Population Genetics Lecture 1 PDF

POPULATION GENETICS AND EVOLUTION LECTURE 1 KOFI OWUSU-DAAKU –Ph.D. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 1 LECTURE I ...

POPULATION GENETICS AND EVOLUTION LECTURE 1 KOFI OWUSU-DAAKU –Ph.D. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 1 LECTURE I  KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 2 LECTURE I  MODULE ONE EVOLUTION Origin of Life KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 3 LECTURE I Four Unifying Themes of Biology 1) The Cell Theory First cells discovered by Robert Hooke in England in 1665 using 30X microscope Anton van Leeuwenhoek then used more powerful microscope (300X) to discover diversity of life in pond water German biologists Matthias Schleiden and Theodor Schwann (1839) propose cell theory KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 4 LECTURE I Four Unifying Themes of Biology 2) Molecular Basis of Inheritance Hereditary information encoded in DNA Sequences of nucleotides in DNA make up genes An organism’s complete set of genes/DNA is called a genome KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 5 LECTURE I Four Unifying Themes of Biology 3) Diversity of Life and Evolutionary Change Incredible diversity of living things on earth Eubacteria, Archaea, Eukarya domains, with Eukarya being comprised of 4 kingdoms (Protista, Plantae, Fungi and Animalia) All evolved from a common ancestral form through evolution KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 6 LECTURE I Four Unifying Themes of Biology 4) Evolutionary conservation All living things descended from simple cellular creature which existed about 2.5 billion years ago Characteristics of common ancestors are preserved in the subsequent life forms Protein classes are conserved even between kingdoms KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 7 LECTURE I  Evolution is a unifying theme in biology connects all levels of biological organization genes & environment proteins organisms population biotic physiology community development populations abiotic ecosystem evolve KOFI OWUSU-DAAKU Ph.D. population WED. FEB. 6 2019 genetics & evolution LECTURE I 8  KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 9 LECTURE I  The evolution of the environment having definite biosphere zones facilitated the evolution of higher animals including humans. The overall sequence of evolution as suggested by Oparin (1938) may be summarised in following phases: KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 10 LECTURE I  (a) Atomic phase (b) Molecular phase (c) Organic phase (d) Colloidal phase (e) Autocatalytic phase (f) Primordial cellular phase (g) Autotrophic phase (h) Prokaryotic phase (i) Eukaryotic phase KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 11 LECTURE I  ORIGIN OF LIFE The earth is also called 'the blue planet' or 'the planet with life'. It originated about 4.8 billion years ago. The primitive atmosphere of the earth contained nitrogen, hydrogen and carbon, but no oxygen or ozone, all found in the atomic state due to extreme heat and ultraviolet insulation. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 12 LECTURE I  ORIGIN OF LIFE Chemical evolution continued for about 2,000 million years, by which various inorganic and organic compounds appeared. The chief inorganic compounds that evolved during this period were N2, H2CH4. NH3. CO, CO2. H2O, etc., but no O2 or O3. as the primitive environment was reducing. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 13 LECTURE I  ORIGIN OF LIFE Miller in 1953 during his experiments on molecular evolution found that when a mixture of H2. CH4. NH3 and H2O is exposed to high electric discharge for weeks, a gaseous phase of advanced molecules including CO, CO2, N2 etc., and a liquid condensate phase, -including a variety of amino acids like glycine, valine, etc., and other organic molecules were obtained. WED. FEB. 6 2019 KOFI OWUSU-DAAKU Ph.D. population genetics & evolution 14 LECTURE I  KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 15 LECTURE I  ORIGIN OF LIFE During this period, certain compounds that favoured molecular evolution survived, while the compounds disfavouring it were destroyed by predator molecules like hydrated electrons, poly anions, etc. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 16 LECTURE I  ORIGIN OF LIFE The culmination of chemical evolution was the polymerisation of monomers. As a result, certain biopolymers like proteins, polysaccharides, lipids and polynucleotides were formed. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 17 LECTURE I  ORIGIN OF LIFE Certain polymers like histones and protamines are positively charged and called polycations and when such polycations enclosed polynucleotides, the latter were protected from the predator molecules. