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Chapter 15

BIO316 Chapter 15 - Evolution

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University of Toronto Mississauga
Don Mc Kenzie

CHAPTER 15: EVOLUTION  Process of change and adaptation developing new life forms and genetic diversity Theories of Evolution A. Lamarck o Formulated the concept of use and disuse  Organs that are used extensively develop, while organs that are not used atrophy o Theorized that complex species arise from older and simpler species through the accumulation and modification of acquired characteristics o False – now known that characteristics are inherited (not acquired) B. Darwin o Organisms produce offspring – some survive to reproductive maturity o Variations between individuals of a given population exist  Those that provide them with a slight advantage are favourable variations o Those inheriting favourable variations are likely to live longer and produce more  This favourable variations become more common every generation o Known as natural selection – driving force of evolution o Differentiate organism and slowly into new species  Fitness – reproductive success and ability to contribute to the perpetuation of the species C. Neo-Darwinism (the modern synthesis) o Ultimate source of hereditary variation lies in the process of mutation and genetic recombination – some increase chances for survival and reproduction (favourable genes) while others don’t  This is differential reproduction  After many generations, favourable genes will become prevalent in the gene pool (all genes in all individuals in a population at a given time) D. Punctuated Equilibrium o Evolution is characterized by long periods of stasis ‘punctuated’ by evolutionary changes occurring in spurts (as shown by fossil records) o Opposes Darwin’s model which proposes gradual evolutionary changes Evidence of Evolution – drawn from many disciplines A. Palaeontology o Study of the fossil record o Uses radioactive dating techniques to determine the chronological succession of species in the fossil record B. Biogeography o Refers to the distribution of life forms throughout the globe o Darwin observed that many species found on the Galapagos Islands seemed more closely related to species of the mainland than to species of the other Galapagos islands  Suggests that species migrated from mainland to islands and adapted to island environments in isolation from each other C. Comparative Anatomy o Homologous structures are similar in structure and share a common origin  Example: structures found in the forelimbs of mammals – bat wings, whale flippers, horse forelegs, and human arms o Analogous structures share functional similarity but arose from different origins  Example: the wings of insects and birds are both adaptations for flight but evolved from separate lines of descent o Vestigal structures are remnants of organs that have lost their ancestral functions  Example: the tail bone (coccyx) in man D. Comparative Embryology o States of embryonic development in closely related organisms are similar  Means common evolutionary origin  Most similar at the earlier stages o Example: all chordates exhibit certain features as embryos (e.g. gills) E. Molecular Biology o Through comparative DNA studies o ‘Close’ species have a greater percentage of similar DNA than ‘distant’ species Genetic Basis of Evolution  Genetic variations function as the raw material for natural selection o Include mutations (random) and recombination (from sexual reproduction) A. The Hardy-Weinberg Equilibrium o Evolution can be viewed as a result of changing gene frequencies w/in a pop.  Gene frequency is the relative frequency of a particular allele  When the gene frequencies of a population do not change, the gene pool is stable and the population is not evolving o Certain conditions must be met for the genes in the pool to exist in equilibrium  The population is very large  No mutations affecting t
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