Biology Exam 1

Dmitri Belyaev (1917-1985)

• How did we domesticate animals
  (e.g. dogs)?
  • Believed that genes were selected
  in the ancestors of dogs that made
  them tame
  • Could we duplicate the process by
  breeding for tameness?
  • He tested his ideas in silver foxes

  • Fur farms in russia

Farm Fox experiment

• first 2 categories - fearful/aggressive (class 1) & receptive/tolerant (class 2)

• Bred only class 2, also control population

• Minimum time around humans (make sure its genetic)

• 6th gen - dramatic changes - some foxes more dog-like (tail wagging, whimpering, licking)

• Class 3 - elite foxes → more friendly

Domestication syndrome

Suite of characteristics that accompany domestication (less musk, shorter snout, short/curly tails, spots, floppy ears)

Tameness vs domestication

Tameness - acquired trait learned during lifetime

Domestication - result of breeding for genetically=controlled traits

Darwin experiments

• pigeon breeding - artificial selection

  • Galapagos finches

Selection can occur if:

• variation is present

• Variation is heritable

• Trait influences whether reproduction occurs (/how much)

Mendelian genetics

Genes that control traits exist and can be
passed on to offspring

Lysenkoism/Lamarckianism

Characteristics that are acquired during

one’s lifetime can be passed on to offspring

Lamark inheritance of acquired traits

use & disuse of certain

characters would lead to their

enhancement or loss in a species

Lysenko inheritance

cold treatment of seeds

(vernalization) causes plants to

germinate sooner; believed their

offspring would also

Genetic evidence supports which of the following explanations for the presence of 13 different finch species on the Galápagos islands?

D. Many years ago, a small population of a single finch species migrated to the islands and evolved into the 13 species.

Artificial and natural selection differences

people instead of nature select which organisms reproduce

Natural selection

Survival and offspring production depends on heritable traits, leading to changes in traits among populations

Darwins 4 postulates of natural selection

1. Variation among individuals

2. Variation is inherited

3. More individuals are born than will survive (resources are limited)

4. Some variants survive and reproduce more than others

Analogous features share ________ function but not ________ ancestry.

similar; common

The rise of methicillin-resistant Staphylococcus aureus (MRSA) can be considered to be an example of artificial selection because

D. humans synthesize methicillin and create environments in which bacteria frequently come into contact with methicillin.

Convergent evolution

The process where unrelated species develop similar traits in response to similar environmental pressures, leading to similar adaptations.

Homologous structure

Structures in different organisms that have a similar origin but may serve different functions.

Why do we have species?

• Dividing organisms into species useful for
  understanding biodiversity and for what
  processes create new biodiversity

• A species is the fundamental unit of
  biodiversity

• Species are the conceptual bridge
  between micro & macroevolution

Microevolution

Microevolution refers to small-scale changes in the genetic makeup of a population over generations. It is driven by factors such as genetic variation, natural selection, mutation, and gene flow. These changes can lead to adaptations and the formation of new species.

Macroevolution

The process through which new species arise over long periods of time, involving significant genetic and phenotypic changes. It occurs through mechanisms like natural selection, genetic drift, and mutation. Macroevolution leads to the diversification and branching of lineages, resulting in the formation of new species and higher taxonomic groups.

Genetic drift

Random changes in allele frequencies due to chance events, leading to the loss or fixation of alleles within a population. It is more pronounced in small populations and can have significant effects on genetic diversity.

Biological species concept

• Ernst Mayr 1990

• Species = group of individuals that can interbreed in
  nature and produce fertile offspring

• They either do not interbreed, or
  They fail to produce viable, fertile offspring

How species arise under BSC

Reproductive isolation

Shortcomings of BSC

• Many distinct species can produce fertile offspring (dogs/wolves, grolar bears)

• self-reproducing bacteria

• Fossil organisms

• Fungi

Morphological species concept

different phenotype

Pro: widely applicable

Con: subjective, misidentifies polymorphic species, misses cryptic species

Phylogenetic species concept

Distinct group in a cladogram (DNA)

Pro: widely applicable, based on testable criteria

Con: relatively few well-estimated phylogenies are currently available

Ecological species concept

Distinct role in ecosystem

Unified species concept

UNIFIED SPECIES CONCEPT = apply multiple concepts and accept consensus

Central problem of species concepts

• There is a continuum of

diversity in life (from

individuals to populations, to

metapopulations, to species,

to families, etc.)

• Looking beyond evolutionary

history and combining it with

molecular, ecological,

behavioral and biological

data.

Necessities for speciation

1. interbreeding population

2. Geographic subdivision leading to 2 pops

3. evolutionary change over time

4. Formation of reproductive barriers (isolation)

Isolating barrier types

Geographic: extrinsic properties of landscape that prevent gene flow (allopatric speciation)

Reproductive: features of organisms prevent interbreeding (sympatric speciation)

Allopatric speciation

1. Vicariance - geographic barrier arises to divide one pop into 2 smaller ones

2. Dispersal (founder events) - individuals leave original pop and find a new one

Sympatric speciation

• based on behavioral differences (non-random mating), resource usage, or temporal differences

• Controversial

Mechanisms of speciation in daughter populations

Genetic drift - random changes in allele frequencies

Natural selection - daughter populations will adapt to changes

in their environment INDEPENDENT of what is occurring in the

other population (again, as long as no genes are exchanged)

Reproductive isolation types

• Prezygotic barriers

– act before fertilization

• Postzygotic barriers

– act after fertilization

Prezygotic reproductive barriers

• Premating:

  • habitat isolation (ecological)

  • temporal isolation (ecological)

  • behavioral isolation (lack of attraction)

  • Mechanical isolation (genitalia, pollination structures incompatible)

• Post-mating:

  • Gametic incompatibility (no fertilization)

  • Conspecific sperm precedence

  • Copulatory behavioral isolation

Postzygotic reproductive barriers

• reduced hybrid viability - hybrids dont survive as well

• Hybrid sterility

• Hybrid breakdown - F1 hybrids fertile, but F2 gen doesn’t develop property

Evolutionary convergence

When unrelated species independently evolve similar traits or characteristics due to similar environmental pressures.