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 18 LECTURE I  ORIGIN OF LIFE The earliest life originated in a primitive broth, which provided easy accessibility to the polymers essential for self-replication. The first life form had the unique property of self-replication and it became the first and foremost characteristic of life. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 19 LECTURE I  ORIGIN OF LIFE Although the sun is the ultimate source of energy, the first transformed energy was obtained from the mobility of the molecules. The second primitive characteristic of tiny life was to use the ATP, the condensed energy source for all life activities. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 20 LECTURE I  ORIGIN OF LIFE The two other prerequisites of life were a definite catalytic system and an information transfer system, also formed by the conversion of the two polymers. Certain theories and principles regarding origin of life are given in the following table: KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 21 LECTURE I  ORIGIN OF LIFE The first life form produced food from inorganic substances by the photoreduction reaction in which sulphur or other organic groups were produced as byproducts. CO2 + 2H2X ----> (CH2O) + H2O + 2X KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 22 LECTURE I  ORIGIN OF LIFE The above hypothesis has been confirmed by the tracer carbon technique and chromatographic identification of the products (Arnon, 1960). KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 23 LECTURE I ORIGIN OF LIFE The evolution of chlorophyll molecule was a landmark in the origin of photosynthetic life because the magnesium porphyrin of chlorophyll molecule is capable of emitting electrons, when excited by the radiant energy of even visible range. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 24 LECTURE I  ORIGIN OF LIFE The evolution of photosynthetic life could change the reducing environment to oxidising due to release of oxygen. 6C02 + 6H2O ----> C6H1202 + 6C02 KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 25 LECTURE I  ORIGIN OF LIFE At the time of origin of animals, the atmosphere contained N2, CO2 and O2 gases, while the land mass contained soil rich in soluble nitrates, sulphates, phosphates and organic materials. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 26 LECTURE I  LAMARCKISM Jean Baptiste de Lamarck (1744- 1829) was a French scientist who for the first time put forth an evolutionary theory. He published his ideas in the book, Philosophie Zoologique in 1809. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 27 LECTURE I  LAMARCKISM Lamarckian theory is also known as 'Theory of Inheritance of Acquired Characters' or the 'Theory of Use or Disuse of Organs'. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 28 LECTURE I ACCORDING TO LAMARCK’S THEORY, AS GIRAFFES STRETCHED TO REACH THE HIGH BRANCHES THEIR NECKS LENGTHENED AND THIS WAS PASSED ON TO THEIR OFFSPRINGS KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 29 LECTURE I  LAMARCKISM The basic ideas of Lamarckism are as follows: (a) Complex plants and animals are produced from the simpler ones in due course of time under the influence of nature. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 30 LECTURE I  LAMARCKISM (b)Living organisms have a tendency to continuously increase in size. (c) There is a change in the needs of an animal due to changes in the surrounding environment. As a result, new organ(s) is/are formed to cater the needs of the animal. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 31 LECTURE I  LAMARCKISM (d) If an organ is used continuously, it will be more powerful. If it is not used for a long time, it gradually weakens and finally disappears. (e) The characters acquired during the lifetime of individuals will be transmitted to the next generation. This is called the 'inheritance of acquired characters'. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 32 LECTURE I  KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 33 LECTURE I  Critical Analysis Lamarck based his idea of use and disuse on the evidences in the form of vestigial organs and rudimentary organs. The idea is true, but it cannot be treated as a basis of evolution. As far as the theory of inheritance of acquired characters is concerned, it cannot be accepted. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 34 LECTURE I  Critical Analysis Weismann (1890) for the first time provided experimental proof against this assumption. Weismann cut off the tails of mice for many generations and kept them in breeding, but not a single mouse was born without a tail. