17.3. Evolution
A subsection of Biology, 9700, through 17. Selection and evolution
Listing 10 of 28 questions
A subspecies is a genetically distinct population within a species that has some phenotypic differences from the rest of the species, but is not yet reproductively isolated. Nine subspecies of the tiger, Panthera tigris, have been identified. Six of these subspecies are found on mainland Asia. Three of the subspecies originate from the Sunda Islands. These islands include Bali, Java and the large island of Sumatra. shows these three islands. Sumatra Java Bali Sumatra Java Bali • The Bali tiger, Panthera tigris balica (P. t. balica), became extinct in the 20th Century. The Bali tiger was found only on the island of Bali. • The Javan tiger, P. t. sondaica, became extinct in the 20th Century. The Javan tiger was found only on the island of Java. • The Sumatran tiger, P. t. sumatrae, lives only on Sumatra and is the closest living relative of Bali and Javan tigers. 20 000 years ago land bridges temporarily connected the Sunda Islands. A recent study carried out a genetic analysis of the nine subspecies of tiger. Specific sections of mitochondrial DNA (mtDNA) that are useful in studies of evolution were amplified using PCR and compared to assess their evolutionary history. • The source of DNA for the extinct subspecies came from museum specimens. • mtDNA was extracted and polymerase chain reaction (PCR) carried out using primers based on specific sections of tiger mtDNA. • The mtDNA sections for the three island subspecies were genetically distinct from the other six mainland subspecies. • The mtDNA sections for the three island subspecies were all found to be very similar. Suggest and explain how the three subspecies of tiger on the Sunda Islands formed. Explain why specific primers were used for the tiger mtDNA sections. Describe and explain one characteristic of mtDNA that makes it more useful than using nuclear DNA to provide evidence of evolution. Suggest two reasons why P. t. balica and P. t. sondaica became extinct. Suggest why P. t. sumatrae is still considered to be a member of the species Panthera tigris.
9700_s20_qp_42
THEORY
2020
Paper 4, Variant 2
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The collared flycatcher, Ficedula albicollis, and the pied flycatcher, F. hypoleuca are two closely related species of bird. DNA analysis has shown that speciation from a common ancestor occurred approximately 1 million years ago. A study was carried out on the island of Öland, Sweden. In Öland, the breeding areas of the two bird species overlap and small numbers of hybrid flycatchers are produced. • Birds were captured and their DNA was analysed to identify whether each bird was F. albicollis, F. hypoleuca or a hybrid. • Sperm samples were taken from the male birds. Table 3.1 shows the percentage of males of each bird type with normal sperm. Table 3.1 bird type percentage of males with normal sperm F. albicollis F. hypoleuca male hybrid • The researchers observed that female birds mostly choose mates of their own species based on plumage and song. • Hybrid flycatchers are produced when female F. albicollis mate with male F. hypoleuca that have a song that is similar to F. albicollis. • Analysis showed that all female hybrids were sterile. The group of eggs a female bird lays at a single time in its nest is called a clutch. The offspring in the nest are looked after by a male-female pair. Sometimes the male in the male-female pair does not provide the sperm that fertilise the eggs of the female. Table 3.2 shows: • the percentage of clutches with eggs that hatched • the percentage of extra-pair nestlings (offspring in the nest fathered by a male that was different from the male of the male-female pair). Table 3.2 parents of nest percentage of clutches with eggs that hatched percentage of extra-pair nestlings male female F. albicollis F. albicollis 94.5 17.2 F. hypoleuca F. hypoleuca 89.3 22.4 hybrid F. albicollis or F. hypoleuca 38.0 100.0 Discuss the pre-zygotic and post-zygotic isolating mechanisms that maintain F. albicollis and F. hypoleuca as separate species. Explain how the two species F. albicollis and F. hypoleuca could have evolved from one original ancestral population. A single-nucleotide polymorphism (SNP) is caused by a base pair substitution mutation in a specific region of DNA. One method of identifying whether two individuals have the same SNP is to: • use a specific primer and polymerase chain reaction (PCR) • add a restriction enzyme • carry out gel electrophoresis • stain with a dye to compare banding patterns. Explain why: a specific primer is used a restriction enzyme is added gel electrophoresis is carried out. The method of identifying whether two individuals have the same SNP method was carried out to compare species A and species B. shows the banding patterns that were observed. A species B well well Describe and suggest an explanation for the results obtained in .
9700_s20_qp_43
THEORY
2020
Paper 4, Variant 3
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Use A recent study of the house mouse, Mus musculus, on the island of Madeira resulted in the following observations. ● There are six distinct populations. ● The mice are associated with human settlements. ● The populations are located in different valleys separated by steep mountains. ● Each population has a different diploid number of chromosomes. As a result of these observations it has been suggested that speciation is taking place. is a map of Madeira showing the distribution of the six populations. mountains Using the information in , state the likely isolating mechanism and the type of speciation taking place. isolating mechanism type of speciation Examiner’s Use Explain how speciation is occurring in the house mouse populations of Madeira.
