What is evolution?
- it is a change in the form and behavior of organisms over time
- a change in the genetic make-up (allelic frequency) of a population over time
What is the Darwin definition of evolution?
the forms of organisms have been modified from their ancestors; one ancestral form can give rise to many
What are the mechanisms of evolution?
- natural selection
- mutation
- genetic drift
- gene flow
What is natural selection?
it is the mechanism by which populations can become better adapted to their environment
- the process in which individuals with certain inherited traits leave more offspring than individuals with other traits.
- over time certain traits are selected for b
What conditions must be met for natural selection to occur?
- varying phenotypes within a population
- must be heritable traits
- organisms with certain traits will reproduce better
- the unequal ability to reproduce and survive will lead to an accumulation of favorable traits over time
What are some examples of natural selection?
- differential predation of guppy populations. How the color of the fish is effected by reproduction and predators
- evolution of drug-resistant HIV
- evolution of long horns in flat-tailed horn lizards
- salamander species in CA
What are mutations?
This is a change in the nucleotide sequence. Most mutations are neutral or harmful. However, sometimes they can give a higher fitness, and then that mutated allele might be selected for over time. Ex. lactose tolerance in adults.
What is genetic drift?
it is a random change in the genetic make-up of a population from generation to generation.
- it is due to chance events
- it is most noticeable in small populations
- consequences: loss of genetic variation or an increase in a rare or harmful allele.
What are the two types of genetic drift talked about it class?
bottleneck events and the founder effect
What is a bottleneck event?
It is a form of genetic drift.
- This is when a population declines (due to climate change, environment, or predators) dramatically and the small remnant of the population does not genetically represent the original population. This new population is gene
What is an example of a bottleneck event?
Cheetahs. They are almost genetically identical because a long time ago climate change killed most of them off. The remaining small population survived, so all the cheetahs present today came from that population that probably had a small amount of variat
What is the founder effect?
this is when a small number of individuals leave a parent population and form a new population. These individuals that left probably have a different genetic make-up then there parents and since they are small they are subject to genetic drift.
What is an example of the founder effect?
Amish. The amish came from a small group of people who founded them. Within that small population a few people had bad alleles and now in the present these bad genes are very prevalent because they have such a small gene pool. They have higher than normal
What is gene flow?
this is the physical flow of alleles into and out of populations due to immigration or emigration. This causes a change in the allelic frequency. Over time the flow will make the two populations more similar because they are sharing genetic information. A
Why is natural selection a mechanism of evolution?
it is a mechanism of evolution because natural selection causes change to occur in organisms. Traits that are unfavorable will be selected out of the population, whereas beneficial traits will be selected for and eventually this creates changes and even k
Is evolution a mechanism of adaption?
Yes, via natural selection. Natural selection helps create organisms that are better adapted to their environment. Essentially created adaption (traits that help survival).
Do all mechanisms of evolution also lead to adaption?
No, because things like mutations and genetic drift are random events that sometimes actually cause traits that hurt the survival chances of organisms. So they do not necessarily create adaption.
What is fitness?
it is the ability of an organisms to contribute to the gene pool of the next generation. It is how many offspring they can produce and how many of those offspring survive.
- the larger the contribution, the better the fitness.
Why is fitness a relative term?
it is a relative term because to figure out fitness you have to compare organisms contribution to the contribution of other organisms of the same species.
What is adaptation?
this is the process by which organisms become better adapted to their specific environment and thus have an enhanced survival and reproduction rate.
What are the three types of selection?
directional selection
stabilizing selection
diversifying (disruptive) selection
What is directional selection?
this is a shift in phenotype of a population in one direction. This is the most common.
What is an example of directional selection?
guppy experiment or pesticides on insect populations
What is stabilizing selection?
this is a selection for the average phenotype (against the extreme phenotypes
What is an example of stabilizing selection?
birth weight in humans. Bigger and smaller babies have health problems, so the normal birth weight is selected for.
What is diversifying (disruptive) selection?
this is the selection of individuals at the extreme ends of the populations. (against the average). This is rare.
What is an example of diversifying (disruptive) selection?
Ex. african seecracker bird. Large and small beaks do well because of food supply and the average sized beaks do not. Selected by inviability of certain food sources
What are selective pressures?
they are any ecological phenomenon that contribute to natural selection in a population.
What examples of selective pressures?
predators, competition because of lack of resources, disease, loss of habitat, global climate change, natural disasters
How is variation generated?
- mutations
- random assortment during sexual reproduction
What is polymorphism?
this is when there are two or more different phenotypes that exists in the same population
What is geographic variation?
this is variation caused in a species by climate, environment, or other geographical conditions.
Why doesnt variation disappear over generation is selection leads to adaption?
- mutations continue to occur creating new alleles
- more organisms are diploid so recessive traits can be masked and remain in populations
- variations can be neutral and so they are not selected for or against (ear shape)
- there are 2 distinct morphs t