Microevolution Flashcards
what is microevolution?
is the study of change over time in populations
ie. the change in allele frequency in a population over time
what is allele frequency? instead of thinking about 2 individuals mating when it comes to allele frequency, we should think about..?
is a measure of how often an allele is found in a population
-think about the entire collection of gametes in a population
what is a gene pool a representation of? and what does allele frequency measure in this?
A gene pool is a representation of all the alleles that
are present in a population at a particular time
-measures how often an allele is found in a population
where does genetic variation in a population come from?
- mutation
2. sexual reproduction
what is mutation? at what 3 levels does mutation occur?
change in an organism’s DNA –> Ultimate source of new alleles
- change in chromosome number
- change in chromosomal structure
- change in DNA sequence
what is most genetic variation a result of?
the unique combination of alleles in an individual do to sexual reproduction and the fusion of gametes
what are 3 mechanisms that contribute to shuffling existing alleles into new combinations?
- Independent Assortment
- Crossing Over
- Fertilization
what is independent assortment?
Two equally probable arrangements of chromosomes
what is cross-over?
occurs in prophase of meiosis I and is the exchange of genetic material between two homologous chromosomes non-sister chromatids that results in recombinant chromosomes during sexual reproduction
what is fertilization, and how does it relate to genetic variation?
is the fusing of gametes (sperm and egg)
- Any of the eggs can be fertilized by any of the sperm
- the random nature of fertilization adds to the genetic variation arising from meiosis
what are 3 mechanisms of evolution?
- Genetic drift
- Gene flow
- Natural selection
what is genetic drift? is this process random or not?
-Mechanism of evolution that results in random
fluctuations in allele frequency from one generation
to the next
-Process is completely random
-Chance event causes allele frequencies to change
from one generation to the next
what are 2 examples of genetic drift?
- Founder Effect
- Few individuals become isolated from larger pop.
- Smaller group establishes new population with gene pool that differs from source population - Bottleneck Effect
- Sudden change in environment drastically reduces the size of a population
what kind of populations does genetic drift have a significant impact on? why?
- small populations
- Can lead to loss of genetic variation
- can result in population changing over time (evolving) but NOT adapting to its environment
what is gene flow? is this process random or not?
-the transfer of alleles into or out of a population due to movement of fertile individuals or their gametes
-This process might be completely random or some
individuals may be more likely to move than others
-Alleles exchanged between populations, so tends to
reduce genetic differences between populations
what new thing can gene flow introduce to a population? what happens when this new things is introduced?
-new allele(s)
-Once a new allele is introduced natural selection may
cause that new allele to increase or decrease in the
population
what is natural selection based on? what does natural selection act on? what are 3 requirements for natural selection to occur?
- Based on differential success in survival and reproduction
- Natural selection acts on individuals not on alleles
- Variation –> Individuals in population exhibit variations in their heritable traits
- Heritability –> can be passed on to offspring
- Differential success –> When selection is occurring some phenotypes in a population do ‘better’ than others
-Phenotypes differ in their relative fitness in a
particular environment
-Those with traits that are better suited to their
environment tend to produce more offspring than
those with traits that are less well suited
what is “fitness”? what are the 2 components to fitness?
the ability of an organism to survive and reproduce, and thus contribute offspring to the next generation
- Survival to reproductive age
- Mating success
what does natural selection do to allele frequency? what kind of evolution does natural selection cause? what is it?
Results in change in allele frequency in population
-adaptive evolution –> evolution that results in a better match between organisms and their environment
what are the 3 ways that Natural selection can alter the frequency distribution of heritable traits?
- directional selection
- disruptive selection
- stabilizing selection
what is directional selection?
- Occurs when conditions favour individuals exhibiting one extreme of a phenotypic range
- Shifts frequency curve in one direction
eg. on a scale of white to black mouse, black fur is favorable, so white/light fur mouse die out
what is disruptive selection?
- Occurs when conditions favour individuals at both extremes of phenotypic range over individuals with intermediate phenotypes
- makes frequency curve bimodal
eg. on a scale of white to black mouse, black fur and white fur id favorable, so brown fur dies out
what is stabilizing selection?
- occurs when conditions act against both extreme phenotypes
- Favours intermediate phenotypes
- Reduces phenotypic variation in a population
-eg. no white or black mice, only medium brown
what are some barriers of natural selection?
- Selection can only act on existing variation
- Evolution is limited by historical constraints
- Adaptations are often compromises