9700_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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The evolutionary origin of the four-legged amphibians (such as frogs and toads) from fish has been the subject of much debate for many years. Among living fish, the rarely-caught coelacanth and the lungfish are thought to be most closely related to these amphibians. Samples of blood were taken from two coelacanths that were captured recently near Comoros. The amino acid sequences of the α and β chains of coelacanth and lungfish haemoglobin were compared with the known sequences of amphibian adults and their aquatic larvae . Organisms with more matches in the amino acid sequence of a polypeptide chain share a more recent common ancestor than those with fewer matches. The comparisons with three species of amphibians, Xenopus laevis (Xl), X. tropicana (Xt) and Rana catesbeiana (Rc) are shown in Table 2.1. Table 2.1 percentage of matches of amino acid sequence species of amphibian adults species of amphibian larvae fish species Xl Xt Rc Xl Xt Rc α chains coelacanth 42.0 47.5 no data 45.4 42.6 48.2 lungfish 40.4 42.1 no data 40.7 39.0 37.9 β chains coelacanth 42.1 43.2 40.7 52.1 52.1 58.2 lungfish 44.1 45.9 41.4 47.3 45.9 48.6 Explain whether or not the information in Table 2.1 supports the suggestion that coelacanths and amphibians share a more recent common ancestor than do lungfish and amphibians. Suggest why adults and tadpoles of the same species of amphibian have different amino acid sequences in their haemoglobin. Coelacanth haemoglobin has a very high affinity for oxygen, suggesting that coelacanths, which have been captured at depths of between 200 m and 400 m, live in water that has a low concentration of oxygen. Explain how an environmental factor, such as the low concentration of oxygen in deep water, can act: as a stabilising force in natural selection as an evolutionary force in natural selection. Explain the role of isolating mechanisms in the evolution of new species.
9700_w13_qp_43
THEORY
2013
Paper 4, Variant 3
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All modern breeds of dog belong to the same species and are thought to have originated from 14 ancient breeds by the process of artificial selection. The golden retriever is a modern breed that is often used as a guide dog for people who are blind or visually impaired. shows a golden retriever. Explain how the principles of artificial selection would have been used to produce golden retrievers with the characteristics required for a guide dog. The domestic dog, Canis familiaris, is found worldwide. It is able to breed with all other members of the genus to form fertile hybrids. The distribution of some of the species belonging to the genus Canis is shown in . The dingo and the grey wolf species have distinct ranges but the ranges of three species of jackal overlap in East Africa. grey wolf dingo golden jackal side-striped jackal black-backed jackal Table 1.1 shows whether members of different species of the genus Canis are able to breed with each other. Table 1.1 key: ✓ = able to interbreed ✗ = unable to interbreed ? = interbreeding unknown dingo grey wolf golden jackal side- striped jackal black- backed jackal domestic dog dingo ✓ ? ? ? ? ✓ grey wolf ? ✓ ? ? ? ✓ golden jackal ? ? ✓ ✗ ✗ ✓ side-striped jackal ? ? ✗ ✓ ✗ ✓ black-backed jackal ? ? ✗ ✗ ✓ ✓ domestic dog ✓ ✓ ✓ ✓ ✓ ✓ Suggest the type of isolating mechanism preventing: • the three species of jackal interbreeding • the dingo mating with all the other members of the genus Canis apart from the domestic dog. Using the information in and Table 1.1, state: • one reason why the members of the genus Canis could be described as one species • one reason why they should be described as separate species.
9700_w14_qp_41
THEORY
2014
Paper 4, Variant 1
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All modern breeds of dog belong to the same species and are thought to have originated from 14 ancient breeds by the process of artificial selection. The golden retriever is a modern breed that is often used as a guide dog for people who are blind or visually impaired. shows a golden retriever. Explain how the principles of artificial selection would have been used to produce golden retrievers with the characteristics required for a guide dog. The domestic dog, Canis familiaris, is found worldwide. It is able to breed with all other members of the genus to form fertile hybrids. The distribution of some of the species belonging to the genus Canis is shown in . The dingo and the grey wolf species have distinct ranges but the ranges of three species of jackal overlap in East Africa. grey wolf dingo golden jackal side-striped jackal black-backed jackal Table 1.1 shows whether members of different species of the genus Canis are able to breed with each other. Table 1.1 key: ✓ = able to interbreed ✗ = unable to interbreed ? = interbreeding unknown dingo grey wolf golden jackal side- striped jackal black- backed jackal domestic dog dingo ✓ ? ? ? ? ✓ grey wolf ? ✓ ? ? ? ✓ golden jackal ? ? ✓ ✗ ✗ ✓ side-striped jackal ? ? ✗ ✓ ✗ ✓ black-backed jackal ? ? ✗ ✗ ✓ ✓ domestic dog ✓ ✓ ✓ ✓ ✓ ✓ Suggest the type of isolating mechanism preventing: • the three species of jackal interbreeding • the dingo mating with all the other members of the genus Canis apart from the domestic dog. Using the information in and Table 1.1, state: • one reason why the members of the genus Canis could be described as one species • one reason why they should be described as separate species.
