GB1Lecture21Macroevolution

GB1Lecture21Macroevolution - I Introduction A Species in a...

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I. Introduction A. Species in a Latin word meaning “kind”or “appearance” B. Speciation - processes where one species splits into two new species C. Microevolution - changes over time in the alleles in a population D. Macroevolution - a broad pattern where species are formed. What is a species? How is a species defined? E. The Biological Species Concept (Ernst Mayr) 1. The biological species concept states that a species is a groups of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations 2. Gene flow between populations holds the phenotype of a population together II. Reproductive Isolation A. Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring 1. Hybrids are the offspring of crosses between different species 2. Reproductive isolation can be classified by whether factors act before or after fertilization B. Prezygotic barriers block fertilization from occurring by: - Impeding mating - Preventing completion of mating - Hindering fertilization if mating is successful 1. Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though may not be isolated by physical barriers 2. Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes 3. Behavioral isolation: Courtship rituals and other behaviors unique to a
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