10 3 Gene pools and speciation Essential idea

10. 3 Gene pools and speciation Essential idea: Gene pools change over time. Heliconius pachinus Heliconius cydno 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

10. 3. U 1 A gene pool consists of all the genes and their different alleles, present in an interbreeding population. allele frequency Allele frequency is the proportion of all copies of a gene that is made up of a particular gene variant (allele). Example Say if a recessive allele h made up 2% of the total in a human population… gene pool The total collection of different alleles in an interbreeding 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) http: //www. flickr. com/photos/limowreck 666/171979083/

10. 3. U 2 Evolution requires that allele frequencies change with time in populations. 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. A 1 Identifying examples of directional, stabilizing and disruptive selection. 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 Phenotype (fur colour) the population will evolve, but how it evolves depends Stabilizing selection on which phenotypes are experience the greatest pressure. Key Evolved population Original population Selective pressure Phenotype (fur colour) Frequency of individuals Original population Directional selection Phenotype (fur colour) Disruptive selection Frequency of individuals Directional, stabilizing & disruptive selection Phenotype (fur colour) Rabbit image: http: //cliparts. co

10. 3. A 1 Identifying examples of directional, stabilizing and disruptive selection. Directional selection Key Frequency of individuals Evolved population Original population Selective pressure Phenotype (fur colour) Medium ground finch Beak shape and size in Geospiza fortis Selective pressure: during dry years small seeds are not abundant. Result: Birds with larger tougher beaks become more frequent Example from 5. 2. A 1 Changes in beaks of finches on Daphne Major.

10. 3. A 1 Identifying examples of directional, stabilizing and disruptive selection. Frequency of individuals Stabilizing selection Key Evolved population Original population Selective pressure Phenotype (fur colour) Human birth weight 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. Mayumi Paine (aged 1 day) – photo by Chris Paine

10. 3. A 1 Identifying examples of directional, stabilizing and disruptive selection. Frequency of individuals Disruptive selection 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: 20150628 Anthoxanthum_odoratum 3. jpg

10. 3. U 3 Reproductive isolation of populations can be temporal, behavioural or geographic. The circumstances preventing different species from interbreeding are known as reproductive isolating mechanisms https: //youtu. be/rlf. Nvoyijmo The 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. 3. U 3 Reproductive isolation of populations can be temporal, behavioural or geographic. The reproductive isolation only promotes selection in sexually reproducing organisms: it doesn’t apply to singlecelled organisms. Rats! http: //www. flickr. com/photos/microagua/3721497804/

10. 3. U 3 Reproductive isolation of populations can be temporal, behavioural or geographic. Temporal isolation Pinus radiata (Monterey Pine) Pinus attenuata (Knobcone pine) Pollen Production MAX J F M A M J J Month A S O N D 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. *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 http: //www. flickr. com/photos/alancleaver/4293345631/

10. 3. U 3 Reproductive isolation of populations can be temporal, behavioural or geographic. Ecological isolation The two species are in the same area, but live in different habitats I love me some Ca. CO 3 in my soil Blechhh! Acidic soils are more my thing Viola arvensis http: //www. flickr. com/photos/annetanne/3035068940/ Viola tricolor http: //www. flickr. com/photos/carinemily/644052381/

10. 3. U 3 Reproductive isolation of populations can be temporal, behavioural or geographic. 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. http: //www. pbs. org/wgbh/evolution/library/05/2/swf_pop/l_052_01. html Yo! I don’t like your music! Its like, totally mutual! http: //www. flickr. com/photos/nrk-p 3/2333221093/ http: //www. flickr. com/photos/rowelbg/2895578034/

10. 3. S 1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies Pan. I is a gene in cod fish that codes for an integral membrane protein called pantophysin. Two alleles of the gene, Pan. IA and Pan. IB, 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 alleles always being 1. 0. 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 (Pan. I) allele frequencies in NE Atlantic cod Gadus morhua. ” MEPS. Vol 301. Pp 267– 278. Figs 1 and 3. Key Pan. IA Population # 12 Pan. IB

10. 3. S 1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies 1. State the two populations with the highest Pan. IB allele frequencies. [1] 2. State the population in which the allele frequencies were closest to 0. 5. [1] 3. Deduce the allele frequencies of a population in which half of the cod fish had the genotype Pan. IA, and half had the genotype Pan. IA Pan. IB. [2] Key Pan. IA Population # Graph and questions from IB Questionbank 12 Pan. IB

10. 3. S 1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies 1. State the two populations with the highest Pan. IB allele frequencies. [1] 1 and 2 2. State the population in which the allele frequencies were closest to 0. 5. [1] 7/11 3. Deduce the allele frequencies of a population in which half of the cod fish had the genotype Pan. IA, and half had the genotype Pan. IA Pan. IB. [2] Pan. IA 0. 75 and Pan. IB 0. 25 Key Pan. IA Population # Graph and questions from IB Questionbank 12 Pan. IB

10. 3. S 1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies 4. Identify an example of two geographically isolated populations. [1] 5. Give Suggestions why the Pan. IB allele is more common in population 13 than population 22. [2] Key Pan. IA Population # Graph and questions from IB Questionbank 12 Pan. IB

10. 3. S 1 Comparison of allele frequencies of geographically isolated populations. Comparison of allele frequencies 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 Pan. IB allele is more common in population 13 than population 22. [2] Cooler water temperature favours Pan. IB; Interbreeding with icelandic/more northern populations; Key Pan. IA Population # Graph and questions from IB Questionbank 12 Pan. IB

10. 3. U 4 Speciation due to divergence of isolated populations can be gradual. AND 10. 3. U 5 Speciation can occur abruptly. The rate of speciation varies 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. http: //www. ib. bioninja. com. au/_Media/pace_of_evolution_med. jpeg

10. 3. U 4 Speciation due to divergence of isolated populations can be gradual. 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. U 5 Speciation can occur abruptly. 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 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/ideonexus/4022727065/ http: //www. flickr. com/photos/mrccos/288136783/sizes/m/in/photostream/

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) 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 divide up http: //commons. wikimedia. org/wiki/File: Haploid, _diploid_, triploid_and_tetraploid. svg Edited from: http: //www. slideshare. net/jasondenys/ib-biology-option-d 2 -species-and-speciation

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) 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 results in Down 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 (2 n) daughter cells from meiosis instead of the usual four (n) daughter cells. 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

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) Polyploidy in animals and plants However, polyploidy is a great source of speciation amongst plants. There exist few polyploid animals species (examples include salamanders, goldfish and salmon). Polyploidy often leads to increased size, resistance to disease and overall vigour. Many agricultural plants are polyploid (e. g. wheat) due to having bigger fruits, seeds and storage organs https: //youtu. be/6 Jjilc 5 eq. S 0 https: //commons. wikimedia. org/wiki/File: Wheat_close-up. JPG Edited from: http: //www. slideshare. net/jasondenys/ib-biology-option-d 2 -species-and-speciation

10. 3. A 2 Speciation in the genus Allium by polyploidy. Chromosome number in genus Allium Many species of this genus commonly reproduce asexually and if polyploidy confers an advantage a new species may arise. English Leek (A. Cepa), 32 Chromosomes Onion (A. Cepa), 16 Chromsomes https: //commons. wikimedia. org/wiki/File: Poireaux_artlibre_jnl. jpg https: //commons. wikimedia. org/wiki/File: Starr_0703135652_Allium_cepa. jpg