17. Selection and evolution
A section of Biology, 9700
Listing 10 of 104 questions
Complete the following paragraphs using the most appropriate word or words. The theory of evolution describes a process that can lead to the formation of new species from pre-existing species over . DNA sequence data of different species can be compared to show evolutionary relationships. Two species that have a more recent common ancestor share more in the DNA nucleotide sequences of their genomes than two species that are more distantly related. Mitochondrial DNA can also be used in the study of evolutionary relationships. Mitochondrial DNA is inherited only from the female gamete, and its nucleotide sequence is unaffected by during the production of gametes. DNA sequence data can be stored in large biological , allowing faster comparison of the nucleotide sequences of genomes using computer software. DNA sequence data can also be used to predict the sequences of proteins produced by a species. A can be used to detect many different mRNA molecules at the same time in studies that compare gene expression between different species.
9700_m24_qp_42
THEORY
2024
Paper 4, Variant 2
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Anole lizards are found throughout the Caribbean and the surrounding mainland. There are many species. Each species is found only on one island or a small group of islands, apart from Anolis carolinensis which is found in mainland Florida. shows the distribution of four species of anole lizards. Florida U.S.A. Cuba Andros Acklins Anolis smaragdinus Anolis brunneus Anolis carolinensis Anolis porcatus 50 100 km An investigation was carried out into the relationships between these four lizard species, using DNA analysis. The base sequences of a region of mitochondrial DNA from the four species were compared. The results are shown in Table 5.1. The smaller the number, the smaller the differences between the base sequences of the two species. Table 5.1 A. brunneus A. brunneus A. smaragdinus A. smaragdinus 12.1 A. carolinensis A. carolinensis 16.7 15.0 A. porcatus A. porcatus 11.3 8.9 13.2 With reference to Table 5.1, state the species to which A. brunneus appears to be most closely related. The researchers put forward the hypothesis that the three species, A. brunneus, A. smaragdinus and A. carolinensis, have originated from three separate events in which a few individuals of A. porcatus spread directly from Cuba to three different places. Explain how the results in Table 5.1 support the researchers’ hypothesis. Explain how a population of A. porcatus that became isolated on an island could evolve into a new species.
9700_s10_qp_41
THEORY
2010
Paper 4, Variant 1
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Collared lizards, Crotaphytus collaris, show variation in body length and running speed. shows a collared lizard. An investigation was carried out to find out whether body length and running speed affected the number of offspring that a male lizard sired . The lizards reproduce sexually, and females lay eggs after mating with males. A large number of male lizards was captured during the breeding season. For each lizard: • body length was measured • it was chased down a small race track and its fastest running speed over 1 m recorded • a blood sample was taken and DNA sequences at 10 different loci were analysed. The lizards were then released back into the place where they were captured, to allow mating to occur. 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 determine which male was the father. The results were used to determine the number of offspring sired by each of the male lizards in the first sample. Outline how DNA analysis can be carried out and then used to establish which male lizard sired each hatchling. shows the number of offspring sired plotted against the body length of the adult male lizards. shows the number of offspring sired plotted against the fastest running speed (sprint speed) of the adult male lizards. number of offspring sired 2.00 2.01 2.02 2.03 2.04 2.05 2.06 body length (log scale) number of offspring sired 0.40 0.45 0.50 0.55 0.60 0.65 0.70 sprint speed (log scale) With reference to and , describe the relationships between • body length and the number of offspring produced • sprint speed and the number of offspring produced. body length sprint speed Research has also shown that, in a population of collared lizards with varying leg lengths, those with longer hind legs are able to run faster. With reference to the results shown in , explain how, over time, this could lead to a change in the mean hind leg length in a population of collared lizards. Small islands often contain species of lizards that are not found on other islands or on the mainland. Explain how a population of collared lizards that became isolated on an island could evolve to form a new species.
