Exam 6

Modes of Selection on Quantitative Traits

• DIRECTIONAL SELECTION
• --fitness increases or decreases with trait value
• --changes mean value
• --reduces variation
• --increasing linear graph
• STABILIZING SELECTION
• --intermediate trait value with highest fitness
• --mean value does NOT change
• --eg: birth rate of humans (mortality around birth)
• -- outcome of two directional selections
• bell curve
• DISRUPTIVE SELECTION
• --extreme trait values have HIGHEST fitness
• --mean value does not change
• --increases variation
• --could be in different environments

Oxygen Experiment

• keep same sized flies in a tank with minimal oxygen.
• -- measure body size over time in generations
• keep same sized flies in atmospheric air
• -- measure body size over multiple generations
• control: the oxygen level in greenhouse ( helps to compare and contrast phenotypic plasticity)
• Experiment: Put some fruit flies in 20% oxygen tank for generations and put others in 50% oxygen tank
• --allow multiple generations to produce
• --switch environments for flies
• ---weigh over generations and notice genetic change or not

Dover Trial

• First direct challenge in the US courts testing a public school district policy that required the teaching of intelligent design
• Intelligent Design: life is too complex to be random, so it must be a deliberate creator.
• -- claimed to be backed by science
• -- it is not science because it is a religious argument: a form of creationism which lacks empirical support and offers no testable hypothesis

Evolution of Complex Traits

• Complex traits can evolve over time via export/ secretion, adhesion, motility
• --each step adds functionality and increases fitness
• --eg: bacteria flagellum function changes during exaptation. Flagellum is "jurry rigged" from existing and duplicated parts

Evolution of the Eye vs. Bacteria Flagellum

• Flagellum has stepwise evolution that increases fitness and can change function( exaptation)
• -- remove any part and loss of function
• Eye of evolution: function remains the same. Evolves from primitive version of the eye.
• -- remove any part and it should still function

Vertebrate Eye and Imperfect Evolution

• vertebrates developed Inverse retina
• --photoreceptors pointing away from light
• --no convincing functional reasons why we have "inverse retina"
• --result of developmental constraint to show evolution isn't perfect
• --squid have correct "everse" retina

Homology and exaptation

• homology: similarities due to common ancestry
• --eg 5 digit limb of tetrapods--pentadactyl
• --proven no reason to need exactly 3 fingers
• eg 2: homology of flagellum to Type 3 Secretion Systems
• --both evolved from common ancestor
• --flagellum could've evolved from T3SS
• T3SS could have evolved from flagellum
• Exaptation: trait shifting function during evolution
• --eg: feathers evolved for thermal regulation

Creationists Views on Eye and BF

• the vertebrate eye is decsribed as a " bad design"
• --vertebrate eyes are very complex, how could it possibly come
• from simpler eyes, or "what good is half an eye"?
• --randomness in evolution not accredited for creating something so complex
• --EXPLAIN: When we look at living things today though we see a range of different eyes
• in use, from the simple to the complex - each is functional. eg: Shell Mollusk and squds
• bacterial flagellum: number of separate interacting parts,
• flagella not viable if missing any of them, how could this possibly evolve?
• --EXPLAIN: There is no single "The" bacterial flagellum, different species have
• flagella with different structures and combinations of proteins,
• proof that different structures are viable.