UNIT 7: NATURAL SELECTION

Define evolution

the change in genetic makeup of a population over time

State the theory of natural selection

The process by which organisms having adaptations suited for a particular environment, have a greater chance of survival and reproduction, thereby passion the adaptations to subsequent generations.

What are the conditions for evolution?

• Traits are often heritable

• Offspring show variety in their heritable traits

• More offspring are produced than can survive; leading to competition for limited resources

• The phenotypes that are better suited to the current environment improves the population’s chances for survival

• Organisms with adaptations have better chance for survival and therefore reproduction, so over time, these adaptations increase in the population

What is evolutionary fitness?

the ability of an organism to survive and produce fertile offspring

Explain how the rate and direction of evolution is determined

The stability of the ecosystem determines it bc an environment can experience major disruptions and change quickly forcing the rate of evolution to increase otherwise the population dies out. Environments that change slowly over time show populations that are less likely to evolve and remain stable for a long time

What does natural selection act on?

Phenotypic variations in populations where the more favourable traits are more likely to survive

Define selective pressure

any biotic or abiotic factor that influences survivability

Examples of selective pressure

• disease

• predation

• climate

• food availability

Define individual fitness

relative to the environment, phenotypes can be advantageous in one environment and disadvantageous when conditions change

What are the three main types of selective pressure?

1. directional selection: conditions favour on extreme of the trait, shifting the frequency curve to one direction

2. stabilizing selection: conditions favour the intermediate of the trait; the extremes of the trait arent well suited leading to specialization and decreases variation

3. Disruptive selection: causes divergence within species which results into specialization for each branched group. Conditions favour individuals at both extremes over intermediate phenotypes leading to further speciation

Examples of directional selection:

• antibiotic resistance bacteria (to prevent use broad spectrum antibiotics)

• peppered moth

Examples of stabilizing selection:

• bird clutch size

• birth weight of babies

Examples of disruptive selection:

• darwin finches

• rabbits

• skunk

Define artificial selection

the process where humans pick traits in other species and selectively breed them with individuals with desired traits; used as evidence for evolution

What is convergent evolution?

the process by which similar selective pressures in an environment select for similar traits in different populations or species over time.

What are the two types of convergent evolution? describe them briefly with examples

• Analogous structures; similar function but different structure, shows different ancestry; examples; flippers, streamlined bodies in vertebrates, wings for flight

• Homologous Structures; same anatomical structure, different function, shows that they evolved from the same ancestor; example: arms/hands of humans/wings of a bat/leg of a cat/flipper of a whale

Explain a genetic drift

A genetic drift occurs on chance, it is when small populations “ drift away” from the original allele frequency by chance. Eg: founders effect and bottleneck

Describe what the founders effect and bottleneck evolution is

• Bottleneck is when there is a severe reduction in a population size because of some kind of disaster or predation, reducing the diversity of the population; example cheetahs have zero differences with each other and are basically twins

• The founders effect is a random process that reduces genetic variation within a small population due to separation from a larger population; example: Amish colny in pennsylvania having 1:14 dwarfs bc of 30 amish who left germany in 1720

Describe Gene migration/gene flow

Gene migration is another random event that drives evolution. This is where the movement of individuals between populations cause an exchange of alleles between populations, altering the gene frequencies. As new genes get introduces, there is more genetic variation. Example: half vietnamese/half american during the vietnam war

List the processes that lead to evolution

1. Mutation

2. selection: directional/ stabilizing/disruptive

3. Genetic Drift: bottleneck/ founders effect

4. Gene migration:

Define population

a group of interbreeding individuals of the same species (can reproduce and make fertile offspring who can also reproduce) in a common area

What mechanisms change gene frequencies?

mutations and genetic drift

What are the five main mechanisms that change gene frequencies— leading to evolution?

1. Changes in DNA - gene and chromosomal mutations

2. Cell division - s3xual reproduction increases gamete diversity, recombination and crossing over which is the shuffling of genetic material during meiosis

3. Environmental disruptions - sudden changes in the environment leads to natural selection, causing differential reproduction, allowing more of a certain gene to move on to the next generation

4. Reproductive isolation - lead to changes in gene frequency due to different environmental pressures on the isolated population

5. Chance - mainly in small populations, random events can affect gene frequencies

What is the Hardy-Weinberg model?

It is the model for describing and predicting allele frequencies in a non-evolving population.

What is the Hardy-Weinberg Law?

the frequencies of alleles in a population will remain constant unless acted upon by outside forces

What are the five conditions for Hardy-weinberg equilibrium?

1. Large population (no genetic drift)

2. No migration (no gene flow)

3. No mutations

4. Random mating (no s3xual selection based on traits)

5. No natural selection (all offspring must have an equal chance to pass their genes)

THESE CONDITIONS ARE NEVER MET IRL BUT PROVIDE A GOOD NULL HYPOTHESIS

What are transition fossils?

Fossils that show evolutionary change as one group evolves into another

Where do we see continuing evolution?

• species resistance to chemicals

• evolution of pathogens

• change in fossil record

Evidence supporting evolution:

1. geographical; characteristics of a land area

2. physical; morphological homologies/ homologous structures and analogous structures and vestigial structures (no use anymore)

3. geological; fossils

4. biochemical; chemical composition of living things

5. embryological; development of similar species follow similar path through gestation

6. mathematical; calculations and statistics of allele frequencies

What are the three things that supports the relatedness of organisms in all domains?

• DNA and RNA are carriers of genetic information through transcription, translation, and replication

• major features of the genetic code are shared by all modern living systems

• metabolic pathways in order to produce ATP are conserved across all currently recognized domains

What are the evidence that eukaryotes have a common ancestor?

1. membrane bound organelles; the chloroplast and mitochondria have a double membrane, circular genomes and their own ribosomes (Endosymbiotic theory)

2. linear chromosomes; found in all eukaryotes; have multiple linear chromosomes made up of tightly coiled DNA wrapped around histones capped with telomeres (noncoding info)

3. genes that contain introns; noncoding sections of DNA that are spliced out during RNA processing stage