E2 - Natural Selection Flashcards
Evolution occurs when…
natural selection acts on the genetic variability of a population
-happens when the environment favours a certain trait over another
-is like why you see higher rates of Sickle-Cell Anemia in countries where Malaria is common (recall this from our mutations lesson in genetics)
Types of Natural Selection: Directional Selection
-occurs when selection favours individuals with a more extreme variation of a trait
- The result is a shift away from the average condition
- This is very common in breeding
-For example, tall giraffe necks or dark coloured pepper moths being favoured
Types of Natural Selection: Stabilizing Selection
occurs when the average phenotype within a population is favoured
-For example, in hummingbirds, medium sized beaks are favoured
- The long beak is a disadvantage because it requires too much energy to carry around
- The short beak is a disadvantage because it cannot reach the food within the flower effectively
Types of Natural Selection: Disruptive Selection
favours individuals with variation at opposite extremes of a trait over individuals with intermediate variations
-For example, if you are a flower which hummingbirds feed upon, a medium sized flower would be a disadvantage
-Large flowers are favoured because the beak is too small to get into the flower well
-Small flowers are also favoured because the beak would be too large to get into the flower well
Types of Natural Selection: Sexual Selection
favours a specific trait because it enhances the mating success of an individual
-This type of selection often leads to males or females within a population evolving appearances or behaviors which are quite different from each other
-You may see this pressure being given by female mate choice or male-versus-male competition
TRUE OR FALSE: genetic makeup of a population can also change simply by chance
TRUE
- When individuals produce offspring, any particular allele is passed on by chance
- The smaller the number of individuals in a population, the greater the impact of random chance
- This can cause a change in the frequency of an allele in the genetic pool, without any selection pressures (it may even lead to the disappearance of particular allele all together)
-Examples: Bottleneck and Founder Effect
Change Without Selection: Genetic Bottleneck
results in a loss of genetic diversity following an extreme reduction in the size of a population
-Based on which individuals survive the population reduction, there may be a huge change in allele frequency
Change Without Selection: The Founder Effect
occurs when a small number of individuals establish a new population
Similar to genetic bottlenecks, there may be a huge change in allele frequency dependent on which individuals establish the new population
Natural selection is a ____________ of evolution
mechanism
bacterial resistance can occur because of….
variations
-may have a better cell wall
maybe have mroe enzymes
genetic drift
changes to allele
frequency as a result of chance; such
changes are much more pronounced in
small populations
Hardy-Wienbrug Principle
in large
populations in which only random chance
is at work, allele frequencies are expected
to remain constant from generation
to generation
Consequences of Human Influence
-commerical fishing–> gene pool being lost by overfishing
-habitat loss–>Populations with little genetic variability are less able
to survive environmental changes and diseases. creates created genetic bottlenecks,
-Selective hunting of prize animals –>* Individuals that exhibit prized traits become less common
in the population.
TRUE OR FALSE: The Hardy–Weinberg principle can be used to identify factors that will result
in evolutionary change.
TRUE
