Evolution

Root

the base of the phylogenetic tree

Node

point of MRCA on phylogenetic tree

Clade

group of organisms containing MRCA and ALL descendants

Sister Taxa

organisms most closely related

Outgroup

the first full break off on phylogeny

Why are phylogenetic trees best described as hypotheses?

relationships are inferred and are not 100% factual (no way to truly tell)

What are the 4 main requirements for life?

- must work to avoid decay and disorder

- has to create a closed system (be made of cells)

- have some molecule that can carry information

- information must evolve by natural selection

What is our current understanding of the relationships among the domains of living organisms?

2-domain - all multicellular organisms descended from archaea and all others from bacteria

What is the key distinction between the 3-domain model and the 2-domain model?

the 2-domain model shows that eukaryotes developed out of archea

What is LUCA and why was it not the first living organism?

LUCA - last universal common ancestor

the origin of life was a much smaller unicellular organism that came billions of years before LUCA

What are some shared characteristics between human cells and LUCA?

1. genetic code stored in DNA

2. enzymes for DNA replication and repair

3. proteins produced through an RNA intermediate and translated by ribosomes

4. uses hydrogen gradients to generate ATP

5. lipid bilayer membrane with ions pumps

What is the general process responsible for the diversification of life on Earth?

adaptation

How did new ideas about geology influence Darwin's ideas of evolution by natural selection?

- as fossils were studied, it was found that profound change could take place through cumulative effect of slow, continuous processes

- if this can happen geologically, why can't it happen biologically?

What is adaptation?

an inherited characteristic of an organism that enhances their survival and reproduction in certain environments

What is natural selection?

the process where organisms adapted to their environment tend to survive and produce more offspring (descent with modification) leading to change in allele frequencies over time

What are the 3 requirements for natural selection to occur?

1. variation

2. heritability

3. differential reproductive success

What is the major outcome of natural selection in a population?

accumulation of favorable traits in a population and decreasing genetic variation

Particulate Inheritance

hereditary determinants maintain their integrity from generation to generation

Blending Inheritance

traits of offspring are achieved by blending traits of parents

Why is particulate inheritance necessary for the process of natural selection?

particulate inheritance preserves the variation necessary for natural selection to occur; blending inheritance leads to "average" over time

Trait

one of two or more detectable variants in a genetic character

Allele

any of the alternative versions of a gene that may produce distinguishable phenotypic effects

Dominant Allele

an allele that is fully expressed in the phenotype of a heterozygote

Recessive Allele

an allele whose phenotypic effect is not observed in a heterozygote

Homozygote

having two identical alleles for a given gene

Heterozygote

having two different alleles for a given gene

Genotype

the genetic makeup, or set of alleles, of an organism

Phenotype

the observable physical traits of an organism

Why is mutation the "raw material of evolution"?

mutations change nucleotides in the sequence of an organisms' DNA generating new alleles

Relative Fitness

the contribution an individual makes to the gene pool of the next generation, relative to the contributions of the other individuals in the population

Positive Mutation

helps organism

Negative Mutation

harms organism

Neutral Mutation

no effect on organism

Why is mutation "random" and how does this affect evolution?

cannot predict when a mutation will occur, makes evolution unpredictable (don't occur out of necessity)

How do meiosis and sexual reproduction contribute to variation in a population?

Meiosis:

- independent assortment

- crossing over

- random fertilization

Sexual Reproduction:

- combination of genetic material

- mutation

- diversity in offspring

Independent Assortment

each pair of alleles separates independently of each other pair during gamete formation

Crossing Over

the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring

Random Fertilization

any sperm can fertilize any egg

Combination of Genetic Material

each parent contributes a unique set of genetic material

Mutation

random changes in DNA sequence

Diversity in Offspring

offspring inheriting combination genes that is different from both parents

What conditions would asexual reproduction be favored in?

when an organism has a beneficial mutation

What conditions would sexual reproduction be favored in?

when a population experiences new environmental conditions (where genetic variation is favorable)

Population

group of individuals of the same species that live in the same area, interbreed, and produce fertile offspring

Genetic Locus

a specific place along the length of a chromosome where a given gene is located

Gene Pool

the aggregate of all copies of every type of allele at all loci in every individual in a population

Fixed Allele

if only one allele exists for a particular locus in a population

Allele Frequency

the proportion of alleles in a population

What are the 5 conditions for Hardy-Weinberg equilibrium?

