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Perspective On The Place of Evolution in Biology Dr. Usman Qazi 18-4-11 Science and Religion Lecture. …From so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved” (Origin of Species) .
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Perspective On The Place of Evolution in BiologyDr. UsmanQazi18-4-11Science and Religion Lecture
…From so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved” (Origin of Species). “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy” (Hamlet, act 1, scene V).
Unifying Principles of Biology Fundamental organization of living organisms • Cell are the basic units of life - Immediate impact on pathology (cellular origin of disease) - Counter example: Viruses (still need cells to replicate) • New species and inherited traits are the product of evolution • Genes are the basic unit of heredity. • An organism regulates its internal environment to maintain a stable and constant condition • Living organisms consume and transform energy.
Primacy of Information: Sequence Determines Structure • DNA is the material of heredity Each strand is a linear sequence made of four nucleic acids (A, C, G, T) joined to a backbone • Strands are paired via specific attractive forces (A – T and G – C) • Either strand can be the coding strand for a gene • A gene has two portions: (a) control region and (b) coding region • Coding region makes an RNA transcript (of nucleic acids) • Levels of transcription are modulated via the control region • External signals or gene products can interact with control regions of other genes as transcription factors, and activate or inhibit them. • In eukaryotes, not all DNA is transcribed
Primacy of Information: Sequence Determines Structure • DNA is the material of heredity Each strand is a linear sequence made of four nucleic acids (A, C, G, T) joined to a backbone • Strands are paired via specific attractive forces (A – T and G – C) • Either strand can be the coding strand for a gene • A gene has two portions: (a) control region and (b) coding region • Coding region makes an RNA transcript (of nucleic acids) • Levels of transcription are modulated via the control region • External signals or gene products can interact with control regions of other genes as transcription factors, and activate or inhibit them. • In eukaryotes, not all DNA is transcribed
Primacy of Information: Sequence Determines Structure • DNA is the material of heredity Each strand is a linear sequence made of four nucleic acids (A, C, G, T) joined to a backbone • Strands are paired via specific attractive forces (A – T and G – C) • Either strand can be the coding strand for a gene • A gene has two portions: (a) control region and (b) coding region • Coding region makes an RNA transcript (of nucleic acids) • Levels of transcription are modulated via the control region • External signals or gene products can interact with control regions of other genes as transcription factors, and activate or inhibit them. • In eukaryotes, not all DNA is transcribed
RNA transcript is used to make a protein.DNA: ACGTRNA: ACGU; Genetic code: codons in RNA transcript code for all 20 amino acids
How do molecular events organize multitudes of cells into specific body parts (leaf, flower, bone)?Using switches called transcription factors
Example of gene expression during developmentBMP4 instructs cells in webbing of the developing foot to undergo programmed cell death
Challenge: Classify organismsMorphology, embryology played a fundamental roleComparison of DNA sequences has revolutionized classification Main branches of the three of life • Eukaryotes (karyon: kernel = nucleus) • Cells have internal compartments • Prokaryotes • Smaller than typical eukaryotes • Genetic material is not compartmentalized • Archaea • - Unicellular organisms that appear closer to eukaryotes based on molecular sequences
Example of a highly conserved protein: Cytochrome c • Chickens and turkeys have identical sequence homology (amino acid for amino acid) • Ducks possess molecules differing by one amino acid. • Humans and chimpanzees have the identical molecule, while rhesus monkeys share all but one of the amino acids. • Pigs, cows and sheep also share identical cytochrome c molecules.
Jean Baptiste de Lamarck (1744-1829), ZoologicalPhilosophy Individuals change due to environmental influences. These acquired changes are then passed on to offspring. Thus, the diversity of organisms is a result of organisms adapting to the environment because of individual needs. Example: Giraffe necks, blacksmith arms Theory was based on observations. Ideas of genetics and heredity came later. History of Theories Explaining Evolution Alfred Russell Wallace (1823-1913), On the Tendency of Varieties to Depart Indefinitely from the Original Type. Useful variations will tend to increase, unuseful or hurtful variations to diminish. Changes in species are not adaptations to their environment. Instead, some qualities of an individual may allow it to outlive others [Survival of the fittest]. Charles Darwin (1809-1882), On the Origin of Species. Used own observations, understanding of embryological and physical similarities among animals, their geographical distribution, geological record. Also referred to co-adaptation between two species and a study of artificial selection/selective breeding. Species do not arise independently; but are rather descendents of other species.
Jean Baptiste de Lamarck (1744-1829), ZoologicalPhilosophy Individuals change due to environmental influences. These acquired changes are then passed on to offspring. Thus, the diversity of organisms is a result of organisms adapting to the environment because of individual needs. Example: Giraffe necks, blacksmith arms Theory was based on observations. Ideas of genetics and heredity came later. History of Theories Explaining Evolution Alfred Russell Wallace (1823-1913), On the Tendency of Varieties to Depart Indefinitely from the Original Type. Useful variations will tend to increase, unuseful or hurtful variations to diminish. Changes in species are not adaptations to their environment. Instead, some qualities of an individual may allow it to outlive others [Survival of the fittest]. Charles Darwin (1809-1882), On the Origin of Species. Used own observations, understanding of embryological and physical similarities among animals, their geographical distribution, geological record. Also referred to co-adaptation between two species and a study of artificial selection/selective breeding. Species do not arise independently; but are rather descendents of other species.
