nocturnal animal lives in thinner vegetation along the banks of fast-flowing rivers and streams. Swamps, wet forests and meadows are inhabited as well. The Mediterranean water shrew is also nocturnal and can also swim and dive. Its swimming bristles are shorter than those of the Eurasian water shrew and are sometimes missing entirely. It prefers to live on the banks of slower-flowing waters and in wetland areas with thick herb and bush growth. The diurnal and nocturnal common shrew occurs particularly in wet forests and meadows, but can also be found in other terrestrial habitats.

In addition to the invertebrates shown in Table 1, the Eurasian water shrew also preys upon smaller vertebrates such as frogs and fish. The common shrew occasionally eats small vertebrates such as frogs and young mice.

Table 1 Prey spectrum of the Eurasian water shrew, the Mediterranean water shrew and the common shrew. The faeces of captured shrews were analysed. The values show the percentage of shrews in which each prey animal type was found.

· Eurasian

water shrew · Mediterranean

water shrew · Common shrew

Terrestrial prey

Ground beetles · 22.6 % · 30.8 % · 6.3 %

Other beetles · 32.3 % · 38.5 % · 56.3 %

Beetle larvae · 6.5 % · 23.1 % · 31.3 %

Ants · 12.9 % · 0.0 % · 25.0 %

Millipedes · 61.3 % · 38.5 % · 3.1 %

Spiders · 74.2 % · 76.9 % · 63.3 %

Earthworms · 45.2 % · 100.0 % · 90.6 %

Aquatic prey

Caddisfly larvae 5 · 12.9 % · 15.4 %

Soldier fly larvae 6 · 6.5 % · 15.4 %

Asellus aquaticus 7 · 51.6 % · 23.1 %

1 Eurasische Wasserspitzmaus | 2 Sumpfspitzmaus | 3 Waldspitzmaus | 4 Schwimmborsten | 5 Köcherfliegenlarven | 6 Waffenfliegenlarven | 7 Wasserasseln

Material B: Prey Handling by Shrew Species

Shrews consume a large amount of food every day to meet their high energy requirements. As they are also active in the winter, they need food all year round. They often capture more prey than they consume directly; some of the prey animals are hoarded 8 for a while in their burrows 9. Some of these prey animals are bitten to immobilise them. This can be carried out mechanically by biting through nerves which innervate muscles. This immobilisation is also possible through the use of venoms.

The Eurasian water shrew and the Mediterranean water shrew produce a venom in glands under the tongue. The venom is transferred to the prey together with saliva and has a paralysing effect on the muscles. The common shrew, in contrast, is not venomous.

In a lab experiment, researchers investigated how the Eurasian water shrew and the smaller common shrew handle prey of different sizes and masses. The shrews were offered various prey animals: mealworms 10 were used as small, light prey, earthworms were used as medium-sized prey, and frogs as large, heavy prey. The proportions of the prey animals which were eaten either directly or little by little were determined, as were the proportions of prey animals which were either hoarded in the burrows or completely ignored (Figure 1A). Figure 1B shows the length of time needed to overpower the prey.

8 horten | 9 Bau | 10 Mehlkäferlarven

Material C: Relationships and Venomousness

The relationships between selected genera of shrew were determined based on molecular data; in a phylogenetic tree, these relationships are shown together with the occurrence of the trait 'venomousness' (Figure 2). The Eurasian water shrew and the Mediterranean water shrew both belong to the genus Neomys (Eurasian water shrews).

3. Analyse the phylogenetic tree shown in Figure 2 with regard to the presence of venom in the listed genera (Materials B and C). Drawing on all the materials, develop a hypothesis about how the Eurasian water shrew and the Mediterranean water shrew evolved (Materials A–C).

[20 Punkte]

Material A: Ivermectin

Dogs can be infested with parasites, for example lice, mites or ticks. Substances such as ivermectin are used to fight these parasites. Ivermectin is a neurotoxin which is lethal particularly to invertebrates. It binds to glutamate-gated chloride ion channels in the postsynaptic membrane and opens them permanently. Glutamate-gated chloride ion channels are found only in invertebrates.

Ivermectin is less toxic to vertebrates and thus is used to treat dogs with parasitic infestations. Ivermectin is a fat-soluble substance, which can diffuse through the cell membrane. In animals treated with ivermectin, it accumulates in their livers and fat tissues and is slowly released from there. The substance then circulates in low amounts in the blood of the treated animals and is taken up by the parasites.

