AP Biology Unit 7

Ch 1: Intro to Natural Selection

EQ: How fast is the process of evolution?

Evolution is genetically considered to be a very slow process… over 1,000s or millions of years!

But can evolution happen quickly?

Studies are suggesting evolution can happen quicker than we realized… this is called microevolution

Contemporary microevolution is ongoing genetic changes in a population.

Ch 2:

EQ: What are the origins of theory of evolution?

Charles Darwin

In 1859, Darwin published On the Origin of Species, which focused biologists’ attention on the great diversity of organisms

What is evolution?

• Darwin proposed “descent with modification” i.e. current species are descendants of ancestral species

• today, we define evolution as the change in genetic makeup of a population over time due to natural selection

Conditions necessary for natural selection…

1) variation exists in a population- organisms w/ favorite phenotypes have improved chance of survival

2) competition- organisms in. a population compete w each other for limited resources (food, sexual partners, space/territory, nutrients, light for plants)

Adaptations- traits/behaviors that provide an advantage in a particular environment

fitness- ability of an organism to survive and produce fertile offspring

reproductive success- the production on of offspring (applies to individuals)- “winners” of evolution!

heritability- the ability to pass on adaptations to new generations

natural selection- are the traits of individuals w more reproductive success become more common in the population

what changed?…

• rise of paleontology in the 17000s study of remains of past organisms (fossils) ,found in sedimentary rock layers (strata)

  • fossils were different compared to modern forms

  • boundary between strata represented catastrophic event that destroyed many species; new species replaced them

  • extinctions were common

other relation new proposals…

• geologists James Hutton (1726-1797) and Charles Lyell (1797-1875) suggested that geological changes were very slow gradual processes… in other words, Earth is really old!

Jean-Baptiste de Lamarck (1744-1829)

Unit 7-Ch 3:

EQ: How does natural selection differ from artificial selection?

Natural selection- overtime, increase in frequency of individuals w favorite adaptations results in organisms becoming well suited for life in their environment (“fittest”)

Key features of natural selection…

1) individuals w favorite traits survive and reproduce at a higher rate than other individuals… resulting in increased frequency of these adaptations in given environment

2) when the environment changes, natural selection may result in adaptation to new conditions, sometimes giving rise to new species

3) populations, not individuals, evolve over time ***

4) natural selection can only increase or decrease heritable traits that differ among individuals in a population (only mutations create new differences)

5) the specific traits that are adaptive will vary from place to place and over time

artificial selection- humans modify other species over generations through selective breeding of individuals w desired traits

Unit 7- ch 4:

EQ: who were Hardy and Weinberg?

Factors of evolution:

• pinky: shrink/small population

• ring: nonrandom mating

• middle: mutation

• pointer: movement/gene flow

• thumb: natural selection

Godfrey Hardy and Wilhelm Weinberg:

Hardy-Weinberg principle states that genetic variation in population remains constant from one generation to the next in the absence of disturbing factors

populations- group of individuals that live in the same area and inter breed, producing fertile offspring

gene pool- consists of all the alleles in population

allele frequency- how common an allele is in a population (usually expressed as a decimal/percentage)

Hardy-Weinberg equation: p2+2pq+q2= 1(decimal) (100%- percentage)

• used to test whether population is evolving

genetic variation required for population to evolve, but does not guarantee that it will

allele frequency= p or q values

p+q=1

p- dominant allele

q- recessive allele

p2- homozygous dominant (AA)

2pq- heterozygous dominant (Aa)

p2- homozygous recessive (aa)

individuals/people/organisms/phenotypes= p2, q2, 2pq

***Hardy-Weinberg equation describes genetic makeup expected for population is not evolving at specific locus under the following conditions

• large/growing pop

• random mating

• no natural selection

• no movement/gene flow

• no mutation

no genetic evolution= Hardy-Weinberg Equilibrium

Hardy-Weinberg Equilibrium p2+2pq+q2=1

• need at least 2 generations to compare in order to determine equilibrium

Unit 7: Ch 5-

EQ: What are gene flow and genetic drift, and how do they relate to natural selection?

Gene flow (“pointer finger”)

• movement of alleles among populations… alleles are transferred through movement of fertile individuals or gametes

• high rates of gene flow can reduce genetic variation over time (diluted gene pool) OR improve adaptation to local conditions

Genetic drift (sudden change)

• process where allele frequencies decrease suddenly from one generation to the next*

• reduces genetic variation through loss of alleles, especially in small populations

• the smaller a sample, the more likely that chance alone will cause deviation from a predicted result

Genetic Drift can lead to…

Founder effect occurs when a few individuals become isolated from a larger population

• allele frequencies suddenly change… due to chance

Genetic Drift can be caused by:

• Bottleneck effect can result from a drastic reduction in population size due to a sudden environmental change

• if the population remains small, it may be further affected by genetic drift

** Summary of Effects of Genetic Drift

1) significant in small populations

2) can cause allele frequencies to change at random

3) lead to a loss of genetic variation within populations

4) cause harmful alleles to become fixed

gene flow and genetic drift both lead to natural selection

3 modes of natural selection (“thumb”)

1) directional selection occurs when conditions favor individuals at one end of the phenotypic range

2) disruptive selection occurs when conditions favor individuals at both extremes of the phenotypic range

3) stabilizing selection occurs when conditions favor intermediate variants and act against extreme phenotypes

Balancing selection- occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population

• balancing selection could include:

  • heterozygous advantage (heterozygous have higher fitness)

  • frequency-dependent selection (fitness depends on frequency)

Why can’t natural selection produce perfect organisms?

