AP bio - Unit 7 (Natural Selection)

Natural Selection

Process by which organisms having adaptations suited for a particular environmnet have a greater chance of survival and reproduction — pass their genes to subsequent generations (Biological Fitness)

Biological Fitness

Reproductive Sucess where individuals survive and can pass their genes to next geneerations

Evolution

Change of genetic makeup of a population over time.

Several conditions must be met for evolution by natural selection

1) Competition

There are competition between limited resources (food, mates, space, etc..)

• Differences in phennotypes will determine how competitive an organism is

• Darwin’s theory of Natural Selection: Competition for limited resources results in differential survival among organisms

2) Favorable Phenotypes

Favorable phenotypes improve chances of survival

• Mutations/sexual reproduction increase variation within populations

3) Evolutionary Fitness

Evolutionary fitness is measured by reproductive success

• Due to selection, traits of individiuals that have more reproductive success will become common in populations

  • Reproductive success/heritabillity of adaptations contribute to evolutionary fitness

4) Ecosystem Stability

Ecosystem stability determines the rate and direction of evolution

• Biotic (living e.g. plant, animals, bacteria) and abiotic (sunlight, water, soil, temperature) environments can remain more or less stable

• Populations are less likely to evolve in stable environments

• Unstable evironment = faster rate of evolution

  • Genetic variation can depend on how much the environment flucturates.

Genetic Variation

Genotypic and phenotypic differences between individuals in a population

• Leads to different adaptations among organisms

• Natural selection acts on phenotypic variation in populations

Due to natural selection, organisms with…

Due to natural selection, organisms with more favorable traits are likely to survive and reproduce

• Changes in the environment (selective pressure) can lead to some phenotypes with increased or decreased fitness

What increases the probability of survival among populations of organisms in a changing environment?

Genetic Variation increases the probability a populaion of organisms will survive in the changing environment

• One of the phenotypes may be better suited for the changed condition

Changing environments introduce…

Changing environments introduce different selective pressures on populations

• Individual’s fitness is relative to environmental condition

• Phenotypes selected for can be selected against when environmental conditions change and vice versa.

  • Any phenotypes that decrease or increases the chances of survival and reproduction negatively or positively impact fitness.

Example of fitness: DDT resistance in insects

Due to natural variation in populations, some insects are resistant to DDT. Resistant insects are not killed by DDT, survive, and pass down their resistant genes to their offsprings. Overtime, the entire population of insects become resistant to DDT.

Variations can also be evident in…

Variations can also be evident in cellular and molecular level including molecular structures and types of moleclues —- Increases fitness in an organism

• E.g. Chlorophyll moleclues vary within plant cells — Different types of chlorphyll capture light energy of different wavelengths (greater flexibility to absorb incoming wavelengths of light used for photosynthesis).

Artificial Selection

Process by which humans select desirable traits in other species and selectively breed organisms with the desired traits

• Results in unatural phenotypes

• Can contribute to genetic diversity or less of it

• Humans affect diversity within the population through (artificial selection) breeding plants and animals and selecting desirable traits.

Example 1 of Artificial Selection: Dog Breed

Hundreds of dogs have been bred from a single wild species (e.g. wolf) as a result of selective breeding

Example 2: Brassica Plants

Different parts of the Brassica Plants have been developed by human selection to produce at least six diverse vegetables: Brocoli, cauliflower, cabbage, kale, etc..

Depending on which traits are selected for and how often they’ve selected…

Depending on which traits are selected for and how often they’ve selected, the genetic diversity of the population can change over time

What is evolution and what does it contribute to

Evolution is a random change in an organism´s genome

• Alternation in DNA sequence

• Contribute to changes in the genetic makeup of a population over time

• creates genetic variation

• Provides new phenotypes that contribute to evolution by natural selection

Genetic Drift and What are two types?

