BIOL 1P92 Midterm
Evolution
- heritable change in one or more characteristic of a population or species from one generation to the next
Macroevolution vs microevolution
Macro: viewed on a larger scale
- formation of a new species or groups of related species
Micro: viewed on a small scale
- changes in a single gene or allele frequencies in a pop. over time
Species
- group of related organisms that share a distinctive form
Population:
all members of the same species that live in the same area at the same time and have the opportunity to interbreed
T/F: If they cannot produce viable offspring they are not considered part of the same species
TRUE
Who are four of the scientists who set the stage:
John Ray:
Carl Linnaeus:
George Buffon:
Jean-Baptiste Lamarck:
Who is another scientist who set the stage: *____ Darwin (not Charles)
- Erasmus Darwin
- an early advocate of evolutionary change and suggested life on Earth could have descended from a common ancestor
- made many observations based on selective breeding practices ("Artificial cultivation")
What is the Uniformitarianism hypothesis:
- from geology
- slow geological processes lead to substantial change
What is Catastrophism:
- which fit with religious teachings
- earth is 6,000 years old and only catastrophic events have changed its geological structure
Charles Darwin: What was his nationality, when was he born, what theory did he play a central role in
- British
- naturalist
- 1809
- central role in developing the theory that existing species have evolved from pre-existing species (natural selection)
- voyage on HMS Beagle from 1831-1836
- Galapagos finches
T/F: Papers by Darwin and Wallace both published, but were not well recognized
- TRUE
- went against religious teachings
What is one of the most important contributions to our understanding of biology
- On the Origin of Species (1859)
Who said: "The theory of descent with modification through variation and natural selection"
Charles Darwin
Evolution occurs from generation to generation due to two interacting factors:
1. Variation: in traits that occur among individuals and are heritable from parents to offspring
2. Natural Selection: individuals with traits that make them better suited to the environment flourish and reproduce, while others are less likely to survive and reproduce
(favourable traits become more prevalent in a pop. over time)
Genetic variation is an ___________ force in evolution as it allows natural selection to __________ or ____________ frequency of alleles ___________ in the population
Genetic variation is an important force in evolution as it allows natural selection to increase or decrease frequency of alleles already in the population
How is genetic variation advantageous to a population:
- it enables some individuals to adapt to the environment while maintaining the survival of the population
- caused by mutation:
- Random mating, random fertilization, and recombination between homologous chromosomes during meiosis
Spirit Bears example: Recessive mutation in the Melanocortin 1 Receptor gene
- Picture of a black fur bear and a white fur bear (but BOTH are black bears)
- The 'white' bear has a mutation in the melanocortin 1 receptor gene
- The likelihood of a spirit bear arising is quite rare -but might be more likely if there was more snow, because then the white fur would be an advantageous trait to have
Evolutionary Adaptation by natural selection example: Peppered Moths
- in england
- Coal burning, soot in the air that settles on trees
- Originally the peppered moths were majorly white although there was a few darker ones
- When the trees turned dark the white moths were eaten more by the birds
- Gradual shift to dark moths
Lamarckian vs. Darwinian views of evolution:
While both Lamarck and Darwin proposed theories of evolution, the key difference lies in how they believed traits were acquired and passed on:
Lamarck believed organisms could develop traits during their lifetime based on environmental needs and pass those "acquired characteristics" to their offspring EX.) STRETCHING OF TRUNKS
Darwin's theory of natural selection states that variations already present within a population are selected for by the environment, meaning only the advantageous traits are passed on to the next generation, not traits acquired during an individual's life EX.) THAT SLIGHTLY LONGER TRUNKS OBTAINED MORE FOOD
Types of Evidence: Beak Depth on Daphne Major
- medium ground finches on Daphne Major
- a model of natural selection
- beak depth is a heritable trait
- provides evidence of natural selection in action
- fewer seeds on the island from a drought - had to eat larger seeds so beaks over generations lengthened
Types of Evidence: Selective Breeding
- kind of manipulating natural selection (the traits that humans like and breed may have been eliminated via natural selection in the environment)
- differs from natural selection in how the parents are chosen - desirable phenotypes chosen by breeders
Type of Evidence: Biogeography
- study of the geographic distribution of extinct and living species
- isolated continents have evolved their own distinct plant and animal communities
