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Isolation Bio3B. Isolation Isolation prevents gene flow, thus reducing the inflow of alleles selected against – this intensifies the effect of natural.

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Presentation on theme: "Isolation Bio3B. Isolation Isolation prevents gene flow, thus reducing the inflow of alleles selected against – this intensifies the effect of natural."— Presentation transcript:

1 Isolation Bio3B

2 Isolation Isolation prevents gene flow, thus reducing the inflow of alleles selected against – this intensifies the effect of natural selection Barriers include: Geographical – rivers, oceans, mountains, deserts, etc

3 Isolation Reproductive – features that prevent interbreeding Mechanical – physical or anatomical differences that prevent mating eg different copulatory organs Behavioural – different mating calls or dances Ecological – different breeding locations, mating seasons Hybrid sterility – either no offspring are produced, or offspring are sterile

4 Migration Migration includes immigration coming in to a population emigration leaving a population Migration into new areas allows organisms to be subjected to a new set of selection pressures, and hence a new round of evolution In some cases, organisms unsuited to an environment can emigrate, thus increasing the effects of natural selection In other cases, organisms unsuited to an environment can immigrate, thus decreasing the effects of natural selection

5 Natural selection Once upon a time, on an island off the North-West coast of Europe, there lived a small frog called Crinea rotunda. This animal was similar to a tree frog but was spherical in shape. It lived all over the island. Early settlers divided the island in half by erecting a fence that snakes could not cross. Today, visitors to the island will only fin C. rotunda on the western side. On the eastern side there is a similar animal except it is not spherical, as it has more “normal” frog shape. Breeding experiments between the two types of frogs have resulted in no fertile offspring being produced. Using this information, and the map below, explain the likely steps that must have happened for this situation to have occurred. Include gene frequencies, isolating mechanisms, natural selection etc. Swamps – 2 monthsSwamps and lakes – 9 months Snakes No snakes

6 Natural selection Once upon a time, on an island off the North-West coast of Europe, there lived a small frog called Crinea rotunda. This animal was similar to a tree frog but was spherical in shape. It lived all over the island. Early settlers divided the island in half by erecting a fence that snakes could not cross. Today, visitors to the island will only fin C. rotunda on the western side. On the eastern side there is a similar animal except it is not spherical, as it has more “normal” frog shape. Breeding experiments between the two types of frogs have resulted in no fertile offspring being produced. Using this information, and the map below, explain the likely steps that must have happened for this situation to have occurred. Include gene frequencies, isolating mechanisms, natural selection etc. Swamps – 2 months Swamps and lakes – 9 months Snakes No snakes Variation must have existed in original population – spherical & normal shape Spherical variation gives advantage under certain conditions (eg drying out/predation by snakes Before separation selection pressures favour spherical shape over the entire island Fence acts as geographical barrier  isolation of 2 populations Each side now has different selection pressures On western side – selection pressures (snakes or drying out) favour spherical shape On eastern side there is more water & human presence - so no snakes & possibly different food/pollution effects – so spherical shape is not selected for Over time, the gene frequencies change – western side has larger frequency of spherical shape, eastern side has larger frequency or spherical shape After sufficient time populations no longer capable of interbreeding  new species has arisen

7 The widespread use and misuse of antibiotics has resulted in increased microbial resistance to antibiotics in clinical use, to the point that the methicillin-resistant Staphylococcus aureus (MRSA) has been described as a 'superbug' because of the threat it poses to health and its relative invulnerability to existing drugs. Describe how selection pressures have led to the new strain of Staphylococcus aureus and what can be done to reduce the selection pressures. methicillin-resistant Staphylococcus aureussuperbug

8 The widespread use and misuse of antibiotics has resulted in increased microbial resistance to antibiotics in clinical use, to the point that the methicillin-resistant Staphylococcus aureus (MRSA) has been described as a 'superbug' because of the threat it poses to health and its relative invulnerability to existing drugs. Describe how selection pressures have led to the new strain of Staphylococcus aureus and what can be done to reduce the selection pressures. methicillin-resistant Staphylococcus aureussuperbug Bacteria evolve to become the new resistant MRSA strain by natural selection this involves: Having genetically based variation within the population. (1 mark) Introduction of variation through mutation. (1 mark) Competition between variants. (1 marks) Selective pressures from the environment, especially the antibiotic. (1 marks) Different rates of survival, especially those that are MRSA.(1 mark) Inheritance of favourable resistant genes. (1 marks) Changes in allele frequencies. (1mark) Reducing the selection pressures Misuse of antibiotics. (1 mark) Failure to complete the course.(1 mark) Slow population growth reducing temperature. (1 mark) Reduce cross contamination. (1 mark)

9 The asexual, all-female whiptail species Cnemidophorus neomexicanus (centre), which reproduces via parthenogenesis, is shown flanked by two sexual species having males, C. inornatus (left) and C. tigris (right), which hybridized naturally to form the C. neomexicanus species. Cnemidophorus neomexicanusC. inornatusC. tigris Describe the advantages and disadvantages of each type of reproduction and how each type of reproduction is suited to the demands of living in a different type of environment

10 The asexual, all-female whiptail species Cnemidophorus neomexicanus (centre), which reproduces via parthenogenesis, is shown flanked by two sexual species having males, C. inornatus (left) and C. tigris (right), which hybridized naturally to form the C neomexicanus species.Cnemidophorus neomexicanusC. inornatusC. tigrisC neomexicanus Describe the advantages and disadvantages of each type of reproduction and how each type of reproduction is suited to the demands of living in a different type of environment. Sexual Reproduction Advantages (1 mark each, max 2 marks) Far more variation / Chance combination of gametes; they randomly join / Both sexes as offspring. Disadvantages (1 mark each, max 2 marks) Slow method of reproduction / Needs two parents one of each sex to come together Parthenogenesis asexual reproduction Advantages (1 mark each, max 2 marks) Offspring identical to the parent / Fast method of reproduction / Fast colonization by promoting organisms which are well adapted / Only one parent is needed. Disadvantages (1 mark each, max 2 marks) Disease could wipe out the whole population as no variation / Less variation / Offspring identical to the parent. In a changing environment sexual reproduction is best because the variation of the species may allow one to be successful and pass the genes on to the next generation. (1 mark) In a changing environment asexual reproduction may lead to the whole population being wiped out due to a change in selective pressures. (1 mark)