Material B: Ivermectin Sensitivity

In higher concentrations, ivermectin can also bind to GABA-gated chloride channels in vertebrates and activate them. This can cause neurotoxic effects, especially in the central nervous system of vertebrates.

After a treatment with ivermectin, symptoms such as movement disorders, cramps, lightheadedness 1 and even coma could often be observed in collies and other dog breeds. Since not all dogs of a breed are affected by ivermectin in the same way, the individual causes for this sensitivity were analysed.

A mutation in the MDR1 gene was identified as the cause of this sensitivity. Experiments with mice were carried out to understand the function of MDR1 in mammals. Researchers used wild-type mice and genetically modified mice whose MDR1 gene had been inactivated. After the treatment with ivermectin, its concentration in different tissues was measured in both groups (Table 1).

In mammals, the MDR1 gene codes for the transport protein MDR1. It uses ATP to transport foreign substances 2 out of the cells and back into the bloodstream, so that they can be removed. MDR1 also occurs in the cells of the blood vessel walls of the blood brain barrier. The blood brain barrier is selective and allows only certain substances from the blood to enter the brain. Thus, it creates a barrier between the central nervous system and the blood.

1 Benommenheit

2 hier: körperfremde Stoffe

Material C: MDR1 Mutations in Collies

The results of genetic analyses of the MDR1 gene in collies which are sensitive to ivermectin are shown in Table 2. The whole MDR1 protein is 1281 amino acids long.

Material D: Detection of the MDR1 Alleles

The mode of inheritance of ivermectin sensitivity is autosomal recessive. DNA samples of different dogs were analysed using polymerase chain reaction (PCR). The respective primer pairs as well as the expected sizes of the amplified fragments are shown in Figure 1. The results of a gel electrophoresis of the PCR products are shown in Figure 2.

Material E: Diagram and Codon Table of the Genetic Code

1. Describe what happens at an inhibitory chemical synapse and explain, on a molecular level, how ivermectin affects invertebrates (Material A). (12 Punkte)

Material A: Ivermectin

Dogs can be infested with parasites, for example lice, mites or ticks. Substances such as ivermectin are used to fight these parasites. Ivermectin is a neurotoxin which is lethal particularly to invertebrates. It binds to glutamate-gated chloride ion channels in the postsynaptic membrane and opens them permanently. Glutamate-gated chloride ion channels are found only in invertebrates.

Ivermectin is less toxic to vertebrates and thus is used to treat dogs with parasitic infestations. Ivermectin is a fat-soluble substance, which can diffuse through the cell membrane. In animals treated with ivermectin, it accumulates in their livers and fat tissues and is slowly released from there. The substance then circulates in low amounts in the blood of the treated animals and is taken up by the parasites.

Material B: Ivermectin Sensitivity

In higher concentrations, ivermectin can also bind to GABA-gated chloride channels in vertebrates and activate them. This can cause neurotoxic effects, especially in the central nervous system of vertebrates.

After a treatment with ivermectin, symptoms such as movement disorders, cramps, lightheadedness 1 and even coma could often be observed in collies and other dog breeds. Since not all dogs of a breed are affected by ivermectin in the same way, the individual causes for this sensitivity were analysed.

A mutation in the MDR1 gene was identified as the cause of this sensitivity. Experiments with mice were carried out to understand the function of MDR1 in mammals. Researchers used wild-type mice and genetically modified mice whose MDR1 gene had been inactivated. After the treatment with ivermectin, its concentration in different tissues was measured in both groups (Table 1).

In mammals, the MDR1 gene codes for the transport protein MDR1. It uses ATP to transport foreign substances 2 out of the cells and back into the bloodstream, so that they can be removed. MDR1 also occurs in the cells of the blood vessel walls of the blood brain barrier. The blood brain barrier is selective and allows only certain substances from the blood to enter the brain. Thus, it creates a barrier between the central nervous system and the blood.

1 Benommenheit

2 hier: körperfremde Stoffe

Material C: MDR1 Mutations in Collies

The results of genetic analyses of the MDR1 gene in collies which are sensitive to ivermectin are shown in Table 2. The whole MDR1 protein is 1281 amino acids long.

