evolution as genetic change Flashcards
How does natural selection work on a single gene trait?
If a gene mutation of an allele creates an advantageous phenotype that makes the species more able to survive or reproduce, then over time, that single gene mutation will proliferate and so will the phenotype (such as big claws on a bear).
In what 3 ways can natural selection work on polygenetic traits?
when a trait is controlled by more than 1 gene the effects could display a range of phenotypes in the form of 3 bell curves: 1. directional selection, 2. stabilizing selection, 3. disruptive selection.
what does a directional selection curve look like? why?
the curve shifts forward due to higher survival and reproduction due to the new adaptive traits for an environmental extreme on one side ( ex. big beaks for big seed distribution)
what is a stabilizing selection curve shaped like? why?
the curve rises in the center because the advantageous traits that evolve can work with environmental extremes from both sides (medium beaks for all sized seeds)
what is a disruptive selection curve shaped like? why?
the curve shapes as an M because the naturally selected traits that evolve work for one group at one environmental extreme and another group from the opposite environmental extreme. (little beaks for little seeds and big beaks for big seeds because there are no more medium seeds )
What else can cause allele frequency change besides natural selection via mutations?
genetic drift
what is genetic drift?
when a species leaves an allele to its decedents just by chance and then it becomes common over time in that population.
what are 2 types of genetic drift?
- bottleneck and 2. founder effect
give an example of bottleneck.
caused by a dramatic circumstance, such as a huge earthquake or deadly virus, that significantly reduces the allele frequency and genetic diversity.(cheetah has reduced genetic frequency)
give an example of founder effect.
when a few individuals from a species colonize on a deserted island. their alleles frequencies may vary from the greater species over time may cause a subgroup within the species with gene frequency changes. (fruit flies in Hawaii)
what is genetic equilibrium?
when the gene pools are not changing in a species/population (if this continues the species will not evolve)
What is the Hardy-Weinberg principle used to determine? How does it determine?
If evolution is taking place. It looks for any skewed percentages in an allele from the Punett square probabilities for a population.
What 5 things can change genetic equilibrium?
- nonrandom mating (ex. only mating with red bellied birds, not yellow bellied) , 2. small population size (bottleneck), 3. mutations, 4. natural selection, gene flow from immigration or emigration (founder effect)
