AP Bio Unit 1: Natural Selection

Gene

The unit of heredity passed from parent to child. They are made up of sequences of DNA arranged at specific locations on chromosomes and contain information for specific proteins which leads to expression of a particular phenotype or function.

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Genotype

An organism’s genetic information.

Phenotype

The set of observable physical traits.

Null Hypothesis

Predicts/assumes that there is NO relationship between the 2 variables and serves as a baseline or default position.

Alternative Hypothesis

Predicts/assumes there IS a relationship between the two variables and the researcher aims to support this.

The 5 Fingers of Evolution

Small Population

Non-Random Mating

Mutations

Gene Flow

Adaptation

The 5 Fingers of Hardy-Weinberg

Large Population

Random Mating

No Mutation

No Gene Flow

No Selection

Hardy Weinberg Equilibrium

When a population is in equilibrium and is not evolving

Gene Pool

Consists of all the copies of all the genes in that population

Allele Frequency

How common an allele is in a population (determined how many times the allele appears in population then dividing by the total number of gene copies)

Hardy-Weinberg Equilibrium Equation

p² + 2pq + q² = 1.0

(p + q = 1.0)

Used to compare the observed vs expected genotype frequencies of a population. If the observed & expected frequencies match, the population is in equilibrium (no evolution) and vice versa (example of calculation attached)

[ p² ] in Hardy-Weinberg Equation

Frequency of homozygous dominant genotype (AA)

[ 2pq ] in Hardy-Weinberg Equation

Frequency of heterozygous dominant genotype (Aa)

[ q² ] in Hardy-Weinberg Equation

Frequency of homozygous recessive genotype (aa)

Macroevolution

Evolution occurring at a large scale over a long time period. This kind of evolution is above the levels of population and is not directly observable (fossils). Often caused by extended microevolution.

Microevolution

Evolution occurring at a small scale over a short time period. This kind of evolution takes place within a species or population and is observable through experimental evidence. It’s caused by mutations, selection, gene flow, and genetic drift.

Increases Variation in the Population

Mutation, Gene Flow, Reproduction

Decreases Variation in the Population

Non-random mating, Genetic Drift, Natural Selection

Mutations

Creates variation by causing a change in the DNA sequence (changes protein structure & function)

Synonymous Substitution Mutations (Silent Mutation)

Does not change the encoded amino acid

Nonsynonymous Substitution (Missense Mutation)

Does change the encoded amino acid

Gene Flow

Movement of individuals and alleles in and out of a population. This causes genetic mixing across regions and can introduce new variation to a population while also reducing differences between the populations.

Isolation

Any barrier that prevents interbreeding between populations, preventing gene flow. Allopatric speciation and sympatric speciation are two types.

Allopatric Speciation

Geographic isolation due to physical barriers.

Sympatric Speciation

Reproductive isolation due to timing of reproduction, behavioral differences, etc (takes place in the same area.

Non-Random Mating

Individuals of one sex mate preferentially with particular individuals of the opposite sex rather than at random. This causes traits that attract mates to be passed on and reduces variation in population.

Genetic Drift

A chance event that causes a change in the population and decreases genetic variation. Bottleneck & Founders effect are two examples.

Bottleneck Effect

An environmental event that leaves only a few survivors.

Founders Effect

When a small group leaves and starts a new colony.

Natural Selection

Natural selection increases the frequency of alleles that improve fitness, helping the fittest organisms survive and reproduce (VIDA: Variation, Inheritance, Differential Survival (fitness), Adaptation).

Stabilizing Selection

A type of natural selection that favors intermediate phenotypes rather than extreme variations. This decreases genetic variation.

Directional Selection

A type of natural selection that favors one phenotype, causing a shift in the population’s allele frequency in one direction. This shifts genetic variation.

Disruptive (or Diversifying) Selection

A type of natural selection that favors extreme variations for a trait over intermediate values. This increases genetic variation.

Phylogeny

The evolutionary history for a group of species based on evidence from living species, fossil record, and molecular data

Node (Branch Point)

Each intersection in the tree which represents a shared common ancestor. It is also a speciation event.

Outgroup

A distantly related group that is used to show how the main group falls in the main tree of evolution

Clade

A group of organisms that include an ancestor and all descendants of that ancestor (a branch on the tree of life)

Taxon

The top/tips of the phylogenetic tree (represents the different species)

Cladograms

A type of phylogenetic tree where branch lengths are arbitrary and do not represent the evolutionary distance or time. They are created by considering the various possible evolutionary pathways.

Paraphyletic

A group that includes the common ancestor and some but not all of the ancestors’ descendants

Polyphyletic

A group that does not include the common ancestor of the group

Monophyletic

A group that includes the common ancestor and all descendants of that ancestor (a clade)

Convergent Evolution

Two species with different ancestors converging to produce analogous structures (species’ appearance becomes more similar over time while remaining genetically different)

Divergent Evolution

Two species with a common ancestor diverging to produce homologous structures (species’ appearance becomes more different over time while remaining genetically related)

Homologous

Same basic bone structure that came from a shared ancestor

Analogous

Separate evolutionary origins but converged due to environment, traits did not come from a shared ancestor

Darwin’s Findings

He proposed the theory of natural selection (but lacked understanding of genetics) and laid the foundation of mechanisms that lead to speciation.

Species

A population whose members can interbreed and produce viable, fertile offspring. Species form when populations are isolated, allowing them to evolve independently.

Prezygotic Barrier

Mechanism that prevents fertilization from happening in the first place (ex: geographic isolation, behavioral isolation, mechancial isolation, etc)

Postzygotic Barrier

Fertilization happens, but there is a mechanism that prevents the hybrid from being fertile and viable or having fertile offspring (morphological differences, gametic isolation, hybrid viability + fertility + breakdown

Geographic Isolation

Species occur in different areas due to a physical barrier (Prezygotic Barrier, Allopatric Speciation)

Ecological Isolation

Species occur in same region, but occupy different habitats so rarely encounter each other (Prezygotic Barrier, Sympatric Speciation)

Temporal Isolation

Species that breed during different times of day, different seasons, or different years (Prezygotic Barrier, Sympatric Speciation)

Behavioral Isolation

Unique behavioral patterns and rituals isolate species (Prezygotic Barrier, Sympatric Speciation)

Mechanical Isolation

Morphological differences can prevent successful mating (Prezygotic Barrier, Sympatric Speciation)

Gametic isolation

Sperm of one species may not be able to fertilize eggs of another species

Post Reproduction Barrier

Prevents hybrid offspring from developing into viable, fertile adults (Postzygotic Barrier, Sympatric Speciation), and could also lead to hybrid breakdown

Hybrid Viability

Genes of different parent species may interact and impair the hybrid’s development

Reduced Fertility

Even if hybrids are vigorous, they may be sterile (chromosomes of parents may differ in number or structure and meiosis in hybrids may fail to produce normal gametes)

Reduced Breakdown

Hybrids may be fertile and viable in the first generation, but when they mate, offspring are feeble or sterile.

Gradualism

Speciation occurs gradually (small changes over a long time)

Punctuated Equilibrium

Speciation occurs in rapid bursts of change mixed with long periods of little or no change

Ring Species

A ring of populations that encircles an area of unsuitable habitat

Background Extinction

The ongoing extinction of individual species due to environmental or ecological factors such as climate change, disease, loss of habitat, or competitive disadvantage in relation to other species

Mass Extinction

When a large number of species go extinct over a short period of time due to major events (tend to be followed by rapid diversification and adaptive radiation)

Adaptive Radiation

Evolution of many species when introduced to new environmental challenges