selective pressures the making of a species. selective pressure natural selection occurs over...
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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.
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