1309 Unit 1 Exam Review

Evolution

• Evolution is genetic change in a population over time 

• Occurs when allele frequencies change across generations 

• Evolution happens in populations, not individuals 

Gene pool

all alleles present in a population

Allele frequency

• proportion of a specific allele in the population 

• Evolution can be detected by: 

  • Comparing allele frequencies between populations 

  • Observing changes in allele frequencies over time

Natural Selection

1. Struggle for existence: Individuals compete for the limited resources that enable them to survive.

2. Unequal reproductive success (natural selection): The inherited characteristics of some individuals make them more likely to obtain resources, survive, and reproduce.

3. Descent with modification: Over many generations, a population’s characteristics can change by natural selection, even giving rise to new species.

Fitness

ability to survive and reproduce successfully

Adaptation

heritable trait that increases fitness in a specific environment

Directional selection 

• Favors one extreme phenotype 

• Example: Under normal conditions, finches with average beak size are favored, but during drought finches with larger beaks that could open tough seeds were favored

Stabilizing selection

• Favors intermediate (average) phenotype 

• Example: average birth weight in humans

Disruptive selection

• Favors both extreme phenotypes 

• Example: very light and very dark snails survive better than intermediate ones

Sexual Selection

A form of natural selection based on mating success. Results in nonrandom mating, which can lead to evolution

Intrasexual selection

competition within the same sex (e.g., males competing)

Intersexual selection

mate choice (e.g., females choosing mates with certain traits)

nonrandom mating

can lead to evolution

Mutation

• Random changes in DNA sequence 

• Source of new genetic variation 

• Can be harmful, neutral, or beneficial

Genetic Drift

• Random changes in allele frequencies 

• Strongest in small populations

Bottleneck effect

 population drastically reduced → loss of genetic diversity

Founder effect

small group starts a new population with limited variation

Gene Flow

• Movement of alleles between populations 

• Caused by migration 

• Reduces genetic differences between populations

Hardy-Weinberg Equilibrium

A model describing a population that is not evolving.

Conditions (must all be met):

• No mutation 

• No migration 

• No genetic drift

• Random mating 

• No natural selection

Fossil Evidence

• Fossils provide evidence of organisms that lived in the past 

• Show gradual change over time 

• Support the idea of common ancestry 

• Limitations: 

  • Incomplete record 

  • Soft-bodied organisms rarely fossilize

Biogeography

• Study of the geographic distribution of species 

• Patterns explained by evolution and plate tectonics 

• Example: 

  • Australia’s isolation led to dominance of marsupials

Homologous structures

• Similar structures with different functions 

• Indicate common ancestry

Vestigial structures

• Reduced or nonfunctional structures 

• Remnants of ancestral traits

Embryology

• Study of early development 

• Similarities among embryos suggest shared ancestry

Molecular Evidence

• DNA and protein similarities across species 

• All life shares: 

  • DNA as genetic material 

  • Similar genetic code 

  • Similar processes of gene expression

Microevolution

• small-scale changes within populations (short term) 

Macroevolution

• large-scale changes leading to new species (long term) 

Species

• a group of organisms that can interbreed and produce fertile offspring 

• Limitations: 

  • Does not apply to fossils or asexual organisms

Reproductive Isolation

• If the potential to interbreed defines species, reproductive isolation results in new species.

• cannot mate and produce offspring in nature

• can mate but offspring is sterile

habitat isolation

different environments

temporal isolation

active or fertile at different times

behavioral isolation

different courtship activities

mechanical isolation

mating organs or pollinators incompatible

gametic isolation

gametes cannot unite

Prezygotic Barriers

before fertilization (ex. habitat, temporal, behavioral, mechanical, gametic)

Postzygotic Barriers

after fertilization (ex. hybrid inviability, hybrid infertility, hybrid breakdown)

Allopatric Speciation

• Physical barrier separates populations 

• Most common form

Parapatric speciation

• Formation of new species when part of a population enters a habitat bordering the parent species’ range, and the two groups become reproductively isolated

• Limited gene flow

Sympatric speciation

• Occurs within the same geographic area 

• Although the habitat may appear uniform, often it consists of many microenvironments that select for different phenotypes