Autoploidy

Type of polyploidy where an individual has multiple sets of chromosomes from the same species. Can occur due to errors in cell division or fusion of gametes.

A. fertile tetraploid offspring produced by self-pollination of the new species

Polyploidy

Polyploidy is a genetic condition where an organism has more than two complete sets of chromosomes. It can occur naturally or be induced artificially. Polyploidy often leads to increased genetic diversity and can result in larger, more robust organisms.

Tetraploidy

A condition where an organism has four sets of chromosomes instead of the usual two sets. It can result in increased genetic variation and can be caused by errors in cell division or hybridization.

Scala naturae

A concept in medieval and Renaissance philosophy that describes a hierarchical ladder of life forms, with humans at the top and minerals at the bottom. It suggests a fixed and unchanging order of beings, with each level being more complex and perfect than the one below it.

Robber mouse

Algerian mouse

Warfarin mouse poison

Descent with modification

"Process where species evolve over time through genetic variation, natural selection, and reproductive success. Leads to the formation of new species and adaptation to different environments."

Adaptive radiation

The process by which a single species evolves into diverse forms to exploit different ecological niches. It leads to the emergence of new species with distinct adaptations. Example: Darwin's finches in the Galapagos Islands.

Alfred Russel Wallace

Extinction rate

number of species extinct/length of time

Speciation rate

number of nodes/length of time

Necessities of adaptive radiation

• common ancestry (recent ancestors)

• Key adaptations (association between environments and morphological and physiological traits used to exploit new environment)

• Trait utility (performance/fitness advantage of trait values in environment)

• Rapid speciation (presence of 1+ emergence of new species when ecological or morphological divergence)

Phylogenies can be use to infer:

• Which CHARACTERISTICS are older or younger

• Which CHARACTERISTICS are ancestral versus derived

(better terms than ‘primitive’ versus ‘advanced’)

• Which trait evolved first

• What might the common ancestor have looked like?

• We can use methods of ancestral state reconstruction to

analyze traits one character at a time

Background extinction

he normal rate of

extinction for a taxon or biota

Mass extinction

a statistically significant

increase above background extinction rate

Main 5 extinctions

Ordovician 86%

Devonian 75%

Permian 96%

Triassic 80%

Cretaceous 76%

Causes of mass extinctions

• Physical causes

• Sea-level regressions

• Sea-level transgressions

• Ocean chemistry

• Global Climate changes

• Biological Causes

• Competition for niche

• Extraterrestrial causes

• Iridium from comets

Speciation and extinction effects on diversity

Species diversity of an

evolutionary lineage will

increase when new

member species originate

than are lost to extinction

• These changes are

influenced by plate

tectonics, mass extinctions

and adaptive radiations

Radiometric dating

Method used to determine the age of rocks or fossils by measuring the decay of radioactive isotopes.

• A “parent” isotope decays to a “daughter”

isotope at a constant rate

• Each isotope has a known half-life, the

time required for half of the parent

isotope to decay (disappear)

Principle of faunal succession

The Principle of Faunal Succession states that fossilized organisms in rock layers follow a specific order. Older layers contain fossils of simpler organisms, while younger layers have fossils of more complex organisms. This principle helps scientists determine the relative age of rock layers and establish a timeline of Earth's history.

Earth’s early atmosphere

• Nitrogen, carbon dioxide, methane and ammonia.

• Volcanoes spewed water vapor, carbon monoxide, and even

more nitrogen and carbon dioxide into the air.

• Comets also contributed water vapor, but no free oxygen.

where did the abundant oxygen that has made life as we

know it come from?

From Cyanobacteria and early photosynthetic organisms

The Miller and Urey experiments - 1953

Abiotic production of organic molecules

End of week 1: 10-15% of carbon now in

ORGANIC compounds

Later experiments: formation of sugars,

some amino acids, lipids and

nitrogenous bases within amino acids

Proved this hypothesis is POSSIBLE

RNA World Hypothesis

Earliest living cells were liposomes containing RNA

RNA can store information (like DNA) and catalyze reactions (like proteins)

RNA also capable of self replication (due to base pairing)

Ribozymes

RNA with protein-like enzyme activity

Four Stages leading up to

formation of life:

1. Abiotic synthesis of organic monomers

2. Abiotic synthesis of polymers

3. Formation of pre-cells

4. Self-replicating molecules

Protobiont (prelife) features

Boundary (membrane) separating interior/exterior

Polymers within had enzymatic function

Polymers within contained info

Ability to self replicate

First single celled organisms

Oldest fossils (3.5 billion years ago) = stromatolites

• Accumulation of sediment on bacterial mats

• Only Prokaryotes (single cell, no nucleus, no organelles)

from 3.5 to about 2.1 billion years ago

Stanley Miller's experiment simulated early Earth by exposing:

salt water, hydrogen, and to electricity and found that amino acids could be formed from these starting compounds in just a single week.

Types of variation

1. age group differences

2. Genetic differences (ex. sexual dimorphism)

3. Environmental differences (ex. polymorphism)

4. Chance (random effect of cell division, random changes in genetic code)