BIOLOGY 1M03 Lecture 2: Lecture 2 - Natural and Artificial SelectionPDF

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7 Feb 2016
Natural and Artificial Selection
January 7/2016
From last class:!
In order for natural selection to occur you need: variation that is heritable, and influences fitness.
If certain heritable characteristics lead to increased success in producing offspring, then these
traits become more common over time.
Artificial selection
-artificial selection: is a form of selection where humans drive the course of evolution
-repeating this process over generations results in changes in the characteristics of
domesticated population over time
-changes the phenotype over time
-humans choose who is the fit species
types of corn
cows (cows make more milk and over many generations we have selected the types of
cows that make the most milk)
-is it possible for humans to facilitate artificial selection on humans? - possibly, not intentionally
-example of artificial selection with width of flowering stalk
before artificial selection most plants have a small stalk
after one cross of wide stalked individuals, the average stalk width of progeny is lightly
eventually average phenotype is dramatically shifted
the phenotype is the outward appearance/observable features of an organism
-How fast can artificial selection occur? Depends on:
how many genes influence the phenotype
-ex. if there is only one gene then artificial selection will occur faster, if there are 20 genes
it will take much more time
how much the phenotype is control by environmental factors
-ex. you have a body type like your parents, but what you eat, your exercise and lifestyle
also affects your body type
-How far can artificial selection go (how big, how small, how much)? Depends on:
-whether there are deleterious consequences (trade-offs) of artificial selection
-the limits of the available genetic variations
Unintended Artificial Selection
-Example: big horn sheep
-hunted, you can pay to shoot them
-hunters shot the biggest and strongest individuals
-the size of the male has been declining and the age of reproduction is declining
-between 1971-2003, the size and weight of these animals declined; additional males are
booming reproductively active early so that they have offspring before they are big and get
-thus the effect of trophy hunting was to reduce the quality and number of trophies
-example: cod
-the average size of atlantic cod is much smaller
-which animals die in ecosystems without human predation
-the small old dying ones
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