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.