Endemic - naturally found only in a particular location
**Different pressures in different environments**
Types of Evidence: Convergent Evolution
- two species from different lineages have independently evolved similar characteristics because they occupy similar environments
- they are not related
- different species, different evolutionary traits
SAME SOLUTIONS TO SAME PROBLEMS, BUT DIFF ANIMALS
ex.) hummingbirds and butterflies
- hovering, long and thin beak or probescis
ex.) English Ivy and wintercreep
- to climb up supports
Types of Evidence: Fossil Record (transitionary forms)
• Fossils are compared according to their age, from oldest to youngest
• Successive evolutionary change becomes apparent
• Transitional form: Fossils that provide a link between an ancestral form and its descendants
What is a Fishapod (Tiktaalik Roseae)
- a semi-aquatic amphibian
• Transitional form between fishes and tetrapods(walk on all 4 limbs)
• Had broad skull, flexible neck, eyes on top of head, primitive wrist, and five finger-like bones - but also fin-like structure
• Could peek above water and look for prey
Types of Evidence: Homology
- fundemental similarity due to descent from a common ancestor
- homology may be:
1. Anatomical
2. Developmental
3. Molecular - similar sequences
Examples of Vestigial structures: remnants or 'left-over' structures - no real pressure to get rid of it
- humans: bony tail in embryo and mucles to wiggle ears in adult
- manatees: fingernails on the flippers
What are HOMOLOGOUS GENES:
- two or more genes derived from the same ancestral gene
What are ORTHOLOGS
- homologous genes in different species
What are PARALOGS
- two or more homologous genes within a single species
produced by gene duplication events
What are GENE FAMILIES
- two or more paralogs within the genome of a single organism
What are globin genes
Allows for specialized function, expression at different times or in different tissues
Horizontal Gene Transfer or Vertical Gene Transfer
Vertical evolution: new species arise from pre-existing species by accumulation of genetic changes
Horizontal gene transfer: an organism incorporates genetic material from another organism, without being its offspring
• Same or different species
What is a GENE
- a DNA sequence that codes for an RNA or protein
- contributes to the characteristics and traits of an organism
- a gene is found at a chromosomal locus
- different variants of a gene are called alleles
________ organisms typically have _____ copies of every gene
DIPLOID organisms typically have TWO copies of every gene
Genotype vs. Phenotype:
Genotype: the combination of alleles that a person possesses at a single locus or number of loci
Phenotype: observable characteristics of a person, organ, or cell
POLYMORPHISM
- many traits or genes display variation within a population
- genes are usually polymorphic
Most variation (polymorphism) is due to _________________________ (SNPs)
Most variation (polymorphism) is due to SINGLE NUCLEOTIDE POLYMORPHISM (SNPs)
Explain the HARDY-WEINBURG EQUATION: highly impractical but useful
• Describes a mathematical relationship between allele frequencies and genotype frequencies in a population
• The Hardy-Weinberg equation states that:
• p2 and q2 are the genotype frequencies of the homozygotes
• 2pq is the genotype frequency of heterozygotes
○ Multiplied by 2 because two different gamete combinations produce heterozygotes
predicts that allele and genotype frequencies will remain the same generation after generation, if the population is in equilibrium (= 0.5)
• No evolutionary mechanisms acting on the population
• Conditions that must be met for equilibrium:
1. No new mutations
2. No natural selection
3. Large population
4. No migration between different populations
5. Random mating
what is endemic
- naturally found only in a particular location
convergent traits can also be called _____________ structures
ANALOGOUS structures
What is an example of convergent traits
- hummingbirds and hummingbird moth
Hummingbirds:
- ability to beat their wings rapidly and their long thib beak
Moth:
- have a proposcis
T/F, homology may be:
- anatomical
- developmental
- molecular (similar sequences)
TRUE
what is a gene:
A DNA sequence that codes for an RNA or protein
- found at a chromosomal locus
- contributes to the characteristics and traits of an organism
different variants of a gene are called alleles
T/F, diploid organisms have two copies of every gene
TRUE
if alleles are identical = ______________
if alleles are different = ______________
if alleles are identical = homozygous
if alleles are different = heterozygous
what are POPULATIONS
- Group of individuals of the same species that occupy the same environment and can interbreed with one another
- Some species occupy a wide geographic range and are divided into discrete populations
- Populations can change in size, geographic location, and genetic composition
T/F, large, healthy populations exhibit a high level of genetic diversity
TRUE
Disequilibrium
- populations rarely achieve equilibrium
why is Hardy-Weinburg equilibrium a useful concept?