11 Multiple choice questions 1 Select the best explanation of how some bacteria are metabolically active in hot springs. (a) At high temperatures enzymes are not needed to catalyse chemical reactions. (b) Their enzymes have high optimal temperatures. (c) Their enzymes are insensitive to temperature. (d) They use molecules other than proteins to catalyse chemical reactions. An endotherm moves from a cool place to a hotter one. Which of the following changes is most likely to occur? (a) Skin muscles will contract to hold hairs erect. (b) Blood vessels near the body surface will dilate (expand). (c) Urine production will increase. (d) Body temperature will fall, to compensate

12 Multiple choice questions 1 Select the best explanation of how some bacteria are metabolically active in hot springs. (a) At high temperatures enzymes are not needed to catalyse chemical reactions. (b) Their enzymes have high optimal temperatures. (c) Their enzymes are insensitive to temperature. (d) They use molecules other than proteins to catalyse chemical reactions. An endotherm moves from a cool place to a hotter one. Which of the following changes is most likely to occur? (a) Skin muscles will contract to hold hairs erect. (b) Blood vessels near the body surface will dilate (expand). (c) Urine production will increase. (d) Body temperature will fall, to compensate

13 Multiple choice questions 2 Eastern coral snakes are brightly coloured, with red, yellow and black rings along their bodies. The snakes are poisonous and their bite kills many animals quickly. Predators rarely attack these snakes and those that do are usually killed. Which of the following is the most likely explanation of why the snakes are rarely attacked? (a) Only predators that avoid the snakes survive to breed. (b) Predators are bitten and learn to avoid the snakes. (c) The colourings camouflage the snakes. (d) The predators that survive the snake's bite pass on resistance to their offspring. A non-poisonous snake called the scarlet king snake lives in the same habitat as the eastern coral snake. The two species have similar colours. A biologist reasoned that predators would not attack scarlet king snakes because they looked so much like the dangerous eastern coral snakes. Which of the following best defines this suggestion? (a) It is an observation. (b) It is an hypothesis. (c) It is a theory. (d) It is a conclusion.

14 Multiple choice questions 2 Eastern coral snakes are brightly coloured, with red, yellow and black rings along their bodies. The snakes are poisonous and their bite kills many animals quickly. Predators rarely attack these snakes and those that do are usually killed. Which of the following is the most likely explanation of why the snakes are rarely attacked? (a) Only predators that avoid the snakes survive to breed. (b) Predators are bitten and learn to avoid the snakes. (c) The colourings camouflage the snakes. (d) The predators that survive the snake's bite pass on resistance to their offspring. A non-poisonous snake called the scarlet king snake lives in the same habitat as the eastern coral snake. The two species have similar colours. A biologist reasoned that predators would not attack scarlet king snakes because they looked so much like the dangerous eastern coral snakes. Which of the following best defines this suggestion? (a) It is an observation. (b) It is an hypothesis. (c) It is a theory. (d) It is a conclusion.

15 Multiple choice questions 3 What is the most likely environment for this plant? (a) a swampy environment (b) a tropical rainforest environment (c) an arid environment (d) a moist woodland environment

16 Multiple choice questions 3 What is the most likely environment for this plant? (a) a swampy environment (b) a tropical rainforest environment (c) an arid environment (d) a moist woodland environment

17 Extended answers a) Genetic information is stored in molecules of DNA. Using labelled diagrams describe the structure of DNA at the level of major components and describe how it carries genetic information b) From generation to generation information controlling the processes that occur in living cells is carried in DNA. Explain how the structure of DNA can carry information which can be accurately copied during cell division.

18 Extended answer a) Genetic information is stored in molecules of DNA. Using labelled diagrams describe the structure of DNA at the level of major components and describe how it carries genetic information One mark/dot point in answers below unless otherwise indicated. Maximum 10 marks/question. Diagram – showing nitrogenous base pairs - A T, C G, and sugar phosphate backbone one mark for nitrogenous pairs label on the figure, 2 marks for sugar phosphate backbone label (3 marks total) nucleotides double helix one mark for correct basic structure in the figure name bases (one mark for naming all 4) indicate pairing (each correct pairing = one mark) sequence of bases codes for amino acid structure triplet code/codons relationship to amino acids

19 Extended answer b) From generation to generation information controlling the processes that occur in living cells is carried in DNA. Explain how the structure of DNA can carry information which can be accurately copied during cell division. Diagram of DNA showing nucleotides (sugar, phosphate, nitrogen base) DNA molecule consists of chains of nucleotides parallel to each other Chains are held together by hydrogen bonds between bases There are 4 types of nucleotides due to 4 types of bases Adenosine will only bond to thymine, cytosine will only bond to guanine (base pairing rule) The information is carried within the DNA by the sequence of base pairs. Each segment of 3 nucleotides codes for one amino acid & is called a codon This information is copied to mRNA in the nucleus and carried to the ribosomes, determining which proteins are made The DNA replicates by splitting in 2, exposing the base pairs Free nucleotides within nucleus bind to the exposed bases, forming 2 exact copies Enzymes are involved in splitting the DNA and attaching new nucleotides


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