Biology 5C Final

Evolution

A change in allele frequency in a population over time

Mechanisms for Evolution

Natural selection, genetic drift, gene flow

Genetic Drift

The random change of allele frequencies from one generation to the next due to random sampling

Population Size

The number of organisms in a population

How Genetic Drift Causes Evolution

Genetic drift makes evolution more random and reduces genetic variation

The Effects of Population Size on Genetic Drift

Drift causes more extreme changes in smaller populations

Founder Effect

The acceleration of genetic drift when a small number of individuals become isolated from a larger population

Bottleneck Effect

A magnification of the effect of genetic drift due to a reduction of size within population

Gene Flow

The movement of alleles between populations due to migration, tends to make populations more genetically similar over time

The Effects of Gene Flow on Allele Frequency Differences Between Populations

Genetic swamping, adaptive introgression

Genetic swamping

The reduction in a population’s ability to adapt due to gene flow from maladaptive populations

Adaptive Introgression

The movement of beneficial (adaptive) alleles between populations, which facilitates adaption

Natural Selection

The differential survival and reproduction of individuals or genotypes due to differences in phenotype

Selection for

A trait causes both it and underlying allele to increase frequency

Selection against

A trait causes both it and underlying allele to decrease frequency

Fitness

A quantitative measure of how much an individual with a particular phenotype or genotype will contribute to the next generation

How does Fitness relate to Natural Selection

Natural selection favors organisms that can survive and reproduce

3 General forms of Selection

Directional, disruptive, stabilizing

Directional Selection

Natural selection that causes trait distribution to shift in one direction (increase or decrease)

Disruptive Selection

Natural selection in which individuals on both extremes survive and reproduce more than individuals in the middle (selection for extremes, selection against intermediate)

Stabilizing Selection

Natural selection in which intermediate phenotypes survive and reproduce more than the extreme phenotypes (selection for intermediate, selection against extremes)

Sexual Selection

A process in which individuals with certain inherited characteristics are more likely to obtain mates than other of the same sex

Sexual Dimorphism

Differences in phenotype between sexes in animals

Balancing Selection

Natural selection that maintains more than one phenotypic form or allele, maintain variation rather than reduces it

Speciation

An evolutionary process in which one species split into two more more species

Microevolution

Evolutionary change below species level

Macroevolution

Evolutionary change above species level

Species

The basic unit of classification and taxonomic rank of organisms

Biological Species Concept

Definition of species in which a group of populations whose members have the potential to interbreed, produce offspring, and does not interbreed with other species

Reproductive Isolation

When biological barriers impede members of two different species from interbreeding and producing offspring

Prezygotic Barriers

Block fertilization from occurring by impeding different species from attempting to mate

Habitat Isolation

Two species that occupy different habitats within the same area rarely encounter each other

Temporal Isolation

species that breed at different times cannot mate

Behavioral Isolation

Courtship rituals and other behaviors unique to a species

Pollinator Isolation

Species of a plant attract different types of pollinators

Mechanical Isolation

Mating is attempted, but morphological differences prevent its successful completion

Gamete Isolation

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

Zygote

The diploid cell produced by the union of haploid gametes during fertilization (fertilized egg)

Postzygotic Barriers

Prevent hybrid zygotes from developing into viable, fertile adults

Postzygotic Barriers occur by

Reduced hybrid viability, reduced hybrid fertility, hybrid breakdwon

Reduced hybrid viability

Genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment

Reduced hybrid fertility

If an organisms’s parents differ in chromosomes number or structure, meiosis can fail and lead to sterility in offspring

Hybrid Breakdown

First generation hybrids are viable and fertile, but second generation offspring are sterile or unhealthy

Reductive Isolation Occurs Along a Continuum

Species can be mostly distinct, but still exchange genes at low levels

Morphological Species Concept

Definition of a species in terms of measurable subjective criteria (structural features)

Ecological Species Concept

Definition of species in terms of ecological niche, the sum of its interactions with living and nonliving parts of the environment

Allopatric Speciation

Populations are genetically isolated

Sympatric Speciation

Populations are mixed, not genetically isolated

The Process of Allopatric Speciation

The gene pools of isolated populations may diverge genetically through mutation, natural selection, genetic drift

Separation can result from

Vicariance, dispersal

Vicariance

division of an existing population by a barrier

The Process of Sympatric Speciation

Speciation occurs in populations that live in the same geographic area and requires gene flow that is reduced by drivers

Drivers of Sympatric Speciation

Polyploidy, sexual selection, hybrid differentiation

Polyploidy

Mutations causes whole genome duplications and form a new species within a single generation without geographic separation

