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BioKnowledgy Presentation on 10.3 Gene pools and speciation (AHL)

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BioKnowledgy Presentation on 10.3 Gene pools and speciation (AHL)

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BioKnowledgy Presentation on 10.3 Gene pools and speciation (AHL)

  1. 1. 10.3 Gene pools and speciation (AHL) Essential idea: Gene pools change over time. The two butterfly species of the Heliconius genus above have only recently diverged and consequently differ in twelve regions of their genomes. Other species of the genus diverged earlier show hundreds of genomic changes. http://phys.org/news/2013-10-evolution-species-requires-genetic.html By Chris Paine https://bioknowledgy.weebly.com/ Heliconius pachinus Heliconius cydno photos from http://www.heliconius.net
  2. 2. Understandings, Applications and Skills Statement Guidance 10.3.U1 A gene pool consists of all the genes and their different alleles, present in an interbreeding population. 10.3.U2 Evolution requires that allele frequencies change with time in populations. 10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic. 10.3.U4 Speciation due to divergence of isolated populations can be gradual. 10.3.U5 Speciation can occur abruptly. Punctuated equilibrium implies long periods without appreciable change and short periods of rapid evolution. 10.3.A1 Identifying examples of directional, stabilizing and disruptive selection. 10.3.A2 Speciation in the genus Allium by polyploidy. 10.3.S1 Comparison of allele frequencies of geographically isolated populations.
  3. 3. http://www.flickr.com/photos/limowreck666/171979083/ allele frequency Allele frequency is the proportion of all copies of a gene that is made up of a particular gene variant (allele). gene pool The total collection of different alleles in an interbreeding population. Example Say if a recessive allele h made up 2% of the total in a human population… …then the dominant allele H would make up 98%. The frequency for h would be expressed as 0.02 and for H 0.98 Recessive allele frequency + dominant allele frequency = 1 (for characteristics determined by two alleles) 10.3.U1 A gene pool consists of all the genes and their different alleles, present in an interbreeding population.
  4. 4. New combinations of alleles lead to new phenotypes that can then be selected for or against by the environment. This leads to evolutionary change in the species 10.3.U2 Evolution requires that allele frequencies change with time in populations.
  5. 5. 10.3.A1 Identifying examples of directional, stabilizing and disruptive selection. Frequencyofindividuals Phenotype (fur colour) Frequencyofindividuals Phenotype (fur colour) Frequencyofindividuals Phenotype (fur colour) Frequencyofindividuals Phenotype (fur colour) Directional, stabilizing & disruptive selection Disruptive selection Directional selection Stabilizing selection Rabbit image: http://cliparts.co Key Evolved population Original population Selective pressure Original population If the selective pressures applied to a population do not change then the population will not evolve. However if the selective pressures do change then the population will evolve, but how it evolves depends on which phenotypes are experience the greatest pressure.
  6. 6. Medium ground finch Beak shape and size in Geospiza fortis http://commons.wikimedia.org/wiki/File:Geospiza_fortis.jpg 10.3.A1 Identifying examples of directional, stabilizing and disruptive selection. Frequencyofindividuals Phenotype (fur colour) Directional selection Key Evolved population Original population Selective pressure Selective pressure: during dry years small seeds are not adundant. Result: Birds with larger tougher beaks become more frequent Example from 5.2.A1 Changes in beaks of finches on Daphne Major.
  7. 7. 10.3.A1 Identifying examples of directional, stabilizing and disruptive selection. Stabilizing selection Frequencyofindividuals Phenotype (fur colour) Key Evolved population Original population Selective pressure Selective pressures: Babies of low weight lose heat more quickly and get ill from infectious diseases more easily. Babies of large body weight are more difficult to deliver through the pelvis. Result: Medium weight babies have a much lower mortality and hence the frequency of medium weight babies increases. Human birth weight Mayumi Paine (aged 1 day) – photo by Chris Paine
  8. 8. 10.3.A1 Identifying examples of directional, stabilizing and disruptive selection. Disruptive selection Frequencyofindividuals Phenotype (fur colour) Key Evolved population Original population Selective pressure Grass (Anthoxanthum odoratum) Selective pressure: soil close to mine workings contaminated with metals, e.g. copper. Result: Two distinct grass populations arise; slower growing metal- tolerant and faster growing non-tolerant populations. https://commons.wikimedia.org/wiki/File:20150628Anthoxanthum_odoratum3.jpg
  9. 9. The circumstances preventing different species from interbreeding are known as reproductive isolating mechanisms 10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic. https://youtu.be/rlfNvoyijmo Your syllabus focuses on three ways in which populations can be isolated to prevent reproduction: • Temporal – timing • Behavourial (this affects only animals) • Geographic *This video also looks at other aspects of the topic including polyploidy, but remember it is not an IB course specific resource so make sure that you know what is relevant to you.