1. no mutations

2. random mating

3. no natural selection

4. extremely large population size

5. no gene flow

Population Bottleneck

a sudden change in environment that drastically reduces the size of a population

Founder Effect

when a few individuals become isolated from a larger population and this smaller group establishes a new population with a different gene pool

What does it mean for a population to be in Hardy-Weinberg equilibrium?

allele and genotype frequencies do not change over time

How can deviation from HWE be used to detect evolution at a genetic locus?

analzye genotype frequencies and compare them to the expected values under HWE

What will the change in allele frequency look like in a selective environment?

when selection is occurring, HWE is not occurring; the favorable allele will increase in frequency and non favorable will decrease

Genetic Drift

chance events that cause allele frequencies to fluctuate unpredictably from one generation to the next

What is the effect of genetic drift on allele frequencies in a small population?

changes allele frequencies more randomly and dramatically (fixation or loss); drift DOMINATES and forces selection

Why is it advantageous to maintain genetic variation in a population?

- without variation, it is way easier to get to extinction

- low genetic variation can leave a population vulnerable

- allows future generations to adapt to changing environments

- selection cannot occur without variation

Directional Selection

conditions favor individuals at one extreme of a phenotypic range

Disruptive Selection

conditions favor individuals at both extremes of a phenotypic range

Stabilizing Selection

both extreme phenotypes are selected against

Balancing Selection

when multiple alleles are maintained in a population

Heterozygote Advantage

if individuals who are heterozygous at a particular locus have greater fitness than do both kinds of homozygotes

Frequency-Dependent Selection

a situation where fitness is dependent upon the frequency of a phenotype or genotype in a population

Gene Flow

the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes

How does gene flow increase/decrease the fitness of a population depending on the context?

gene flow homogenizes allele frequencies (low frequency alleles benefit; high frequency alleles do not)

What distinguishes gene flow and genetic drift?

gene flow (increase variation) is migration and genetic drift (decrease variation) is chance events (in small populations)

Why is natural selection fundamentally different from genetic drift and gene flow?

genetic drift does not depend on an allele's beneficial or harmful effects (selection is predictively adaptive)

Microevolution

changes over time in allele frequencies in a population

Macroevolution

the broad pattern of evolution above the species level

Species (Biological Species Concept)

a group of individuals who interbreed in nature and produce viable, fertile offspring

What are the limitations of the biological species concept?

- the number of species this concept can be applied to is small

- species are designated by the absence of gene flow

- can't be applied to all cases (asexual reproducing organisms, fossils)

What is the relationship between biodiversity, speciation, and extinction?

speciation happens as a result of diversity and extinction is the loss of species (speciation -> diversity -> extinction)

Pre-Zygotic Reproductive Barrier

block fertilization from occurring

Post-Zygotic Barrier

contribute to the reproductive isolation after a hybrid zygote is formed

What are the steps of speciation?

1. barrier to gene flow

2. mutation/drift/selection

3. genetic divergence

4. reproductive isolation

Allopatric Speciation

gene flow is interrupted when a population is divided into geographically isolated subpopulation

Sympatric Speciation

speciation occurs in populations that live in the same geographic area

Adaptive Radiation

rapid diversification and adaptation to new ecological roles (speciation on steroids)

Conditions for Adaptive Radiation

- lack of competition

- extrinsic factors (formation of new island or lake, extinction event)

- intrinsic factors (innovations that allow species to exploit new resources that promote diversification)

Effects of Mass Extinction on Biodiversity

- decrease diversity

- comes back in new forms

Evo-Devo

(evolutionary developmental biology) the attempt to understand the evolution of form

What was the initial major discover of evo-devo?

the discovery that genes in fruit flies had counterparts in all animals

How can a small genetic change in a regulatory gene lead to large structural changes in an organism?

the activation or inhibition of a gene can cause major structural effects (ex. mosquito with legs on head)

hox genes regulate the expression of all other genes (affects regulatory genes)

What does it mean to say evolution is a "tinkerer"?

teaching old genes new tricks

What implications does evolution being a "tinkerer" have on how new structures evolve?

new structures evolve as a result of older structures

What is the role of microevolutionary processes in macroevolutionary processes?

gene regulatory networks and microevolution can explain evolution of novel structures that lead to macroevolution