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10.3 gene pools and speciation

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IB Biology 2015

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10.3 gene pools and speciation

  1. 1. 10.3 Gene Pools and Speciation Essential idea: Gene pools change over time.
  2. 2. Understandings Statement Guidance 10.3 U.1 A gene pool consists of all the genes and their different alleles, present in an interbreeding population. 10.3 U.2 Evolution requires that allele frequencies change with time in populations. Punctuated equilibrium implies long periods without appreciable change and short periods of rapid evolution. 10.3 U.3 Reproductive isolation of populations can be temporal, behavioral or geographic. 10.3 U.4 Speciation due to divergence of isolated populations can be gradual. 10.3 U.5 Speciation can occur abruptly.
  3. 3. Applications and Skills Statement Utilization 10.3 A.1 Identifying examples of directional, stabilizing and disruptive selection. 10.3 A.2 Speciation in the genus Alliumby polyploidy. Many crop species have been created to be polyploid. Polyploidy increases allelic diversity and permits novel phenotypes to be generated. It also leads to hybrid vigor. 10.3 S.1 Comparison of allele frequencies of geographically isolated populations.
  4. 4. 10.3 U.1 A gene pool consists of all the genes and their different alleles, present in an interbreeding population Speciation • A species a group of individuals who produce offspring after mating. This make individual of that species reproductively isolated from other species. • A gene pool is the set of all genes, in an interbreeding population. http://data1.whicdn.com/images/63849/large.jpghttp://arkansasagnews.uark.edu/monarchs95.jpg
  5. 5. 10.3 U.2 Evolution requires that allele frequencies change with time in populations. If the allele frequencies of a population are not in equilibrium then the frequencies are changing or evolving. The following processes facilitate evolution by either adding or removing genetic variation from a population: • Mutation • Migration (Gene Flow) • Genetic Drift • Unequal Mating and/or Fertilization Success (Sexual Selection) • Unequal Viability (Natural Selection) Gene pool: The collection of genes in a population Because diploids have only two versions of each gene, each has only a small fraction of possible alleles in a population Genotype: The genetic makeup of an individual at a given locus, taking into account the two possible alleles Genotype frequency is the proportion of a given genotype in the population Allele frequency refers to the proportion of a particular allele, such as A or a Phenotype: the traits of an individual Phenotype frequency is the proportion of a given phenotype in the population Phenotype frequency is influenced by the dominance characteristic of an allele
  6. 6. 10.3 U.2 Evolution requires that allele frequencies change with time in populations.
  7. 7. Frequencies add up to 1.0 e.g. — a population has two alleles, A and a with A is dominant over a The allele frequencies must sum to 1.0 (frequency of A) + (frequency of a) = 1.0 The genotype frequencies must sum to 1.0 (frequency of AA) + (frequency of Aa) + (frequency of aa) = 1.0 The phenotype frequencies must sum to 1.0 (frequency of AA and Aa phenotype) + (frequency of aa phenotype) = 1.0 Imagine 2 alleles, A and a p is the frequency of A q the frequency of a So, p + q = 1 The mathematical equivalent of a random mating can be given by multiplying this relationship by itself Therefore, (p + q)2 = 1 = p2 + 2pq + q2 p2 = frequency of AA 2pq = frequency of Aa q2 = frequency of aa Given this condition, we can always work out the frequencies of each allele in a sexual population. 10.3 U.2 Evolution requires that allele frequencies change with time in populations.
  8. 8. 10.3 U.2 Evolution requires that allele frequencies change with time in populations. • Evolution is the cumulative change in allele frequency or heritable characteristics in a population over time • The cumulative change can occur as a result of genetic changes and/or selective pressures which favor certain heritable characteristics over other less favorable characteristics • These populations have to be reproductively isolated, thus preventing gene flow between populations P equals the dominant gene Q equals the recessive gene
  9. 9. 10.3 S.1 Comparison of allele frequencies of geographically isolated populations • Cod fish have a gene that codes for an integral membrane protein called pantophysin. • Two alleles of the gene, PanIA and PanIB, code for versions of pantophysin, that differ by four amino acids in one region of the protein. • Samples were collected from 23 locations in the North Atlantic (numbered 1–23 in each pie chart), on the map to the right. • The frequency of an allele can vary from 0.0 to 1.0. PanIA light grey sectors of the pie charts show the allele frequency for the PanIA gene PanIB black sectors show the allele frequency for the PanIB gene. • The biggest difference in allele frequency occurs in the Cod fish isolated at the two extremes of the map.
