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What Darwin Never Knew How Genetics is Altering Evolutionary Thought 1 of 9 © Boardworks Ltd 2009 The Tree of Life in the 1830’s 2 of 9 © Boardworks Ltd 2009 Tree of Life 3 of 9 © Boardworks Ltd 2009 Modern Tree of Life 4 of 9 © Boardworks Ltd 2009 Question • What do these trees tell you about science? 5 of 9 © Boardworks Ltd 2009 Peas 6 of 9 © Boardworks Ltd 2009 Historical Development The Monk and his Peas. • 1850s Gregor Mendel interbred peas and kept track of their physical traits. • In certain traits he found specific ratios based on the way he interbred the plants. 7 of 9 © Boardworks Ltd 2009 Historical Development • This was the first step in the discovery of genetics. • If Mendel discovered genes as the inherited variation in the 1850s, why didn’t Darwin include this in On the Origin of Species? Darwin Published in 1859 Mendel’s ideas not popular until early 1900’s 8 of 9 © Boardworks Ltd 2009 The Gaps in the Darwin’s Knowledge • How do inherited traits or adaptations pass from one generation to the next? • Variation extremely important! What is the source? 9 of 9 © Boardworks Ltd 2009 10 of 9 © Boardworks Ltd 2009 Historical Development Birth of Genetics • Early 1900s Thomas Hunt Morgan bred fruit flies and studied mutations. • Mutations do not always create a new species as had been suggested. • Source of the variation that Darwin suggested in his original proposal! 11 of 9 © Boardworks Ltd 2009 Historical Development • It took well over 50 years for scientists to popularize and identify the inherited variation that Darwin discussed in his book. 12 of 9 © Boardworks Ltd 2009 13 of 9 © Boardworks Ltd 2009 Review • Natural Selection & Evolution act on natural variation of the population • This natural variation comes from differences in DNA sequences. • DNA is the inherited molecule. 14 of 9 © Boardworks Ltd 2009 Differences in DNA Sequences? • Mutations! • Discovery of DNA in 1950 lead scientists to identify what was inherited and how it was effected. 15 of 9 © Boardworks Ltd 2009 DNA and Natural Selection • Found sources of variation. Mutations Gene Shuffling 16 of 9 © Boardworks Ltd 2009 Mutations • These occur randomly in the genetic code. • They do not seek to “help” organisms. • Those that increase an organisms ability to survive and reproduce may be passed on. Fitness? 17 of 9 © Boardworks Ltd 2009 What is a gene pool? The gene pool can be defined as: The total information from all the genes and alleles of the breeding individuals in a population at a particular time. The gene pool’s composition What happens If there is a consistent change in allele frequency? 18 of 9 © Boardworks Ltd 2009 Current Understanding of Evolution by Natural Selection • NOT within one organism! One organism CANNOT evolve biologically. • Happens to a population over multiple generations. • The change is the allele frequency, the time is the multiple generations. Bunny Simulation! 19 of 9 © Boardworks Ltd 2009 Genetic Drift • Natural Selection is NOT the only source of genetic change. • Flip a coin…what are my chances? • Chance events associated with survival and reproduction not directly effected by selection pressures. 20 of 9 © Boardworks Ltd 2009 Genetic drift 21 of 9 © Boardworks Ltd 2009 Population bottlenecks A population bottleneck occurs when a large, genetically diverse population is drastically reduced by a catastrophic, non-selective event, such as a volcanic eruption. Limiting Factor? The total genetic diversity of the few survivors is likely to be much lower than that of the original population. The cheetah population has an exceptionally low genetic diversity. This is thought to be due to a very narrow bottleneck, where only a single family group survived the last ice age. 22 of 9 © Boardworks Ltd 2009 The founder effect 23 of 9 © Boardworks Ltd 2009 Introducing the Hardy-Weinberg principle The Hardy-Weinberg principle is a mathematical model used to calculate the allele frequencies of traits with dominant and recessive alleles. The model assumes that the population: is large has random mating is experiencing no selection has no mutation, emigration or immigration. If these assumptions are met then the allele frequencies of the population will remain stable over time. 24 of 9 © Boardworks Ltd 2009 Factors affecting the gene pool 25 of 9 © Boardworks Ltd 2009 Types of selection Selection causes some traits to survive and spread, while others are lost. A selection pressure determines which traits are successful. There are three types of selection: disruptive, stabilizing and directional. Starting population has a normal distribution of traits. number of individuals Selection can be represented using graphs showing the distribution of individuals with a particular trait. mode 26 of 9 trait © Boardworks Ltd 2009 Types of selection Selection can cause the mode and/or distribution to change. mode number of individuals mode number of individuals number of individuals mode trait disruptive Selection pressure toward the extremes creates two modal values. 27 of 9 trait stabilizing Selection pressure toward the center increases the number of individuals at the modal value. trait directional Selection pressure toward one extreme moves the mode in this direction. © Boardworks Ltd 2009 Selection pressures 28 of 9 © Boardworks Ltd 2009 Humanity as a selection pressure Human activity provides some of the strongest selection pressures in the world today. The widespread use of antibiotics has exerted a very strong selection pressure on bacteria. Any that can survive exposure to antibiotics can rapidly divide and produce a resistant population. MRSA is an example of an antibiotic resistant bacteria. What are the implications of the evolution of antibiotic resistance for humans? 29 of 9 © Boardworks Ltd 2009 Inbreeding and artificial selection In artificial selection humans decide which members of a population will breed. This allows the alleles for desirable characteristics to be maintained in the population and others eliminated. This technique is used by farmers to produce animals and plants with a high yield. Artificial selection can lead to inbreeding, which reduces genetic diversity. This can increase the risk of a disease affecting the whole population. 30 of 9 © Boardworks Ltd 2009 Convergent Evolution • unrelated species become more and more similar in appearance as they adapt to the same kind of environment 31 of 9 © Boardworks Ltd 2009 Divergent Evolution • the process of two or more related species becoming more and more dissimilar. 32 of 9 © Boardworks Ltd 2009 Coevolution • See Clip 33 of 9 © Boardworks Ltd 2009 Coevolution • joint change of two or more species in close interaction – Predators and their prey sometimes coevolve – parasites and their hosts often coevolve – plant-eating animals and the plants upon which they feed also coevolve – plants and the animals that pollinate them 34 of 9 © Boardworks Ltd 2009