9700_s14_qp_42
THEORY
2014
Paper 4, Variant 2
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State the general theory of evolution. Different types of organism have evolved different structures containing light receptors. Eyes are organs containing light receptors. describes the light receptors of several types of organism. Euglena (a single-celled eukaryote) has a simple eyespot that can only detect the intensity and direction of light. Turbellarian flatworms have cup-shaped eyes, each with a layer of light receptor cells. They can detect the intensity and direction of light better than Euglena. They also detect movement. The mollusc Nautilus has eyes with deeper cups and narrower openings for light to enter. They can form a rough image, see shapes and detect the direction of light better than turbellarian flatworms. The mollusc Nucella has eyes with lenses made of jelly. They can form a more detailed image than the eyes of Nautilus and can focus light to a small degree. Mammals have eyes that are more complex than Nucella. They have a fixed lens (the cornea) that bends light and a lens that can change shape to focus on objects at different distances. The lenses focus light onto a deeply cup-shaped layer of light receptor cells. The eyes form a very detailed image. Using the information in , suggest how a complex eye such as that of mammals could have evolved in successive stages. Octopuses are molluscs that have eyes very similar to those of mammals. Octopuses and mammals are not closely related. Octopuses and mammals have lenses that can change shape to focus on objects at different distances. Suggest reasons why octopuses and mammals have evolved similar eye structures. Molecular evidence is used to investigate evolution. One study involved a marine worm, Platynereis dumerilii, that still has characteristics similar to its ancestors from 600 million years ago. Researchers sequenced all the proteins in light receptor cells of P. dumerilii and humans. The results showed that there are many similarities between the protein sequences of P. dumerilii and humans, particularly in the light-detecting protein opsin. State what this molecular evidence indicates about the evolutionary origins of P. dumerilii and humans. Explain how amino acid sequences indicate how close the relationship is between two species.
9700_s19_qp_42
THEORY
2019
Paper 4, Variant 2
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Cats are members of the Felidae family. Two genera of Felidae are Leopardus and Panthera. The genus Leopardus consists of species of wild cats that are small and spotted. In 2013, biologists investigated the evolution of Leopardus tigrinus in South America. shows the locations in South America of two populations of. L. tigrinus, population A and population B. population A population B • Population A lives in grassland and desert habitats and population B lives in forest habitats. • The cats in population A have a lighter coat colour and a different pattern of spots from the cats in population B. • Genetic analysis shows that population A is genetically distinct from population B. • Population B has now been reclassified as a new species, L. guttulus. Define the term species. Explain how the two species, L. tigrinus and L. guttulus, have evolved from one original population in South America. Illegal trade threatens the survival of endangered species. Forensic tests can identify animal species from the DNA of their body parts, for example bones. Cat species differ in the number of repeats of bases C and A (CA repeats) within one particular region of DNA, known as Ple46. Table 3.1 shows the number of repeats in Ple46 for three endangered cat species. Table 3.1 cat species number of CA repeats in Ple46 Asiatic lion Bengal tiger 7–8 leopard 14–15 Gel electrophoresis is used to estimate the length of Ple46 in a sample of DNA to check whether the sample comes from one of the endangered cat species in Table 3.1. Outline how gel electrophoresis is carried out to confirm whether the sample comes from one of these endangered cat species. Customs officials are responsible for checking whether animal body parts come from species on the CITES list of endangered species. Officials can now use a small DNA barcoding kit linked to a computer database to identify a species. Suggest two advantages of using this method to identify a species.
9700_s20_qp_41
THEORY
2020
Paper 4, Variant 1
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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 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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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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Russian scientists have discovered the fruits of a flowering plant, Silene stenophylla, in the food store in a burrow of a ground squirrel in frozen sediments in Siberia. Dating techniques suggest that the fruits were stored by the ground squirrel about 32 000 years ago, shortly before the ground became permanently frozen. Tissue samples were taken from the fruits and grown in a nutrient culture medium. After treatment with plant hormones to stimulate the growth of roots and shoots, 36 complete plants were produced. These ‘regenerated’ plants, which looked identical to one another, flowered and after cross-pollination, produced seeds that were able to germinate. Explain why cross-pollination produces more genetic variation among the offspring than self-pollination. The flowers of modern-day S. stenophylla look similar, but not identical, to the flowers of the ‘regenerated’ plants. Outline how DNA sequencing could be used to compare the DNA of modern-day and ‘regenerated’ S. stenophylla. Suggest a simple experiment, using plants of modern-day and ‘regenerated’ S. stenophylla to find out whether, after 32 000 years, they are still the same species.
9700_s14_qp_41
THEORY
2014
Paper 4, Variant 1
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Questions Discovered
104