Transcript Natural and Artificial Selection

Natural and Artificial Selection
(2 mechanisms of evolution)
Natural selection = survival of the fittest
• When the characteristics of a population of organisms adapt over many
generations it’s called natural selection
• Individuals with favourable characteristics survive specific environmental
conditions pass on their alleles to offspring
• There must be variation
within a species for natural
selection to occur
Selective pressure
Selective pressure – an environmental condition that ‘selects’
for certain characteristics in some individuals and against
different characteristics in others
• Selective pressures can be abiotic…
• eg. temperature, colour of surroundings,
water availability, etc.
• …or biotic
• eg. predators, parasites,
resource competition, etc.
Selective pressure
Natural selection…
• …doesn’t anticipate environmental change
• …has no defined purpose/goal
• A trait that at one time/situation has no survival relevance may, at
another time/situation, make all the difference in survival (or vice
versa)
Sickle cell anemia
• Sickled RBCs
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impaired ability to carry O2
poor blood flow
shorter life span
protect against harmful malaria
symptoms
• Healthy RBCs
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carry O2 efficiently
unimpaired blood flow
normal life span
do not protect against harmful malaria
symptoms
• How would selective pressure play a role?
Artificial selection
Artificial selection - selective pressures exerted by humans on
populations in order to increase the frequency of desirable traits
• eg. dog and cat breeds
• Most of the foods we eat are the result of selective breeding
• eg. grains, fruit, vegetables, meat, milk, etc.
Beef cattle
Wild mustard plant
• Wild mustard has been modified (not evolved!) over time by
artificial selection to produce cauliflower, broccoli, cabbage,
brussel sprouts and kale species
Corn & bananas
Artificial selection of food crops
Pros
• Faster growth time
• Increased nutritional value
• Larger yields
• Pest-resistant and drought
resistant
Cons
• Faster grow times = inability
to tolerate poor soil
conditions
• Decreased variation =
inability to respond (adapt)
to environmental change
• Selective breeding MUST be balanced and maintain genetic
variation within the crop so that future adaptation and may
take place
Monocultures
Monoculture – practice of growing a single plant species over a
wide area for many years
• Results in a crop (population) that share all the same
weaknesses and has little potential for future adaptation
• eg. Like living in a city of clones
Gene Banks
• Contain seeds of every plant species
currently known (especially crop seeds)
• The genotypes contained within these
seeds may enable us to help species
survive in present day conditions
Try this…
• Selective breeding activity