9700_w14_qp_42
THEORY
2014
Paper 4, Variant 2
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A subspecies is a genetically distinct population of a species that has some phenotypic differences but is not yet reproductively isolated. 500 000 years ago, the European house mouse, Mus musculus, evolved into two subspecies, Mus musculus domesticus and Mus musculus musculus. Suggest and explain how the two subspecies M. m. domesticus and M. m. musculus could have evolved from the original M. musculus population. Today, M. m. domesticus populations are separated from M. m. musculus populations by a large hybrid zone. The hybrid zone formed 5000–1000 years ago when populations of the two subspecies overlapped and interbreeding occurred between the two subspecies, resulting in hybrids. Researchers investigated the populations in the hybrid zone. It was observed that: • hybrid mice were infected by more intestinal worms than M. m. domesticus and M. m. musculus • M. m. domesticus and M. m. musculus individuals frequently mate together • hybrid male mice had a very low fertility score based on testis weight and total sperm production, whereas M. m. domesticus and M. m. musculus males had a very high fertility score • some female hybrids were sterile • crosses between a fertile female hybrid and a male from either subspecies produced a very low number of offspring. M. m. domesticus and M. m. musculus usually have the same diploid number (2n = 40). Some individuals of M. m. domesticus have a different diploid number (2n = 34). Discuss the extent to which pre-zygotic and post-zygotic isolating mechanisms maintain M. m. domesticus and M. m. musculus as two separate subspecies within the hybrid zone.
9700_w20_qp_42
THEORY
2020
Paper 4, Variant 2
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Myosotis is a genus of small flowering plants. Many different Myosotis species grow on the islands of New Zealand, which are an important site of Myosotis evolution. Lowland Myosotis species grow at low altitude while alpine Myosotis species grow at high altitude at the tops of mountains. Scientists wanted to obtain molecular data to determine the evolutionary relationships of New Zealand’s Myosotis species. They extracted DNA from individuals of Myosotis species collected from three different islands in New Zealand. To carry out a polymerase chain reaction before DNA sequencing, the DNA samples were mixed with primers, deoxynucleotides and Taq polymerase and put through 35 cycles of treatment. Each treatment cycle involved one minute at 95 °C, followed by one minute at 50 °C and then four minutes at 72 °C. Describe what happened to the DNA at each temperature. shows the three largest New Zealand islands. North Island South Island Stewart Island km North Island has mostly lowland habitat. South Island and Stewart Island have mountains with alpine habitats that are above the tree line. DNA sequence data for three Myosotis species were compared. The results are described in the bullet points. • In the alpine species M. pygmaea, individuals on South Island showed genetic differences from individuals of M. pygmaea on Stewart Island. • In the alpine species M. pulvinaris, individuals from different mountains on South Island showed genetic differences. • In the lowland species M. pottsiana, individuals from different areas of North Island showed overall genetic similarity. Discuss reasons for the results in the three species. State two factors, other than natural selection, that could drive genetic changes in populations of Myosotis.
9700_w22_qp_42
THEORY
2022
Paper 4, Variant 2
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Spea multiplicata is one of several species of American spadefoot toad. Young spadefoot toads are called tadpoles and live in water in ponds. S. multiplicata tadpoles show three different phenotypes due to genetic variation. The three phenotypes are: detritus feeder, intermediate and carnivore. Detritus feeders are small, and carnivores are large. Intermediates vary in size between the two extremes. A detritus feeder and a carnivore are shown in . carnivore detritus feeder fairy shrimp Detritus feeders: • eat detritus (small pieces of dead organic matter) and algae (photosynthetic protoctists) • have smooth mouthparts, small jaw muscles and long intestines. Intermediates: • can eat all available food (detritus, algae and fairy shrimps) • have teeth‑like mouthparts, medium‑sized jaw muscles and medium‑sized intestines. Carnivores: • eat fairy shrimps and other small animals • have teeth‑like mouthparts, large jaw muscles and short intestines. Scientists counted the number of each type of tadpole in two different ponds: pond 1 and pond 2. In pond 1, the scientists observed: • a high density of tadpoles • a low abundance of food • that most of the tadpoles they counted were either detritus feeders or carnivores, with very few intermediates present. Describe and suggest explanations for the type of natural selection that appears to be acting in pond 1. In pond 2, the scientists observed: • a low density of tadpoles • sufficient food availability for all tadpoles • that most of the tadpoles they counted were intermediates, with fewer detritus feeders or carnivores. Describe and suggest explanations for the type of natural selection that appears to be acting in pond 2. The intestine length of S. multiplicata tadpoles shows continuous variation. Sketch a curve on to show how intestine length varies in the tadpole population in pond 2. length of intestine number of tadpoles A student suggested that the variation in S. multiplicata tadpoles could lead to sympatric speciation in some populations. Outline the features of sympatric speciation. shows the evolutionary relationships between three species of American spadefoot toad. Spea multiplicata Spea hammondii Spea bombifrons time / millions of years ago Explain how analysis of DNA allowed the evolutionary relationships shown in to be determined.
9700_w24_qp_41
THEORY
2024
Paper 4, Variant 1
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Questions Discovered
28