Random change in the frequency of a particular allele in the population

• Nonselective process that occurs in small populations

• Bottle Neck and Found effect

Founder Effect

Random Process that reduces genetic variation within a small population due to seperation of a large population

• Cause by migration or geological events (e.g. catatrosphes)

• Genetic makeup of the founder population is not equal to the original population

Bottleneck Effect

Large, diverse populations reduced to small populations due to diasters

• Contributes to genetic drift

Migration/Gene Flow and its significance

The movement of individuals (migration) between populations causing an exchange of alleles (gene flow) between populations

• Introduction of new genes = increases genetic variation

• Continued migration between population reduces genetic diversity between populations over time

What is fitness relative to?

Fitness is relative to specific environmental changes

• As conditions change, fitness change

• Different phenotypes can be selected for or against according to changes in the environment

• Evolution cannont occur if there is no genetic variation within populations

What are the 5 conditions that must be met for being in the Hardy-Weinburg Model

Hardy-Weinburg is a model for describing and predicting allele frequencies in a non-evolving population (frequencies of alleles and genotypes stay the same generation after generations)

5 conditions include:

1) Large populations - No genetic drift

2) Absence of migration - No gene flow

3) No net mutation - No genes are modified, deleted, or duplicated.

4) No Random Mating - No sexual selection

5) Absence of selection - No natural selection

These conditions are rarely met, but they provide a valuable null hypothesis

Which equation is used to determine genotype or phenotype frequencies of individuals in a population? Which equation is used to determine the frequency of a particular allele in a population

p² + 2pq + q² = 1 (genotype/phenotype frequencies of individuals in population)

p + q = 1 (frequency of a particular allele in a population)

What is life organized in? (hint 3 domains)

• Life is organized into 3 domains: Bacteria, Archaea, and Eukaryotes

• All 3 domains share a common ancestor in distant past (e.g. animal and fungi are related)

What are some (3) evidence that support common ancestry among domains?

• DNA and RNA store/transmit genetic material

• Transcription and translation are universal processes

• Same 20 amino acids make up proteins

• Glycolysis is used to produce ATP

An example of an organism sharing common ancestry with another organism

Whales: The fossil of the basilosaurid whales (40 million years ago) have a nostril opening like whales and dolphins but in different areas

What is Relative Dating?

Determines if something is older or younger than something else (fossil-layer based measurement)

• Stratigraphy - Lower layers are older than upper layers

• Fossils - Uses fossils of known spieces to correlate rock layers

What is Absolute Dating?

Determines the actual numerical age (actual age/number measurement)

• Measures the decay of radioactive isoltopes (parent/daughter elemements) at a known constant rate (half-life)

• Radiocarbon Decay: For organic materials up to 50,000 years old, measures carbon 14 decay

Evidence #1 for common ancestry among all Eukaryotes: Membrane-bound organelles

Chloroplasts and mitochondria have structural similarities:

• Double membranes

• Circular genomes

• Ribosomes

• Endosymbiotic Theory

What are the differences in nucleus between prokaryotes and eukaryotes? What is one thing they are similar in terms of genetic material and/or DNA?

Eukaryotes

• Linear Chromosomes

• Chromosomes made up of tightly coiled DNA with histone proteins

• Found in Nucleus

• Genome is larger

Prokaryotes

• Singular circle chromosomes

• Genome in cytoplasm

• Genomes are smaller

But both function as storing, replicating, and transmitting genetic information through transcription and translation processes.

Evidence #3 among ONLY Eukaryotes: Introns

Introns are common among all eukaryotes

• RNA processing removes introns prior to protein synthesis

• Does not code for proteins

Evolution is an…

Evolution is an ongoing process in all living organisms

• Population of orgaisms continue to evolve

Cause #1 of Species´ evolution: Genomic changes

Changes in DNA

• Gene mutations

• Chromosomal mutations

Cell Division

• Sexual reproduction increases genetic diversity

• Independent Assortment

• Crossing Over

#2 of Species´ evolution: Environmental Disruptions

• Suddent changes in the Environment —— Changes in Alleles and/or gene frequencies within a population

• New selective pressures can result in changes in frequency of certain adaptations in a population

What is an evidence of continued evolution?

