Evolution - Unit 7

Organisms are identified or categorized by…

the fossil record, morphology, embryological patterns of development, and chromosomes/macromolecules (DNA)

Morphology

branch of biology that deals with the form of living organisms, and with relationships between their structures

The closer organisms are on a tree of life…

the more recent they have a common ancestor

Cladistics

classification that involves ancestral and derived characters to establish relationships

Ancestral characters

traits that evolved early and have been passed down through inheritence/generations

Derived characters

big groups of organisms divided into smaller groups

The primary assumption of cladograms is…

the more shared derived characters organisms share, the more recent they evolved from a common ancestor; this is incorrect as shared derived characteristics could have evolved from similar selective pressures not a common ancestor

Morphological characters

physical traits (underlying structure) of an organism to determine if organisms are related or not; homologous traits apply but analogous traits do not apply

Phylogenetic species concept

using DNA to determine relationship between organisms (EX: species that look alike but have different DNA are different species)

Typological species concept

the more two or more organisms look alike, the more they are related (not true)

Biological species concept

members of species can interbreed but produce fertile offsrping

Taxonomy

Naming and grouping organisms according to their characteristics and evolutionary history, often using morphology to classify them

Biochemical Characters

Protein and DNA sequences between species to determine amount of relatedness

Molecular Clocks

Darwins four principles of NS are…

1) individuals in a population are geneticlly different

2) variations can be inherited

3) malthusian theory

4) fitness (variations give organisms increased reproductive sucess

Descent with modification

all present life descended from previous life forms

The fossil record is based on…

the law of superposition, succession of forms, and the principle of fossil succession

Law of superposition

the oldest fossils/rocks are found at the bottom while newer/younger ones are found near the top

Succession of forms

structures in earlier fossils (towards the top) are more detailed and complex while structures of older fossils are more simple, showing organisms show up in a predictable chronological order

Principle of fossil succession

fossils are found in a specific and determinable order allowing time periods to be recognized by fossils in that layer

Intermediate species

species that have traits that are a mix of ancestral and more recent forms proving there are gaps between very different groups of organisms (EX: Tikttalik)

Homologous structures

structures on different organisms that have a common ancestor but different functions

Analogus structures

structures on different organisms that have different ancestors but similar functions

Vestigial structures

structures that have been reduce or no longer have a use (EX: tailbones, fingernails wisdom teeth)

Similarities in embryology can reveal…

that there are similarities between organisms, for example, all chordates have pharyngeal arches and tails when they are embryos but later distinguish into different functions or structures

The more similarities in macromolecules…

the more closely related the species are, confirming evolutionary history

Biogeography

the study of how organisms are distributed across the globe and how they came to be there

Imperfections of adaptations

adaptations are sometimes flawed in the organisms environment, this can also show how evolution works in an environment and sometimes can make unperfect organisms (EX: whales)

Gene pool

all the genes available to a particular population

Idealized population based off Hardy-Weinberg principle

1) no mutations (not possible in nature)

2) no movement in or out of the gene pool

3) population is large so probability applies while chance has no effect

4) mating is random

5) all alleles viable meaning all organisms reproduce (not possible in nature)

Genetic drift

a random change in the frequency of alleles (versions of alleles) purely do to chance (affects smaller populations > bigger ones)

Founder effect

A small population that branches off from another larger population may have different allele frequencies purely by chance

Population bottleneck

different alleles frequency in a population that is drastically reduced in numbers due to chance (natural disasters, etc.)

Gene flow

movement in and out of the genepool of a population

Non random mating

can lead to interbreeding

Polymorphism

many different forms of the same species living in one population which helps species live under different selective pressures

Stabilizing selection

Favors the average and selects against extreme phenotypes (both large and small), leading to reduced variation

Directional selection

Favors only one extreme (high or low) meaning the graph will be skewed to one side

Disruptive selection

Favors both extremes while the average is selected against

Frequency dependant

the frequency of the most common phenotype will decrease while the less common will increase (EX: predator/prey)

Premating (prezygotic) isolating mechanisms

occurs before the zygote is formed (EX: mating rituals)

Postmating (postzygotic) isolating mechaisms)

occurs after the zygote is formed (EX: the organism may be infertile due to organisms mating despite contradictions

Allopatric

organisms speciate due to being geographically isolated and different selective pressures

Sympatric

occurs without isolation and orgaisms often speciate due to changes in chromosomal content

Ring species

organisms that mate with neighboring organisms causing little changes that end up becoming a significant change causing the inability to interbreed

Adaptive Radiation

diversification of a organism that shares a single common ancestor (one common ancestor speciates) (EX: galapogos birds)

Coevolution

Organisms (predator/prey or paratism) influence each others evolution (EX: as seeds become thicker the birds beaks will become thicker)

Convergent evolution

organisms under similar selective pressures become similar even if they do not share a common ancestor (analogous structures)

Divergent evolution

similar species become dissimilar due to different selective pressures

Gradual rate of evoultion

evolution occurs over a long period of time due to slow changes in selective pressures

Punctuated equilibrium

rapid evolution due to rapidly changing selective pressures which is often followed by long periods of stability