AP Biology Unit 7

Natural Selection

Mechanism of Evolution by which organisms better suited for their environment survive and reproduce, passing their traits on.

1) Heritable genetic information exists within a population.

2) More offspring are produced than an environment can support. Struggle for survival.

3) Differential reproductive success. Individuals with favourable traits are more likely to survive and reproduce.

Fitness

Measured by reproductive success. Survive and find mates.

Abiotic factors

Environmental constraints.

Biotic factors

Interactions between organisms: predation, competition

Phenotypic variation

Natural selection acts on this. When environments change, selective pressures are applied and organisms with the advantageous phenotype are favoured

Variation in molecules

Molecules within cells control how well it functions, affecting fitness. Variations in enzymes: food source expanded.

Directional selection

One end of the range of phenotypes is favoured, over time the average phenotype of the population changes.

Stabilizing selection

Intermediate phenotype is favoured and extreme phenotypes are selected against. Decrease in genetic diversity as the population stabilizes around the average.

Disruptive selection

Both extreme phenotypes are favoured and intermediate phenotype is selected against.

Sexual selection

Traits that increase the ability to find a mate are favoured, even if they decrease chances of survival.

Artificial selection

Humans select which traits are desirable, and breed those organisms to increase the traits within that population.

Molecular evidence

Comparing DNA, RNA and Amino Acid sequences shows how species are related and have changed over time. The more closely related species are, the more similar the sequences.

Homologous structures

Body parts in different species that have the same underlying anatomy but may serve different functions because organisms had different environmental needs. Come from a shared ancestor.

Analogous structures

Body parts in different species that have the same function but different underlying anatomy because they evolved from different ancestors.

Vestigial structures

Features that once had a function in an ancestor but now serve no purpose.

Fossils

Transitional fossils show characteristics of both ancestral and descendant group. Dated using rh age of the rocks where it was found or the rate of decay of the isotopes.

Biogeographical

Studies the distribution of species and how they adapted to their environments.

Convergent evolution

Unrelated species independently evolve similar traits due to similar environmental pressures.

Divergent evolution

Closely related species develop different traits as they adapt to different environments.

Gene pool

All the genes including their alleles within a population.

Influenced by: Mutations - Importance source of new alleles

Natural selection: Increase of beneficial alleles in the gene pool

Non random mating: changes genotype frequencies.

Gene flow

Movement of alleles between populations due to migration and interbreeding of individuals from different populations.

Reduces genetic difference between populations - counteracts genetic drift and natural selection (prevents a population from adapting to a certain environment)

Genetic drift

Random changes in allele frequencies due to random events

Bottleneck effect

Population size drastically reduced due to disaster. Small, random group of survivors who do not possess all the alleles of the original population.

Reduces genetic diversity as the survivors build a new population.

Founder effect

Few members of a larger population start a new population. New populations gene pool contains alleles of the founders leading to reduced genetic variety.

Common ancestry

Evidence: Linear chromosomes, membrane bound organelles, universal genetic code.

Continuing evolution

Pathogens creating new disease, bacteria obtaining antibiotic resistance, genomic changes (mutations).

Allele frequency

Portion of a specific allele in a population.

Genotype frequency

Portion of individuals with a specific genotype.

Species

Group of organisms that can interbreed and produce fertile offspring

Population

All individuals of the same species living in the same area.

Speciation

Formation of a new species when populations become reproductively isolated. Gene flow stops: populations accumulate genetic differences over time and become distinct species.

Allopatric speciation

Occurs when populations are geographically isolated

Sympatric speciation

Occurs without any geographical barriers

Pre-zygotic

Prevent the formation of a zygote

Habitat isolation

Organisms live in different habitats within the same area, thus not mating.

Ground vs. Tree canopy

Temporal isolation

Different breeding periods/active times.

Behavioural isolation

Differences in mating behaviours prevent selection of each other as mates

Mechanical isolation

Organisms can’t physically mate due to incompatible reproductive structures.

Gametic isolation

gametes are incompatible, no fertilization occurs.

Post-zygotic

Prevent the zygote from developing into a successful and fertile organism

Hybrid inviability

Hybrid offspring fails to develop/survive into adulthood

Hybrid sterility

Hybrid develops but is infertile

Hybrid breakdown

F1 hybrids are healthy but with each subsequent generation they get weaker.

Variation in populations

More genetically diverse populations are able to handle environmental pressures. Populations with little genetic diversity and more prone to extinction.

Early earth

Earth was formed around 4.6 bya, Inorganic materials that were in the atmosphere combined into monomers of biological molecules which then combined to make polymers.

Miller-Urey experiment

Simulation of earths early atmosphere was constructed. After a few weeks, amino acids were found.

Proved that organic molecules (especially amino acids) could be produces from inorganic substances.

RNA world hypothesis

Life began with RNA that could self replicate. RNA can carry heritable information and act as a catalyst for chemical reactions: ribozymes.

Evidence: Ribosomes active site is primarily composed of RNA, and they carry out translation.

hHeterozygote advantage

Individuals with two different alleles for a gene have higher fitness.

Pseudogenes

Nonfunctional segments of dna that resemble functioning genes. Lost coding ability due to mutations.

Punctuated equilibrium

Theory that species experience long periods of stability interrupted by brief evolution

Gradualism

Species evolve slowly and steadily.

Phylogeny

Study of evolutionary history and relationships between organisms

Cladograms

Focus on who is related to who. Branching diagrams representing evolutionary relationships. Branch length means nothing.

Phylograms

Type of phylogenetic tree where the branch length represents amount of genetic change

Chronograms

Type of phylogenetic trees where branch lengths represent the amount time

Nodes

Branching point representing when a common ancestor diverged into new lineages

Clades

Group in phylogenetic tree that includes a common ancestor and all of its descendants.

Branch off nodes

Important: relatedness is not based off how close the tips are but how close the internal nodes are.

Outgroup

least closely related member used as a reference

Ingroup

set of organisms whose evolutionary relationships you’re studying

Shared ancestral

trait present in all descendants of a common ancestor

Old so it doesn’t give enough information

Shared derived

new traits from a more recent common ancestor that are only shared by descendants of that common ancestor

Taxa

Specific groups used to classify organisms (species, genus, class, kingdom)

Sister taxa

Two clades that emerge from the same node