  10. 10. The reproductive isolation only promotes selection in sexually reproducing organisms: it doesn’t apply to single- celled organisms. Rats! http://www.flickr.com/photos/microagua/3721497804/ 10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic.
  11. 11. Temporal isolation J F M A M J J A S O N D MAX Pinus radiata (Monterey Pine) Pinus attenuata (Knobcone pine) PollenProduction Pinus radiata and Pinus attenuata are prevented from hybridising because they have separate pollination times. They can be made to hybridise by pollinating them manually. http://www.flickr.com/photos/alancleaver/4293345631/ *Random fact: The Monterey pine is at risk in it’s native range but is one of the most common plantation trees in the world. If you see a pine forest in Australia or NZ, it is probably Pinus radiata Month 10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic.
  12. 12. Ecological isolation The two species are in the same area, but live in different habitats http://www.flickr.com/photos/annetanne/3035068940/ http://www.flickr.com/photos/carinemily/644052381/ I love me some CaCO3 in my soil Blechhh! Acidic soils are more my thing Viola arvensis Viola tricolor 10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic.
  13. 13. Behavioural isolation Animals exhibit courting behaviour (song, dance etc.) or release pheremones to attract mates. Individuals are only attracted to, and will only mate with, members of the opposite sex who perform the appropriate ritual or release the correct chemical. Yo! I don’t like your music! Its like, totally mutual! http://www.flickr.com/photos/rowelbg/2895578034/http://www.flickr.com/photos/nrk-p3/2333221093/ 10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic. http://www.pbs.org/wgbh/evolution/library/05/2/swf_pop/l_052_01. html
  14. 14. 10.3.S1 Comparison of allele frequencies of geographically isolated populations. PanI is a gene in cod fish that codes for an integral membrane protein called pantophysin. Two alleles of the gene, PanIA and PanIB, code for versions of pantophysin. Samples of cod fish were collected from 23 populations in the north Atlantic and tested to find the proportions of the alleles in each population. The proportions of alleles in a population are called the allele frequencies. The frequency can vary from 0.0 to 1.0 with the total frequency of all alleles always being 1.0. Comparison of allele frequencies Key 12 PanIA PanIB Population # Use the information and charts to answer the questions on the following slides… Source: RAJ Case et al. 2005. “Macro- and micro-geographic variation in pantophysin (PanI) allele frequencies in NE Atlantic cod Gadus morhua.” MEPS. Vol 301. Pp 267–278. Figs 1 and 3.
  15. 15. 10.3.S1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies Key 12 PanIA PanIB Population # 1. State the two populations with the highest PanIB allele frequencies. [1] 1. State the population in which the allele frequencies were closest to 0.5. [1] 1. Deduce the allele frequencies of a population in which half of the cod fish had the genotype PanIA PanIA, and half had the genotype PanIA PanIB. [2] Graph and questions from IB Questionbank
  16. 16. 10.3.S1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies Key 12 PanIA PanIB Population # 1. State the two populations with the highest PanIB allele frequencies. [1] 1 and 2 1. State the population in which the allele frequencies were closest to 0.5. [1] 7/11 1. Deduce the allele frequencies of a population in which half of the cod fish had the genotype PanIA PanIA, and half had the genotype PanIA PanIB. [2] PanIA 0.75 and PanIB 0.25 Graph and questions from IB Questionbank
  17. 17. 10.3.S1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies Key 12 PanIA PanIB Population # 4. Identify an example of two geographically isolated populations. [1] 5. Give Suggestions why the PanIB allele is more common in population 13 than population 22. [2] Graph and questions from IB Questionbank
  18. 18. 10.3.S1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies Key 12 PanIA PanIB Population # 4. Identify an example of two geographically isolated populations. [1] any population from 14 – 23 and any population from 1 – 4 5. Give Suggestions why the PanIB allele is more common in population 13 than population 22. [2] Cooler water temperature favours PanIB; Interbreeding with icelandic/more northern populations; Graph and questions from IB Questionbank
  19. 19. 10.3.U4 Speciation due to divergence of isolated populations can be gradual. AND 10.3.U5 Speciation can occur abruptly. http://www.ib.bioninja.com.au/_Media/pace_of_evolution_med.jpeg Phyletic Gradualism • Evolution occurs at a constant pace over a long period of time (due to the accumulation of mutations). • For example the change in size and hoof of the modern horse. Punctuated Equilibrium • Long periods of stability are interrupted by ‘During rapid’ evolutionary changes. • periods of stability well-suited organisms have no reason to evolve until large environmental changes (e.g. meteor strikes) cause selection pressures to shift. • Gaps in the fossil record show mass extinction events. The rate of speciation varies
  20. 20. Gradualism is the older idea. Darwin is one of the originators of the concept, borrowing from his friend Charles Lyell. Darwin recognised however that not all species evolve at the same rate all of the time "I think case must be that one generation should have as many living as now. To do this and to have as many species in same genus (as is) requires extinction . Thus between A + B the immense gap of relation. C + B the finest gradation. B+D rather greater distinction. Thus genera would be formed. Bearing relation" (next page begins) "to ancient types with several extinct forms" http://commons.wikimedia.org/wiki/File:Darwin_tree.png 10.3.U4 Speciation due to divergence of isolated populations can be gradual.
