Evolutionary transitions 1-4 . The major transitions in evolution o The Major Transitions in Evolution is a book written by John Maynard Smith and Eörs Szathmáry (Oxford University Press, 1995) o No evidence that evolutionary lineages should increase in complexity in time (bacteria are still bacteria) o However, eukaryotic cells are more complex than prokaryotic cells and plants and animals are more complex than protists This could have been achieved only as a result of a series of major evolutionary transitions o The 8 major transitions are as follows: " Replicating molecules > Populations of molecules " Independent replicators > Chromosomes · RNA -> DNA · Prokaryotes > Eukaryotes · Protists -> multicellular animals, plants, fungi " Asexual reproduction > Sexual reproduction " Solitary individuals > Colonies (eusociality) Primate societies -> Human societies . Replicating molecules > Populations of molecules o Amino acids can be produced from simple inorganic precursors (chemicals diversified & created building blocks for life) Wires cary electric cunene Spark: discharge Gases' Condenser Cooling Water Chemical origin of life: Aming Arts B??ng wader Miller-Urey experiment (1952) mimicked early Earth conditions to create amino acids from water, methane, ammonia and hydrogen. * wzor vapour, ammonti, methane, hydrogen Primordial soup (a solution rich in organic compounds in the primitive oceans of the earth, from which life is thought to have originated) Amino acids can be produced from simpler inorganic precursors in simulated early-life conditions Criticism: early atmosphere hydrogen poor > not high enough concentrations o The chemoton is an abstract model for the fundamental unit of life (Tibor Ganti, 1952). It is the oldest known computational abstract of protocell o The basic assumption of the model is: metabolism, self-replication and a bilipid membrane Outline of the Chemoton membrane M o The metabolic and replication functions together form an autocatalytic subsystem necessary for the basic functions of life membrane- forming system R o Membrane encloses this subsystem to separate it from the surrounding environment waste metabolic system (autocatalytic) genetic system (RNA) Tibor Ganti (1971) nutricients
o Idea of self-contained and living evolutionary unit . Independent replicators > Chromosomes o The table below summarises some differences between prokaryotes & eukaryotes (*see lecture for more) o Benefits of chromosomes: Efficient storage of more Information; Recombination and maintenance of genetic variation; efficient packing of DNA (every human cell contains 1.82 meters of DNA) Prokaryote Nucleoid Plasmids Tightly wrapped DNA to better fit Inside the cell Chromosome 200000 = K Exon Intron Gene Exon Nucleosome DNA Characteristic E.coli genome Human genome Genome Size (base pairs) 4.6 Mb 3.2 Gb Genome Structure Circular Linear Number of chromosomes 1 46 Presence of Plasmids Yes No Presence of Histones No Yes DNA segregated in the nucleus No ===== == Codes for proteins Number of genes 4,288 20,000 Presence of Introns No* Average Gene Size 700 bp 27,000 bp Yes Yes · RNA > DNA o The Chicken and Egg Problem DNA needs proteins in order to form, and proteins require DNA to form, so how could these