ANTHR101 Lecture Notes - Lecture 4: Allele Frequency, Panmixia, Microevolution
22 Oct 2018
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From lectures 4,5,6, and 7, placed together to make it more cohesive
Explaining Variation
• Populations evolve by a process known as microevolution
• The change in allele frequency from one generation to another
• Over time, microevolution produces more obvious change in species (Macroevolution)
Sources of Variation
• Mutations are the only source of new alleles
• Sexual reproduction
• Crossing over stage produces almost limitless possibilities (combination of maternal and
paternal DNA from a parent passed onto their child)
• Random mating
• Every allele has an equal chance of being passed onto offspring
• For example, a person would not purposefully mate with someone who has type O blood
• Natural selection acts on this variation by differential reproductive success
• Adaptation
• Any change by which organisms respond to environmental pressure
• Genetic adaptation
• Changes within populations in response to selection pressure
• Occurs over several generations
• Only in populations (not individuals)
• Acclimatization
• A physical response within individuals to environmental pressures
• Takes from a few days to a few months to occur
• Usually reversible once removed from the environmental pressure
• Eg tanning in light skinned people
Types of selection
• Directional
• Physical characteristic moves in one direction over time
• Eg horses growing larger, it was continuously favourable for horses to be larger, so they
continued to increase in size (to a point)
• Stabilizing
• Extremes are selected against, eliminating genetic variation
• Eg birth weight in humans, being too small and being too big were disadvantageous so they
were selected against
• Disruptive
• Extremes are selected
• The middle ground is no longer favourable, but both extremes are favourable
• Usually all three types are at play within a species, but for different traits