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 35 LECTURE I  Weismann proposed the 'Theory of Continuity of Germplasm'. It is now quite clear that only those changes are inherited which are in the germ cells. No somatic changes can be inherited. Whatever one acquires in one's lifetime passes away with the end of one's life. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 36 LECTURE I  Neo Lamarckism A few scientists notably, Herbert Spencer, Haeckel, Gadow, etc., have supported Lamarckism in a modified form and this is called Neo Lamarckism. Neo Lamarckism can be explained as listed below. a) Only those acquired characters are inheritable, which are incorporated in the genetic makeup. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 37 LECTURE I  Neo Lamarckism cont`d B) Environmental changes create needs in an organism. Such needs rarely cause changes in the genetic makeup. Somatic changes are not heritable. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 38 LECTURE I  Neo Lamarckism cont`d (c) It may be that environmental changes and thereby the needs emanating from them may not reach up to a mutational threshold and genetic effect will not be expressed. The inheritance of acquired characters depends upon its reaching the mutational threshold. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 39 LECTURE I  CHARLES DARWIN INKOFI1840 WED. FEB. 6 2019 OWUSU-DAAKU Ph.D. population genetics & evolution LECTURE I 40  KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 41 LECTURE I  Darwin Influenced by Others Malthus “Essay of the Principle of Population” (1798) Populations of plants/animals can increase geometrically Populations of plants/animals remain relatively constant Death limits populations Darwin hypothesized natural selection as a means by which selective survival of individuals with superior attributes gradually changes the average characters of the population as a whole over many generations WED. FEB. 6 2019 KOFI OWUSU-DAAKU Ph.D. population genetics & evolution LECTURE I 42  Additional Evidence Supporting Darwin/Wallace Theory Molecular biology DNA Genetic code, gene expression Development An organism’s development (ontogeny) provides insights into its evolutionary history (phylogeny) Human embryos with gills, tails and fur KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 43 LECTURE I  In the 18th and 19th centuries, scientist began to overturn many commonly held beliefs in the Western world, including that the earth was only about 6,000 years old and that all species had been created separately and were unchanging. These gradual changes in scientist’ belief helped shape Charles Darwin’s thinking. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 44 LECTURE I  DARWINISM Charles Darwin (1809-1882) was the first individual who categorically explained organic evolution in detail. Charles Darwin joined a sea voyage that continued for five years in a ship named HMS Beagle and collected flora and fauna of many continents and islands. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 45 LECTURE I  KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 LECTURE I 46  H. M. S. BEAGLE IN WHICH CHARLES DARWIN SET SAIL FROM ENGLAND TO EXPLORE THE KOFI OWUSU-DAAKU Ph.D. population genetics & evolution RICH WED. FEB.FOSSIL 6 2019 BEDS OF SOUTH AMERICA LECTURE I 47  Darwin noted unexpected patterns among fossils he discovered and living organisms he observed while on the voyage of the Beagle. Fossils resembled but were not identical to the living organisms in the same area where they were found. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 48 LECTURE I  And finch species on each of the Galapagos Islands differed from each other in the small but significant ways. These observations helped Darwin develop his theory of how species might change over time. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 49 LECTURE I THICK LINES SHOW THE BEAGLES VOYAGE KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 50 LECTURE I DISTINGUISHING FEATURE OF GALAPAGOS TORTOISE IS THE SHAPE OF THE SHELL WHICH VARIES ACCORDING TO IT’S ISLAND KOFI OF OWUSU-DAAKU ORIGIN Ph.D. population genetics & evolution WED. FEB. 6 2019 51 LECTURE I A.THE RHEA OF SOUTH AMERICA KOFI WED. FEB. 6 2019 B. OWUSU-DAAKU THE EMU OF Ph.D. AUSTRALIA population C. AFRICAN OSTRICHES genetics & evolution 52 LECTURE I ALFRED RUSSEL WALLACE(1823 - 1913) KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 53 LECTURE I  After putting off publishing his thoughts on natural selection for more than 15 years, Darwin did so only after Alfred Wallace independently came up with the same idea. The two men published a joint presentation on the their ideas in 1858, and Darwin published a much more detailed treatment in the Origin of the Species in 1859, sparking wide debate and discussion of natural selection. