natural selection (8.1) (Types of selection and genetic drift) (Evolution) Flashcards
What is natural selection? (what is it effected by and what does it lead to) (what does it create? what does it result in?)
-> The environment favouriting (allowing them to survive longer or reproduce more) certain individuals over others based on their genetic makeup (the traits that they have)
-> Does not occur by chance (fully influenced by the environment)
-> leads to evolutionary (genetic changes) changes within the populations, because natural selection accumlates overtime.
RESULTS IN…
–> major adaptions within the species
–> formation of a new species (speciation)
Evolution pipeline with definitions
Evolution: (Genetic changes of a population over time)
–>
Natural Selection: (Your environment favouriting other organisms more than others, allowing them to pass down more traits/genetic information to upcoming generations, because they reproduce more and they survive more)
–>
Genetic variability: Within a population, animals may be in the same species but are genetically different or hold genetic differences. (My friend and my sister are both humans but are gentically different)
W/O genetic variability, natural selection CANNOT occur.
–>
Genetic mutations and recombination: Mutations = changes in the DNA.
What is selective pressure?
Anything in your environment (either abiotic or biotic) that effects an organism.
—> Any conditions within your environment that can select for certain characteristics of some indivduals and select against different characteristics in other indivduals
–> Influences what traits become rare and what traits are common.
–> Depending on the environment, it results in different patterns of natural selection
What are the 4 types of natural selection and how do they relate/differ from each other?
1) Directional Selection
2) Stabilizing Selection
3) Disruptive Selection
4) Sexual Selection
(Directional, stabilizing, and disruptive, are all environmental based)
(Sexual selection is only related to organisms)
Sickle cell anemia, explain how this is an example of natural selection within humans.
–> Sickle-cell Anemia: A single base mutation in the DNA coding for hemoglobin
–> Humans who are heterozygous for the allele (therefore do not have the condition but carry the trait) are resistant to malaria (Disease)
—> Due to their resistance they have a better chance of suriving than those without the allele, and therefore will repdouce more/pass down their traits more.
HOWEVER:
Where malaria is MORE PRESENT, the sickle cell allele is more present.
–> ie: Africa will have a large presence in sickle cell alleles because malaria is MORE common there
What is directional selection? (Where is it common in?) (An example?) (Describe how the graph would look like)
When the allele frequency shifts to one extreme variation of a trait. (A single shift away from the average condition)
–> An extreme variation of a trait becomes the average/more frequent
Common in..
1) Artifical breeding (Where one trait will be specificalyl bred for)
2) Environmental changes
3) A population that migrates to a new habitat (Environmental change for that population)
ie: Strawberries are selected to be larger and sweeter, (an extreme from the average, medium sized, slight sweet strawberry)
–> “Selected” means bred for, therefore larger and sweeter strawberries are more common.
Graph: A major shift the right or a major shift to the left.
What is stablizing selection? (Where is it common in?) (An example?) (Describe how the graph would look like)
The average phenotype/the trait that is already frequent, remains frequent, therefore it is favoured by the environment and the “extreme variations” of traits get less and less prevelant.
–> Common in unchanging environments (Because if nothing is wrong and you are sucessful, why change or become different?)
Examples:
Birth rate is genetically variable (Different among every person)
–> Because of natural selection, more babies are born at a “medium sized” weight and this gives the babies a better chance of survival.
Graph: Becomes skinner, less extremes of a trait, more “averages”
What is disruptive selection? (Where is it common in?) (An example?) (Describe how the graph would look like)
Natural selection favours two or more variations (Usually the two extremes) of a trait. Therefore the average or the what WAS frequent becomes elimated or a lot less common.
Common in
New environements (regarding resources!)
Example:
Birds move from one island to another, previous island only had medium sized flowers = medium sized birds, now the new island has only small sized flowers and large sized flowers (the two extremes)
What is sexual selection? What are its two ways it can work? (describe) (Does selection selection corelate with survival?)
Sexual selection: The favouriting of any trait that enhances the ability to find a mate and reproduce
-Females Mate of Choice:
–> Sexually dimorphic (Females and males of the same species look SO different, because males need to appear visually appealing to gain female approval)
-> Males evolve to look nicer/more outstanding (Antlers, feathers, etc)
-> Female can choose mates based on behaviours.
–> Certain dances, tricks, etc
LEADS TO DISADVANTAGES:
-> Preditators can find them easily/easier due to distinctive songs or flashy colours
-Competetion Between Males
–> Competetion through visual display (who looks prettier)?
-> Fighting to claim territory (that females are on)
SEXUAL SELECTION = REPRODUCTION (NOT SURVIVAL)
–> (How much more offspring can you produce?)
“Weaker” = males that may live longer, but are NOT reproducing offspring (they are not passing down their traits)
Sexual selection within plants, how does it work?
(Sexual selection favours plants that are…)
-> Colourful flowers
-> Stronger scents
= More attraction to polinators (which allow the plant to reproduce)
–> More plant reproduction = more traits being passed down = contribuiting to more alleles to the NEXT generational gene pool (evolution)
Example of natural selection within humans (Tibetans)
Tibetans an example how different organismsm/groups of organisms within a species can evolved differently from the rest
-> Lives on mountains = high elevation = lower levels of oxygen
–> Low levels of oxygen usualyl causes people to produce more red blood cells (As an attempt to carry/transport more oxygen throughout the body)
–> More red blood cells = BAD, because can cause more blood clots/makes blood thicker
However, tibetans do not have more red blood cells NOR do they have lower oxygen levels.
–> They experienced a “directional shift” where natural selection had favoured indivduals with a genetic mutation that increased oxygen carrying abilities w/o more red blood cells (indivduals that were more efficent in processesing oxygen)
–> Natural selection favoured one extreme of the population.
Can you aquire behaviours by natural selection? (example?)
-Possibily.
(Behaviours = “aqquired traits,” the idea of can you pass down being nice or sporty?)
–> Unsure/most likely not
–> Offspring that look like they have inherited aquired traits is most likely becausr they are exposed to that behaviour at a young age (influenced by their environment)
Can evolutionary changes happen without natural selection?
Yes.
Evolutionary changes = changes in the genetic makeup of a population (without natural selection) = BY CHANCE
–> Not dependent on the “favourite traits” or the environmental conditions (in the way natural selection works: ie stable environments).
-> All evolutionary changes that happen w/o natural selection, will reduce GENETIC DIVERSITY. (Elimination of genes from the genepool)
-> Evolutionary changes without natural selection are more pronounced in smaller population
What is the main way evolutionary change can happen without selection? (What are the two sub categories and how does it relate to the main category)
1) Genetic drift (main category)
ENCOMPASSES
- Bottle neck effect
- Founders effect
Bottle neck effect and founders effect influences genetic drift.
How does genetic drift happen and what does it mean? What is it more drastic in? How do the graphs look?)
-> Changes to the allele frequency (the alleles that are common) in a populations, as a result of chance
–> Natural selection = usually gradual
–> Genetic drift = usually immediate (Why? Usually refers to a whole population experience a large death rate suddenly)
Genetic drift is MORE drastic in smaller populations because there are less alleles to work with, therefore the elimintation of a small amount of alleles will effect the whole population.
Note: This can make a allele that wasnt common very common, and it can make the very common allele disappear entriely.
Graphs:
-> PAY ATTENTION TO THE AXIES
–> Usually a comparasion between a small population and a large population, where the same thing happren to both of them
-SMaller populatiosn will either have a drastic loss or grastic gain in the frequency of a CERTAIN allele
- larger populations will look to remain stable because there is not a big difference/wasnt a big deal (they have alot of alleles to work with)