Continous change in fossil records is evidence of continued evolution

• New fossils mark changes in the environment

• Transition fossils show evolutionary changes as one group evolves into another

Evolution of resistance to chemicals can become evident though natural selection

• Mutations result in resistance

• Resistant organisms can be selected for under conditions where the trait is advantegous

• Frequency of resistance can increase within a population over time if the trait continues to provide better fitness

Pathogens evolve and cause emergent diseases

• Pathogenic genome experience high mutation rates — increased diversity

• Pathogens are chemically compatible with the host

  • Pathogens co-evolve with the host

  • Presence of pathogens can change the phenotypes selected for or against in the host population

What is a phylogenic tree?

A branched diagram that show evolutionary relationships amongst species

• Phylogenic tree can show changes over time calibrated from fossils or moleclue clock

  

What is a Cladogram

A Diagram used to show evolutionary relationship amongst spieces

• A clade includes any group on a cladogram sharing a common ancestor

Are shared characteristics present in more than one lineage? What do they indicate?

• Shared characteristics are present in more than one lineage

• Shared, derived characters indicate common ancestry

• The out-group represents the lineage least closely related to other organisms

Phylogenetic trees and cladograms can indicate speciation has occured.

• Nodes is where two lines meet — represents the most recent common ancestor

• The root represents the common ancestor of all species on the phylogenic tree or cladogram

• Orientation of phylogenic trees or cladograms can be horizontal or vertical

• A node can be rotated

Construction of the phylogenic trees and cladograms include:

• Morphological similarities from fossil or living spieces

• DNA and protein sequences similarities

  • Molecular data provide more accurate and reliable evidence

• A derived characteristic is a trait in a recent species, having evolved from ancestral traits

Mechanism of Speciation: Allopatric

Physical, geographic barrier that splits a population, causing them to evolve independently due to environmental pressures of genetic drift

• e.g. Squirrels on opposite sides of the Grand Canyon becoming distinct species

Mechanism of Speciation #2: Sympatric

Reproductive isolation occurs without physical seperation but through genetic differences, behavior, or niche specialization (e.g. an organism eating a different source of food than another one)

• e.g. Apple maggot flies diverging into new species based on host tree preference (hawthorn vs. apple) in the same area

Reduced Reproduction and Gene Flow: Prezygotic Barriers

• Habitat Isolation

• Temporal (time) isolation

• Behvaioral isolation

• Mechanical (anatomical) isolation

• Gametic (sex cells) isolation

Postzygotic Barriers

Prevents hybird (cross between two DIFFERENT spieces) from developing into a viable, fertile adult:

• Genes of different parent spieces may impair the hybird’s development

• Chromosomes of parents may differ in number or structure

• Meiosis in hybirds may fail to produce normal gametes

The ability of a population to respond to __________________ is influened by _____________. Spieces and populations with ______________ are at risk for ____________________

The ability of a population to respond to changes in the environment is influenced by genetic diversity. Spieces and populations with little genetic diversity are at risk of decline or extinction

Alleles that are ______________ in one environmental condition may be _____________ in another because of _____________________

Alleles that are adaptive in one environmental condition may be deleterious in another because of different selective pressures.

Evidence that RNA is the earliest genetic material:

• RNA can self-replicate (serve as its own template to replicate)

• RNA contain their own enzymes (ribozymes) which can catalzye chemical reactions

• RNA primers: DNA replication needs RNA primers before it begans, indicating that RNA came first and DNA evolved after

• Many viruses use RNA as their genetic material; indicating that RNA genomes are functional but “old” method of storage

Divergent Evolution

Descendants of a common ancestor evolve independently and uniquely;

• Simpler: Two or more spieces diverge from a common ancestor

e.g. foxes, wolves, and dogs OR elephants and mammoths

Convergent Evolution

Spieces that share a trait but NOT due to common ancestor

E.g. birds, bats, butterflies have wings (shared trait) but they do not share a common ancestor