  10. 10. 10.3 U.3 Reproductive isolation of populations can be temporal, behavioral or geographic. • Reproductive isolation of populations occurs when barriers or mechanisms prevent two populations from interbreeding, keeping their gene pools isolated from each other. • There are different types of reproductive isolation including temporal, behavioral, and geographic
  11. 11. How and why do new species originate? • Species are created by a series of evolutionary processes – populations become isolated • geographically isolated • reproductively isolated – isolated populations evolve independently • Isolation – allopatric • geographic separation – sympatric • still live in same area 10.3 U.3 Reproductive isolation of populations can be temporal, behavioral or geographic.
  12. 12. 10.3 U.3 Reproductive isolation of populations can be temporal, behavioral or geographic. Temporal isolation • Species that breed during different times of day, different seasons, or different years cannot mix gametes – reproductive isolation – sympatric speciation • “same country” Eastern Spotted Skunk (Top Right) & Western Spotted Skunk (Bottom Right) overlap in range but Eastern mates in late winter & Western mates in late summer http://upload.wikimedia.org/wikipedia/ commons/f/f2/Spilogale_putorius_(2).jp g http://upload.wikimedia.org/wikipe dia/commons/9/98/Spilogale_gracil is_amphiala.jpg
  13. 13. 10.3 U.3 Reproductive isolation of populations can be temporal, behavioral or geographic. Behavioral Isolation • In most animal species, members of the two sexes must first search for each other and come together. • Unique behavioral patterns & rituals isolate species  identifies members of species attract mates of same species  courtship rituals, mating calls  reproductive isolation Blue footed boobies mate only after a courtship display unique to their specieshttp://upload.wikimedia.org/wikipedia/commo ns/a/aa/Bluefooted_Booby_Comparison.jpg
  14. 14. So…what is a species? Western MeadowlarkEastern Meadowlark Distinct species: songs & behaviors are different enough to prevent interbreeding 10.3 U.3 Reproductive isolation of populations can be temporal, behavioral or geographic.
  15. 15. 10.3 U.3 Reproductive isolation of populations can be temporal, behavioral or geographic. Geographic Isolation Species occur in different areas – physical barrier – allopatric speciation • “other country” Harris’s Antelope Squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related White-tailed Antelope Squirrel
  16. 16. 10.3 A.1 Identifying examples of directional, stabilizing and disruptive selection. • If no selection occurs to a population (for whatever means), population doesn’t change with succeeding generations. • If selection pressure is applied then those not receiving selection pressure tend to predominate…  Stabilizing: the extremes are selected against; center stays same and grows in numbers  Directional: one tail of the distribution is selected against and the opposite tail grows in numbers  Disruptive: a mid-group is selected against; the tails are allowed to predominate and grow compared to middle As an example: in Humans we have selected for a babies birth weight. This protects the mother and the babies health.
  17. 17. 10.3 A.1 Identifying examples of directional, stabilizing and disruptive selection. Directional Selection: • Selection that removes individuals from one end of a phenotypic distribution and thus causes a shift in the distribution towards the other end. • Over time, the favored extreme will become more common and the other extreme will be less common or lost.
  18. 18. 10.3 A.1 Identifying examples of directional, stabilizing and disruptive selection. Stabilizing Selection: A type of selection that removes individuals from both ends of a phenotypic distribution, thus maintaining the same distribution mean. This occurs when natural selection favors the intermediate phenotypes. Over time, the intermediate states become more common and each extreme variation will become less common or lost. Same mouse example where medium colored fur is favored over dark or light fur color.
  19. 19. 10.3 A.1 Identifying examples of directional, stabilizing and disruptive selection. Disruptive Selection: • Removes individuals from the center of a phenotype. This occurs when natural selection favors both ends of the phenotypic variation. • Over time, the two extreme variations will become more common and the intermediate states will be less common or lost. • This can lead to two new species.