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 54 LECTURE I  The view of A R Wallace regarding organic evolution was much similar to that of Darwin. The ideas of both scientists were greatly influenced by the writings of T R Malthus on the growth of population. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 55 LECTURE I  KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 56 LECTURE I  DARWINISM CONT`D Darwin published his detailed theory on organic evolution in 1859 in his book entitled Origin of Species He argued that natural selection is the main cause of origin of new species. The presentation of Darwin's theory was based on the following facts: KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 57 LECTURE I  DARWINISM CONT`D (a) Overproduction - Organisms have the capacity of enormous reproduction, i.e., they produce much more than required. (b) Limited Environmental Resources - The population of each species tends to increase in a geometric ratio but remains almost constant. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 58 LECTURE I  DARWINISM CONT`D (c) Struggle for Existence - To check the increase in the number of each species, there is a struggle for existence, which may be intraspecific, interspecific and environmental. Of these, the intraspecific struggle is very severe. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 59 LECTURE I  DARWINISM CONT`D (d) Variations - Darwin thought that each member of a sexually reproducing species is different from the others. The cause of difference among the members of a species is variation and the variations are heritable. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 60 LECTURE I  DARWINISM CONT`D (e) Survival of the Fittest (Natural Selection) - Among these variations, some are useful and some are harmful. Useful variations make some individuals more suited to the environment than others in the struggle for existence. In this struggle, the most suitable individuals survive. Thus, the paradigm of 'survival of the fittest' is in operation. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 61 LECTURE I  The survival of the fittest is made possible due to useful or beneficial variations, which is why the survival of the fittest is by natural selection. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 62 LECTURE I  Fitness is a measure of the relative amount of reproduction by an individual with a particular phenotype, compared with the reproductive output of individuals with alternative phenotypes. An individual’s fitness can vary, depending on the environment in the which it lives. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 63 LECTURE I  Criticism of Darwinism Darwin could not explain the origin and cause of inheritance of variations. Further, he could not differentiate heritable and non heritable variations. Although Darwin termed as 'sports' the sudden change in the genetic material, he was unable to explain it. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 64 LECTURE I  Criticism of Darwinism There are examples of overgrowth/over specialisation of useful organs that become instrumental in the extinction of that species. Darwin did not explain the occurrence of vestigial organs. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 65 LECTURE I  Neo Darwinism Neo Darwinism is the modification of Darwin's theory in the light of modern genetic findings. Neo Darwinism is based on three facts, viz., genotypic variations, natural selection and isolation. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 66 LECTURE I  Neo Darwinism cont`d Neo Darwinism assumes that natural selection acts on the heritable variations in individuals in populations and mutations provide the main source of these genetic variations. Neo Darwinism separates the Darwinian idea of natural selection from his hypothesis of pangenesis. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 67 LECTURE I  Neo Darwinism cont`d Neo Darwinism states that organic evolution takes place by natural selection of inherited characters. According to Neo Darwinism, evolution occurs because the environment is slowly changing. This exerts a selection pressure on individuals within a population. KOFI OWUSU-DAAKU Ph.D. population genetics & evolution WED. FEB. 6 2019 68 LECTURE I  Neo Darwinism cont`d The characteristics that adapt to a new environment are able to survive and pass on to the next generation. These result in variations and accumulate in the gene pool of the organisms. With the passage of time, the genetic makeup of the population changes and ultimately a new species is formed. WED. FEB. 6 2019 KOFI OWUSU-DAAKU Ph.D. population genetics & evolution LECTURE I 69