1) selection can act only on existing variations

2) evolution is limited by historical constraints

3) adaptations are often compromises

4) chance, natural selection, and the environment

Unit 7: Ch 6-

EQ: what is the evidence for evolution? And what is Phylogeny?

4 types of evidence for evolution

1) direct observations

2) homology

3) biogeography

4) fossil record

1) direct observations

• biologists have observed evolutionary change in thousands of studies, for example:

  • rock pocket mouse- fur color

  • Sticklebacks- pelvic spines

  • MRSA- antibiotic resistance

2) homology

• similarity of structures resulting from common ancestry

• Related species can have characteristics with underlying similarity that function differently

3) anatomical homologies

• homologous structures are anatomical similarities that represent variations on a structural theme present in a common ancestor

• Comparative embryology reveals anatomical homologies not visible in adult organisms

• Vestigial structures are remnants of features that served important functions in an organism’s ancestors but serve no current purpose

• Analogous traits arise when species independently adapt to similar environments in different locations, and can lead to convergent evolution, or the evolution of analogous features in distantly related groups

Molecular homologies (determine relatedness of DNA’s sequence)

• similar genes, amino acids, proteins and other structures inherited from common ancestor

• More similarities= more closely related

3) biogeography

• scientific study of the geographic distribution of species

  • islands generally have many endemic species (found nowhere else in the world)… often closely related to species on the nearest mainland or neighboring island

4) fossil record

• provides evidence that species have changes through time and many species have gone extinct and can reveal origins of new groups of organisms

*Intro to Taxonomy

Phylogeny- the evolutionary history of a species or groups of related species

Modern phylogeny

• phylogeny is inferred from similarities in morphology, genetics and biochemistry

  • common ancestry will reflect evolutionary relationships (similarities likely to be more closely related)

• Relationships are shown with general cladogram, or more specifically a phylogenetic tree

unit 7: ch 7:

EQ: how does phylogeny relate to cladistics?

Phylogenetic trees- branch lengths

• can reflect the number of genetic changes in DNA sequence

• Can represent chronological time determined from fossil record

Cladistics: classifying organisms by common descent

• a clade is a monophyletic group (ancestor species and all descendants)

Paraphyletic group

• include an ancestral species and some, but not all descendants

Polyphyletic group

• include distinctly related species, but not their most recent common ancestor

Shared ancestral vs derived characters

• a shared ancestral character is a trait that originated in an ancestor of a clade

• A shared derived character is a new trait (or loss of a trait) unique to a particular group

Ingroup vs out group

• An ingroup is the group of species being studied

• An outgroup is a species or group of species closely related to but not part of the ingroup

Using characters to create a cladogram

Unit 7: Ch 8-

EQ: How does natural selection lead to new species, or elimination of species

FRQ= measure overall fitness of evolution is reproductive success

Natural selection: a closer look

• natural selection results in adaptive radiation… over a very long time this can lead to the formation of a new species

speciation

• process by which 1 species splits into 2 or more species through reproductive isolation

microevolution vs macroevolution

• speciation creates conceptual bridge between microevolution (changes in allele frequency) and macroevolution (broad patterns of evolutionary change); also punctuated equilibrium suggests rapid episodes of speciation between long periods of little/no change

the term “species” includes morphology and physiology, biochemistry, and dna sequences

species= group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring

limitations of the species concept:

1) cannot be applied to fossisl or asexual organisms

2) emphasizes besence of gene flow between speices, but gene flow does sometimes occur between distinct species

Allopathic Speciation (geo barrier)

• geographic barrier exists to prevent breeding and the barrier delends on the ability of a population to disperse

  • for example, canyon create barrier for small rodents but not birds, coyotes or trees pollen

Sympathies speciation (no geo)

• occurs in populations living in same geographic area, but gene flow is reduced through other factors including:

  • polyploidy (extra sets of chromosomes and common in plants)

  • Habitat differentiation

  • Sexual selection

Mass extinction- disruptive changes to the global environment cause the rate of extinction to increase drastically, where large numbers of species become extinct worldwide

Current estimates suggest that 99% of all living organisms that have ever lived on Earth are now extinct

Extinction

Organisms cannot adapt quickly enough to rapid environmental changes like:

• invasive species

• Diseases

• Natural disasters

• New predators

• Humans

Unit 7- Ch 9

EQ: what are the origins of life?

the first cells

• earth formed 4.6 billion years ago

• Oldest fossils are prokaryotes from ~3.5 billion yrs ago

  • single celled organisms in bacteria and archaea domains

Conditions of early Earth

• early atmosphere had little oxygen, likely only water vapor and compounds released by volcanic eruptions. Water vapor condensed into oceans, and hydrogen escaped into space

Phase 1: abiotic synthesis

Atmospheric components were converted into monomers through variety of processes requiring some sort of catalyst

Miller-Urey experiment

In 1953, Stanley miller and Harold Urey showed experimentally that abiotic synthesis of organic molecules was possible in a reducing atmosphere

Phase 2: synthesis of macromolecules

• next, small organic molecules polymerized to form larger molecules… monomers are known to bind to mineral particles, holding them in close proximity and allowing bonds to form

Phase 3: development of pre-cells (protocells)

Development of membrane by phospholipid molecules, which naturally arrange themselves into spherical shapes

Phase 4: formation of self-replicating molecules

• first, genetic material was likely rna

• Riboenzymes are rna molecules that can catalyze reatxtions

RNA world

• copying errors (mutations) occasionally result in daughter molecules w improved replication… faster, more accurate self-replication would leave more descendant molecules resulting in an “rna world”