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Selective Pressures The making of a species Selective Pressure • Natural Selection occurs over successive generations • Evolution works on a species level by describing how the species attains the genetic adaptations that allow them to survive in a changing environment. Special Note • Without a changing environment , neither evolution nor natural selection would occur. Genotype Fitness • Are the genes present in a population best suited to allow the population to continue to reproduce? Types of Pressure • • • • Physiological Stress Predation Competition Luck Geologic Isolation • Geologic isolation creates a unique situation that often forces evolution to occur through speciation • The Galapagos Islands offer the best example of this phenomenon • Ring Species • A modern example of speciation through geologic isolation. Case Study • Good Trait? Bad Trait? • Congenital condition known as myotonia congenita • Causes the goat's muscles to tense up when the animal is startled and don't immediately relax. • The gene called CLCN1 (Chloride Channel 1). Under normal conditions • The animal's eyes and ears relay the perceived threat to the brain, which then sends an electrical signal to the skeletal muscles , causing a momentary tensing. • This is often referred to as the fight or flight response. Fight or Flight • Just think how it feels to be startled. You'll find your voluntary muscles contract and tighten for a second. This is your brain telling your muscles that the time has come to possibly confront or run away from an immediate threat. • Normally, this tensing is followed by an immediate relaxing of the affected muscles, allowing you to turn and run away from a perceived threat. The Biology of the Condition • Positively charged sodium ions relay the brain's message for the muscle cells to contract. • Negatively charged chloride ions, which CLCN1 affects, tell the muscle cells to relax. • Mytonia congenita results in an abnormal channel of chloride ions, which throws this relationship out of balance. The Question? • What is the Genotype Fitness of the fainting goat in the wild? • Types of selective pressure? – – – – Physiological Stress Predation Competition Luck Would these goats survive in the wild? • Artificial Selection • In fact, they would not survive in the wild. • Bred as pets • Used by goat herders as bait animals for predators.