• When researchers examine allele and genotype frequencies, and find that a population is not in equilibrium, this indicates a condition is being violated
○ It acts as a baseline to identify if a population's allele frequencies are changing over time, indicating potential evolutionary forces at play
What is microevolution
- changes in a population's gene pool from generation to generation
- due to:
- introduction of new genetic variation: occur at a low rate, do not significantly disrupt HW equilibrium
- mechanisms that alter the prevalence of an allele or genotype: potential for widespread genetic change
what is natural selection
process by which beneficial traits that are heritable become more common in successive generations
- over time, natural selection results in adaptations: changes in populations of living organisms that promote their survival and reproduction in a particular environment
T/F, reproductive success is a KEY piece of natural selection
TRUE
what is REPRODUCTIVE SUCCESS
- the likelihood of an individual contributing fertile offspring to the next generation
what are the two categories of traits of reproductive success
1. Traits that make organisms better adapted to their environment and more likely to survive to reproductive age
2. Traits directly associated with reproduction, such as those that affect the ability to find a mate or produce viable gametes and offspring
modern description of natural selection
- allelic variation arises from random mutation
- some alleles encode proteins that enhance survival or reproductive success
- individuals with beneficial alleles are more likely to survive and pass these alleles to the next generation
- over time, allele frequencies change through natural selection, altering the characteristics of a population
FITNESS meaning
- relative likelihood that a genotype will contribute to the gene pool of the next generation as compared to other genotypes
- measure of reproductive success
What are the four NATURAL SELECTION PATTERNS (DSDB)
1. Directional selection
2. Stabilizing selection
3. Disruptive/Diversifying selection
4. Balancing selection
Pattern of natural selection: Directional Selection
• Individuals at ONE EXTREME of a phenotypic range have greater reproductive success in a particular environment
• Initiators:
• Prolonged environmental change
• New allele with higher fitness introduced by mutation
• Causes the favoured allele to eventually predominate in a population
• May lead to a monomorphic gene (no variation)
Pattern of Natural Selection: Stabilizing Selection
• Favours the survival of individuals with intermediate phenotypes and selects against those with extreme phenotypes
• Example: Clutch size
• Too many eggs à offspring die due to lack of care and food, strain may decrease parent survival
• Too few eggs à does not contribute enough to next generation
Pattern of natural selection: Diversifying selection
• Favours the survival of two or more different genotypes that produce different phenotypes
• Likely to occur in populations that occupy heterogeneous environments
• Fitness value of one genotype is high in one environment, but lower in a different environment, and vice versa
• Members of the populations can freely interbreed
Pattern of natural selection: Balancing selection
• A type of natural selection that maintains genetic diversity in a population
• Over many generations results in balanced polymorphism: Two or more alleles are maintained in a population over
the course of many generations
• Two common ways this occurs:
1. Heterozygote advantage: Heterozygotes for a trait have the highest fitness
○ E.g. Sickle cell disease
2. Negative frequency-dependent selection: The fitness of a genotype decreases when its frequency becomes higher
○ Rare individuals have a higher fitness than common individuals
○ E.g. Predator & prey
Sexual Selection
- type of natural selection
- individuals with certain traits are more likely to engage in successful reproduction than other individuals
- often affects males more than female
SEXUAL DIMORPHISM
- significant difference between the appearances of the two sexes within a species
Intrasexual selection
- between members of the same sex
- males directly compete for mating opportunities or territories
ex.) horns in male sheep, antlers in male moose, male fiddler crab enlarged claws
Intersexual selection
- between members of the opposite sex
- aka mate choice
- often results in showy characteristics in males
Cryptic female choice:
- a type of intersexual selection that occurs by female-driven mechanisms at or after mating
• Leads to differential success of sperm in fertilizing the egg
• May sometimes function to inhibit inbreeding
ex.) Female guppies will control copulation to receive less sperm from less colourful males
The Cost of Reproduction:
• Sexual selection can explain traits that decrease survival but increase reproductive success
• If trait increases predation, its frequency may be lower in environments where predators are abundant
what is GENETIC DRIFT
• Changes in allele frequencies due to random chance
• Unrelated to fitness
• Favours either loss or fixation of an allele