Autopolyploids

An individual that has more than two chromosomes derived from a single species

Allopolyploids

A fertile individual that has more than two chromosomes derived from different species interbreeding and combining their chromosomes

Habitat Differentiation

Adaptation to new habitats and resource sources

Hybrid Zone

A region where members of different species mate and produce hybrid offspring

Hybrid

Result of mating between species with incomplete reproductive barriers

Possible Outcomes in a Hybrid Zone

Reinforcement, fusion, stability, hybrid speciation

Reinforcement

If hybrids are less fit than the parent species, then natural selection strengthens prezygotic barriers to reproduction and reduces the changes of hybrid formation

Fusion

Gene flow between species can weaken reproductive barriers and the two parents species may fuse into single species

Stability

A hybrid zone in which hybrids continue to be produces, causing the hybrid zone to be stable

Hybrid Speciation

Hybrids in a hybrid zone may become reproductive isolated from both parent types

Punctuated Equilibrium

In the fossil record, long period of apparent stasis, in which a species undergoes little to no morphological change, interrupted by brief periods of sudden change

According to the fossil record, the rate of speciation varies

Evidence from lab studies and instantaneous polyploid speciation show that speciation can be rapid

Abiotic Synthesis

The synthesis of organic molecules by physical or chemical means

Macromolecule

Large molecules, often composed of smaller subunits

Protocells

Early, simple precursors of cellular organisms

Earliest fossils of single celled life on Earth dates to

3\.5 billion years ago

Simple reactions among C, O, N, H could have been fueled by

Lightning, hydrothermal vents, volcanic eruptions

Muller-Urey Experiment (1953)

Created conditions like early earth in lab, heated water, methane, ammonia, and hydrogen and applied electrical charge, observed the formation of 11 out of the 29 essential amino acids

The Reasons RNA is Thought to be a Likely Key Player in the Origin of Life

RNA can function like an enzyme (ribosomes) and information storage molecule

RNA World Hypothesis

Hypothesis that early earth relied on mostly RNA, with DNA evolving later

Fossils

Impressions of prehistoric organisms preserved in petrified form or a mold in rock

Radiometric Dating

A method using the decay of radioactiv3e isotopes in substances as a clock to date them

The General Sequence of Events in the History of Life

Prokaryotes, atmospheric oxygen, single celled eukaryotes, multicellular eukaryotes, animals, colonization of land, humans

Prokaryotes (1.5 billion years ago)

Single celled organisms that doesn’t have nucleus or specialized organelles

Stromatolies

Structures that are formed by single celled organisms or cyanobacteria

Eukaryotes (1.8 billion years ago)

Multicellular organisms with DNA, chromosomes, nucleus

Endosymbiosis

Symbiosis in which a symbiotic organism lives inside another

Cambrian Explosion

A period of accelerated evolution of marine organisms that occurred about 530 million years ago

Possible Causes of Cambrian Explosion

Increased oxygen, increased genetic complexity of organisms, climate change

Adaptive Radiation

The rapid origin of many new species due to the adaptation to new environments (fungi, plants, arthropods, vertebrates)

Continental Drift

The movement of tectonic plates on the surface of the Earth, reconfigured landmasses

Extinction

The disappearance of species due to unfavorable changes in habitat

Mass Extinction

A large scale extinction event involving many species

The Broad Evolutionary History of Ancient and Modern Humans

Humans evolved in Africa from primate ancestors, migrated and lived alongside archaic groups, genetic diversity result of genetic drift

Aboreal

Living in trees or forests

Relative Brain Size

The size of an animal’s brain relative to its body size

Hypothesis on why the relative brain size and complexity of apes greater than other primate species

Living in complex social groups, changes in diet, environmental variability

Why linear depictions of human evolution are wrong

Humans did not evolve from modern apes, we share a common ancestor (5.5 mya)

Hominins

The clade that includes modern humans, chimpanzees, and extinct ancestral human like species

Key differences of hominins from other primates

Smaller canines, bipedalism, loss of grasping feet, tool making and use, larger relative brain size

Bipedalism

The practice of walking upright and on two feet

Knapped/flaked edge

A jagged edge on a stone tool made by striking the edge with another rock or pressure

Archaic Humans

Groups of closely related humans or human like species that live along side modern humans

Neanderthals

Group of archaic humans mostly found in Europe

Denisovan

Group of archaic humans mostly found in central Asia

The History of Intermixing Archaic Humans and evidence supporting it

Using DNA sequencing, researchers fully sequenced gnome of Neanderthals and Denisovan individuals to compare to modern human genome