  21. 21. Punctuated equilibrium was first proposed by palaeontologists Niles Eldredge and Stephen Jay Gould in 1972. They were the first to suggest that species did not change for long periods of time but were in stasis until events punctuated (disrupted) the equilibrium (balance) Richard Dawkins is a prominent critic of the theory TOK - Find out more: • What evidence are the two theories based on? • Gould (deceased) and Dawkins have both become popular writers. How does this affect the weight of their opinion: • In the scientific community? • In the wider community? http://www.flickr.com/photos/mrccos/288136783/sizes/m/in/photostream/ http://www.flickr.com/photos/ideonexus/4022727065/ 10.3.U5 Speciation can occur abruptly.
  22. 22. So far you’ve learnt that cells contain two homologous sets of chromosomes. Well….. that isn’t always the case. It goes on: Pentaploid Hexaploid Septaploid Octaploid Etc. up to: 84-ploid and 1260 chromosomes Ophioglossum reticulatum A small fern. The incredible thing is that this plant is able to carry out meiosis accurately with 1260 chromosomes to divvy up http://commons.wikimedia.org/wiki/File:Haploid,_diploid_,triploid_and_tetraploid.svg Nature of science: Looking for patterns, trends and discrepancies - patterns of chromosome number in some genera can be explained by speciation due to polyploidy. (3.1) Edited from: http://www.slideshare.net/jasondenys/ib-biology-option-d2-species-and-speciation
  23. 23. How polyploidy happens When non-disjunction occurs during meiosis in humans, an individual can end up with an extra chromosome or missing chromosomes (e.g. An extra chromosome 21 means Downs syndrome). Total non-disjunction, is when one of the two cells produced during Meiosis I gets all of the chromosomes. The other cell is not viable and is reabsorbed. This results in two (2n) daughter cells from meiosis instead of the usual four (n) daughter cells. Nature of science: Looking for patterns, trends and discrepancies—patterns of chromosome number in some genera can be explained by speciation due to polyploidy. (3.1) http://www.ib.bioninja.com.au/_Media/polyploidy_med.jpeg Polyploidy is much more common in plant species - they lack separate sexes and are capable of asexual reproduction (self-pollination) Tetraploid offspring cannot mate with diploid organisms (triploid offspring tend to be infertile), speciation has occurred Edited from: http://www.slideshare.net/jasondenys/ib-biology-option-d2-species-and-speciation
  24. 24. There exist few polyploid animals species (examples include salamanders, goldfish and salmon). Polyploidy often leads to increased size, resistance to disease and overall vigour. However, polyploidy is a great source of speciation amongst plants. https://youtu.be/6Jjilc5eqS0 Nature of science: Looking for patterns, trends and discrepancies—patterns of chromosome number in some genera can be explained by speciation due to polyploidy. (3.1) Many agricultural plants are polyploid (e.g. wheat) due to having bigger fruits, seeds and storage organs Polyploidy in animals and plants https://commons.wikimedia.org/wiki/File:Wheat_close-up.JPG Edited from: http://www.slideshare.net/jasondenys/ib-biology-option-d2-species-and-speciation
  25. 25. 10.3.A2 Speciation in the genus Allium by polyploidy. Chromosome number in genus Allium https://commons.wikimedia.org/wiki/File:Starr_070313- 5652_Allium_cepa.jpg Onion (A. Cepa), 16 Chromsomes https://commons.wikimedia.org/wiki/File:Poireaux_artlibre_jnl. jpg English Leek (A. Cepa), 32 Chromosomes Many species of this genus commonly reproduce asexually and if polyploidy confers an advantage a new species may arise.
  26. 26. Bibliography / Acknowledgments Bob Smullen Jason de Nys

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