Jean Baptiste de Lamarck (1744-1829), ZoologicalPhilosophy Individuals change due to environmental influences. These acquired changes are then passed on to offspring. Thus, the diversity of organisms is a result of organisms adapting to the environment because of individual needs. Example: Giraffe necks, blacksmith arms Theory was based on observations. Ideas of genetics and heredity came later. History of Theories Explaining Evolution Alfred Russell Wallace (1823-1913), On the Tendency of Varieties to Depart Indefinitely from the Original Type. Useful variations will tend to increase, unuseful or hurtful variations to diminish. Changes in species are not adaptations to their environment. Instead, some qualities of an individual may allow it to outlive others [Survival of the fittest]. Charles Darwin (1809-1882), On the Origin of Species. Used own observations, understanding of embryological and physical similarities among animals, their geographical distribution, geological record. Also referred to co-adaptation between two species and a study of artificial selection/selective breeding. Species do not arise independently; but are rather descendents of other species.
Darwin’s challenge: Why do new characteristics not get blended?Answered by the Modern Synthesis (Genetic Mechanisms, Observation) Evolution is gradual: small genetic changes, recombination ordered by natural selection. Natural selection is by far the main mechanism of change; even slight advantages are important when continued. What gets selected is the phenotype in its surrounding environment.
Types of selection in a population with a distribution of phenotypes
Concepts Emerging Following the Modern Synthesis Large-scale geophysical events influenced evolution. Origin of the eukaryotic cell: Symbiosis with bacterial and archaean cells, which gave rise to compartmentalized structures. Tree of life- Now routine Evo-Devo Fossils- Feathered dinosaurs and flatfish Point mutations, gene duplication, horizontal gene transfer
Development consists of growth, differentiation, and morphogenesis Organism development: Process of progressive changes, taking on the successive forms that characterize the life cycle. In some cases, development only ceases with death. - Growth (increase in size): Cell division or cell expansion - Determination (Allocation of destiny). Differentiation: Specialization of cells. - Morphogenesis: Shaping of the multicellular body and its organs.
Endless Forms Hox genes control development along the anterior–posterior axis
Development uses the same sets of genes throughout the animal kingdom
Evolution: Changes in expression patterns of developmental genes
Non Equilibrium Processes Can Create OrderWith ‘Biological’ Characteristics Bénard Instabilities (1900) Set up a layer of liquid, e.g. water, between two parallel planes When temperature of top and bottom planes is equal At a specificT hexagonal convection cells ofcharacteristic dimensions appear. Phenomenon depends on ascending and descending currents (amplified by buoyancy), opposed by fluid’s viscosity.
Macroscopic order results from an interplay of close-range intramolecular forces • Self organisation occurs a consequence of being away from equilibrium. • Hot fluid parcel rises, cools, moves sideways, and sinks in a certain direction of rotation. • First cell arises randomly at specific T. Its rotation influences the next cell that forms. • The characteristic dimension of a cell is ~1 mm in a petri dish. • In contrast, the range of intermolecular forces is 10-10 m.
A reaction with spreading and interacting spirals that mimics life
Formose polymerization reaction in aqueous solution can give rise to sugars like ribose and glucose Formaldehyde (methanal) Can form fromCO2 and light Red regions in the spiral arms represent infrared emissions from dustier parts of the galaxy where new stars are forming. Puzzle: Life uses stereospecific molecules. L-amino acids and D-sugars. Is the early history of the creation of life even knowable?
Other Unknowables Undo-able • Unsolvable problems from Euclid’s Elements: • Trisect of a given acute angle; • Double a cube; • Construct of a square of area equal to that of a given circle. Only instruments allowed are the straight edge and the compass. • Exactly solve the three-body problem • However, planets are able to 'compute' their own paths • Explain quantum mechanics in terms of causality Impossible Construct a Platonic solid other than • Tetrahedron (sides are triangle) • Hexahedron (sides are squares) • Octahedron (sides are triangles) • Dodecahedron (sides are pentagons) • Icosahedron (sides are triangles)
What causes differentiation and morphogenesis? • Experiment (1910): Transplant fragments of a newt embryo in different locations. • Redifferentiation • Hypothesis: “Fields" of cells producing organs such as limbs, tail and gills. • Discovery of DNA • All the information for development is in every cell • Master control genes get turned on or off, affecting the developmental fate of a cell • Field notion rejected • But… Now we know that different mutations can cause the same malformations • So they affect a complex of structures as a unit • Rebirth of field?
Much of development is controlled by molecular switches that allow a cell to proceed down one of two alternative tracksDevelopmental biology is essentially about understanding these switches