Material D: Detection of the MDR1 Alleles

The mode of inheritance of ivermectin sensitivity is autosomal recessive. DNA samples of different dogs were analysed using polymerase chain reaction (PCR). The respective primer pairs as well as the expected sizes of the amplified fragments are shown in Figure 1. The results of a gel electrophoresis of the PCR products are shown in Figure 2.

Material E: Diagram and Codon Table of the Genetic Code

2. Compare how ivermectin is distributed across various mouse tissues (Table 1) and deduce which function the MDR1 protein performs in mammals (Materials A and B). Work out the amino acid sequences encoded by the DNA sequences given in Table 2 and determine the type of mutation involved (Materials C and E). Illustrate how the MDR1 protein and the affected dogs are impacted (Materials A–C). [24 Punkte]

a)

b)

Determine the amino acid sequences of both alleles (triplets 73 to 81) in the 3-letter code (separated by hyphens, e.g. Gly-Asn-...) and identify the type of mutation:

c)

Material A: Ivermectin

Dogs can be infested with parasites, for example lice, mites or ticks. Substances such as ivermectin are used to fight these parasites. Ivermectin is a neurotoxin which is lethal particularly to invertebrates. It binds to glutamate-gated chloride ion channels in the postsynaptic membrane and opens them permanently. Glutamate-gated chloride ion channels are found only in invertebrates.

Ivermectin is less toxic to vertebrates and thus is used to treat dogs with parasitic infestations. Ivermectin is a fat-soluble substance, which can diffuse through the cell membrane. In animals treated with ivermectin, it accumulates in their livers and fat tissues and is slowly released from there. The substance then circulates in low amounts in the blood of the treated animals and is taken up by the parasites.

Material B: Ivermectin Sensitivity

In higher concentrations, ivermectin can also bind to GABA-gated chloride channels in vertebrates and activate them. This can cause neurotoxic effects, especially in the central nervous system of vertebrates.

After a treatment with ivermectin, symptoms such as movement disorders, cramps, lightheadedness 1 and even coma could often be observed in collies and other dog breeds. Since not all dogs of a breed are affected by ivermectin in the same way, the individual causes for this sensitivity were analysed.

A mutation in the MDR1 gene was identified as the cause of this sensitivity. Experiments with mice were carried out to understand the function of MDR1 in mammals. Researchers used wild-type mice and genetically modified mice whose MDR1 gene had been inactivated. After the treatment with ivermectin, its concentration in different tissues was measured in both groups (Table 1).

In mammals, the MDR1 gene codes for the transport protein MDR1. It uses ATP to transport foreign substances 2 out of the cells and back into the bloodstream, so that they can be removed. MDR1 also occurs in the cells of the blood vessel walls of the blood brain barrier. The blood brain barrier is selective and allows only certain substances from the blood to enter the brain. Thus, it creates a barrier between the central nervous system and the blood.

1 Benommenheit

2 hier: körperfremde Stoffe

Material C: MDR1 Mutations in Collies

The results of genetic analyses of the MDR1 gene in collies which are sensitive to ivermectin are shown in Table 2. The whole MDR1 protein is 1281 amino acids long.

Material D: Detection of the MDR1 Alleles

The mode of inheritance of ivermectin sensitivity is autosomal recessive. DNA samples of different dogs were analysed using polymerase chain reaction (PCR). The respective primer pairs as well as the expected sizes of the amplified fragments are shown in Figure 1. The results of a gel electrophoresis of the PCR products are shown in Figure 2.

Material E: Diagram and Codon Table of the Genetic Code

3. Outline the basic stages of the polymerase chain reaction (PCR) and explain what role the primers play in the diagnostic procedure presented (Figure 1, Materials C and D). Analyse and evaluate Figure 2 regarding the genotypes of the dogs that were tested (Material D). Illustrate what consequences may result for dog breeding (Materials A–D). [18 Punkte]

a)

Outline the basic stages of the polymerase chain reaction (PCR):

b)

Explain what role the primers play in the diagnostic procedure presented (Figure 1, Materials C and D):

c)

Analyse and evaluate Figure 2 in order to establish the genotypes of the dogs tested:

Dog · Wild-type band (341 bp) · Mutant band (577 bp) · Genotype

Dog 1 · No · Yes (~577 bp)

Dog 2 · Yes (~341 bp) · Yes (~577 bp)

Dog 3 · Yes (~341 bp) · Yes (~577 bp)

Dog 4 · Yes (~341 bp) · No

d)

Illustrate what consequences may result for dog breeding (Materials A–D):