  20. 20. 10.4 U.4 Speciation due to divergence of isolated populations can be gradual. • Speciation can occur gradually over long periods of time, with several intermediate forms in between species leading to today’s current species. This can be seen in some of the more complete fossil records, like the whale or the horse. • In some species, large gaps were evident for certain species in the fossil record. This imperfections in the fossil record, maybe the result of transitional species have not been discovered yet or abrupt speciation. http://www.sivatherium.narod.ru/library/Dixon/pics_01/p0010_e.gif
  21. 21. Gradualism • Gradual divergence over long spans of time – assume that big changes occur as the accumulation of many small ones 10.4 U.4 Speciation due to divergence of isolated populations can be gradual. http://cnx.org/resources/22b17901c8ce6510b03e2f89df0bc072/graphics1.png
  22. 22. 10.3 U.5 Speciation can occur abruptly. Punctuated Equilibrium Species remain stable for long periods of time (several million years) interrupted by periods of significant change, during which time a new species may evolve.  rapid bursts of change  long periods of little or no change  species undergo rapid change when they 1st bud from parent population
  23. 23. 10.3 U.5 Speciation can occur abruptly. http://static.skynetblogs.be/media/130852/12.11.jpg Over 75% of all life on Earth was lost during the late Devonian mass extinction which took place about 375-359 million years ago
  24. 24. 10.3 U.5 Speciation can occur abruptly. https://evolutionliteracy.files.wordpress.com/2014/09/t rilobites-evolution-literacy-g-paz-y-mino-c-photo.jpg Over 97% of all life on Earth was lost during the End-Permian mass extinction which took place 252 million years ago
  25. 25. 10.3 U.5 Speciation can occur abruptly. http://www.gohobby.com/wp- content/uploads/2012/11/Velociraptor- Jurassic-Park.jpeg Over 50% of all life on Earth was lost during the Triassic mass extinction which took place 201 million years ago
  26. 26. 10.3 U.5 Speciation can occur abruptly. https://evolutionliteracy.files.wordpress.com/2014/09/t rilobites-evolution-literacy-g-paz-y-mino-c-photo.jpg Over 80% of all life on Earth was lost during the end Cretaceous. The mass extinction took place 65 million years ago
  27. 27. Gradualism Punctuated Equilibrium 10.3 U.5 Speciation can occur abruptly.
  28. 28. 10.3 A.2 Speciation in the genus Alliumby polyploidy. • Polyploidy organisms contain more than two pairs of the same chromosomes. • A likely advantage is it allows for additional raw materials (i.e. DNA, genes) for evolution. Every gene is theoretically free to evolve without substantial negative effect. • Polyploidy plants tend to be larger. The reproductive organs and fruit, in particular, are usually enlarged in polyploidy. The likely mechanism for this is simple: more DNA results in a larger nucleus, which results in larger cells, especially in the reproductive organs. http://www.vims.edu/newsandevents/top stories/_images/diploid_triploid_250.jpg Oysters
  29. 29. 10.3 A.2 Speciation in the genus Alliumby polyploidy.
  30. 30. 10.3 A.2 Speciation in the genus Alliumby polyploidy. • The genus Allium comprises monocot flowering plants and includes the onion, garlic, chives, scallion, shallot, and the leek. • In many of these species of plants, chromosome doubling has created a large number of different phenotypes. • This results is a number of reproductively isolated but similar populations. Examples: of this are seen in 7 natural populations Allium grayi. They showed • tetraploid (2n=32) • pentaploid (2n=40) • hexaploid (2n=48) http://i.dailymail.co.uk/i/pix/2008/09/12/article-1054890- 029CF17900000578-854_233x364.jpg
  31. 31. 10.3 A.2 Speciation in the genus Alliumby polyploidy. Allium grayi tetraploid (2n=32) tetraploid (2n=32)
  32. 32. 10.3 A.2 Speciation in the genus Alliumby polyploidy. pentaploid (2n=40)
  33. 33. 10.3 A.2 Speciation in the genus Alliumby polyploidy. http://upload.wikimedia.org/wikipedia/commons/7/79/Allium_tulipifolium_(inflorescence).jpg hexaploid (2n=48)

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