Background extinction

Normal rate of species loss

Mass extinction

• Rapid, large-scale extinction events 

• Five major events in Earth’s history 

• Current evidence suggests a sixth mass extinction due to human activity

Mass extinction causes

• Habitat destruction 

• Pollution 

• Invasive species 

• Overexploitation

Taxonomy

• Science of naming and classifying organisms 

• hierarchy

  • Domain, kingdom, phylum, class, order, family, genus, species

Phylogeny

Study of evolutionary relationships

Cladograms

Diagrams showing evolutionary relationships

Clade

group consisting of a common ancestor and all descendants

Shared derived traits

traits unique to a group

Monophyletic

includes ancestor and all descendants

Paraphyletic

missing some descendants

Polyphyletic

excludes common ancestor

Earth formed

~4.6 billion years ago

Life appeared

~4 billion years ago

Early Earth conditions

• High temperature and pressure 

• No oxygen 

• Harsh, unstable environment

Chemical Evolution

• Simple inorganic molecules formed organic molecules 

• Occurred in a “chemical soup” environment

Miller Experiment

• Simulated early Earth conditions 

• Produced organic molecules from inorganic substances 

• Demonstrated that building blocks of life could form naturally

RNA World Hypothesis

• RNA was likely the first self-replicating molecule 

• Capable of: 

  • Storing genetic information 

  • Catalyzing chemical reactions

Protocells

• Early cell-like structures 

• Formed when lipids created membranes 

• Enclosed RNA and other molecules 

Early Life

• First organisms were prokaryotes 

• Appeared ~3.5 billion years ago 

• Lived in anaerobic environments (no oxygen) 

Photosynthesis and Oxygen

• Photosynthesis evolved in early bacteria 

• Led to increase in atmospheric oxygen 

• Caused major environmental changes

Endosymbiosis Theory (Origin of Eukaryotes)

Mitochondria and chloroplasts originated from free-living bacteria

Evidence:

• Own DNA 

• Own ribosomes 

• Similar to bacteria in size and structure

Multicellularity

• Evolved ~1.2 billion years ago 

• Allowed specialization of cells 

• Led to increased organism complexity

Paleozoic Era

spans 543–248 mya

• Cambrian

  • Cambrian explosion (rapid diversification) 

• Ordovician

  • First land plants and vertebrates 

• Silurian

• Devonian – “age of fishes”

• Carboniferous – “age of amphibians”

  • Carboniferous swamps included ferns and early seed plants, some towering 40 m. 

  • By end of the period, many of the plants had died, buried beneath the swamps to form coal 

• Permian

  • ended with the largest mass extinction in the history of the Earth

  • Global climate altered drastically due to accumulation of CO2, rising temperatures, and depletion of O2.

Cambrian

Cambrian explosion (rapid diversification)

Ordovician

First land plants and vertebrates

Silurian

paleozoic era

Devonian

“age of fishes”

Carboniferous

• “age of amphibians”

  • Carboniferous swamps included ferns and early seed plants, some towering 40 m. 

  • By end of the period, many of the plants had died, buried beneath the swamps to form coal

Permian

• ended with the largest mass extinction in the history of the Earth

• Global climate altered drastically due to accumulation of CO2, rising temperatures, and depletion of O2.

Mesozoic Era

“Age of reptiles” spans 248-65 MYA

• Dinosaurs dominate 

• Ends with asteroid impact 

Triassic

period

Jurassic

period

Cretaceous

period

Cenozoic Era

spans 65 MYA - present

• “Age of mammals” 

• Mammals diversify 

• Humans appear

Primates

• Traits: 

  • Opposable thumbs 

  • Long arms

  • Binocular vision 

  • Large brains 

  • Upright locomotion

• Divided into 3 main lineages

  • Prosimians

  • Monkeys

  • Hominoids (apes)

Hominins (Human Lineage)

• Distinguished by: 

  • Bipedalism 

    • Numerous skeletal adaptations in fossils and living species tell us the form of locomotion used

      • Shorter arms, longer legs

      • Fixed, non-opposable big toe

      • More centered foramen magnum (hole in skull where spinal cord leaves brain)

      • Larger brain size

Australopithecus group

Early bipedal hominins

Homo habilis group

Tool use

Homo erectus

First to leave Africa

Homo sapiens

Modern humans

Key Human Traits

• Complex language 

• Culture 

• Advanced cognition

Struggle for existence

Individuals compete for the limited resources that enable them to survive.

Unequal reproductive success (natural selection)

The inherited characteristics of some individuals make them more likely to obtain resources, survive, and reproduce.

Descent with modification

Over many generations, a population’s characteristics can change by natural selection, even giving rise to new species.

Polyploidy

cell with extra chromosome sets

hybrid inviability

embryo dies before reached reproductive maturity

hybrid infertility

offspring is born sterile

hybrid breakdown

can reproduce (fertile), but its offspring may have abnormalities that reduce its fitness

allele

one of two or more alternative forms of a gene

heterozygous

possessing two different alleles for a particular gene

homozygous

possessing identical alleles of one gene