• Frequency reaches 0% or 100%
• Effect is strongest in small populations, where infrequently occurring alleles face a greater chance of being lost
• Reduces genetic diversity
• May quickly alter allele frequencies after population reduction, e.g.:
• Population bottleneck
• Formation of a founder population
what is BOTTLE EFFECT
a mechanism that drives genetic drift
- Population size is reduced dramatically, and then rebuilds
- Randomly eliminates members without regard to genotype
- When the population is small, genetic drift may rapidly reduce the genetic diversity
- Surviving members may have allele frequencies different from original population
explain the founder effect
- also causes genetic drift
• Small group of individuals separates from a larger population and establishes a colony in a new location
• Relatively small founding populations are expected
to have less genetic variation than original population
• By chance, allele frequencies in founding population may differ markedly from original population
• Fewer individuals to select from, allele frequencies differ from the original one given time
• Amish of Lancaster descended from 3 couples
• Ellis-van Creveld syndrome rare in human population
• Traced back to 1 of the 3 original couples
what is gene flow
- transfer of alleles into or out of a population
occurs when: fertile individuals move between populations having different allele frequencies
what does migration tend to REDUCE and what does it tend to INCREASE
• Reduce differences in allele frequencies between the two populations
• Increase genetic diversity within a population
what is nonrandom mating and what are the two forms that it occurs in
• Individuals choose their mates based on their genotypes or phenotypes
• Affects the balance of genotypes predicted by Hardy-Weinberg
• Occurs in two forms:
1. Assortative / disassortative mating
2. Inbreeding
Assortative and Disassortative Mating:
• Assortative mating
• Disassortative mating
Assortative mating: Individuals with similar phenotypes are more likely to mate
• Increases the proportion of homozygotes
- a female is choosing a mate that looks more similar to her - diff than sexual selection
• Disassortative mating: Dissimilar phenotypes mate preferentially
• Increases heterozygosity
Inbreeding:
- does inbreeding plumet or raise genetic diversity
• Mating of two genetically related individuals
• Increases homozygosity and decreases heterozygosity
• May have negative consequences with regard to rare recessive alleles
- it plumets genetic diveristy
T/F, inbreeding occurs if: homozygous offspring have a lower fitness value, inbreeding lowers the mean fitness of a population
TRUE
what animal is an example of inbreeding
florida panther
The Earth is believed to have formed from the aggregation of planetesimals(rocks) ~____ BYA
4.55 BYA (billion years ago)
life emerged between ____ and ____ BYA
4 and 3.5 billion years ago
DNA is made by ________________ process
DNA is made into RNA by _________________ process
RNA is made into proteins by _________________
DNA is made by REPLICATION process
DNA is made into RNA by TRANSCRIPTION process
RNA is made into proteins by TRANSLATION process
• Organic molecules and macromolecules formed spontaneously and slowly accumulated in early oceans
= Prebiotic soup
where did this "prebiotic soup" originate
1. Reducing atmosphere hypothesis
2. Extraterrestrial hypothesis
3. Deep-sea vent hypothesis
what is a PROTOBIONT:
An aggregate of prebiotically produced molecules and macromolecules that have acquired a boundary, such as a lipid bilayer
• Allows it to maintain an internal chemical environment distinct from that of its surroundings
what are the four characteristics of a protobiont:
1. A boundary separating external environment from internal contents
2. Polymers inside containing information
3. Polymers inside with enzymatic function
4. Capable of self-replication
T/F: living cells may have evolved from LIPIDS and COACERVATES
true
what are the three RNA functions
1. Ability to store information
2. Capacity for self-replication
3. Enzymatic function (ribozymes)
(DNA and proteins cannot do all 3 functions)
What nucleic acids do DNA and RNA have
DNA: Adenine, Thymine, Cytosine, Guanine
RNA: Adenine, Uracil, Cytosine, Guanine
Advantages of DNA/RNA/Protein world
• Information storage
• Incorporation of DNA to store information would relieve RNA of this function, and allow RNA to perform more complex catalytic functions
• DNA has increased stability - two strands!
• Ancestral RNA may have been able to make DNA from RNA template
• Metabolism and other cellular functions
• Proteins have vastly greater catalytic potential
• Proteins can perform other tasks – structural, transport, etc.
• Ancestral RNA likely contributed to polypeptide formation
○ Still plays central role in protein synthesis!
WHAT DOES LUCA STAND FOR
= last universal common ancestor
fossils are formed in ________________ rock
SEDIMENTARY rock
what are the FOUR layers of sedimentary rock:
1. Sedimentation: Eroded sediments end up in the water and begin to settle
2. Compaction: with time, more layers pile up and presses down the lower layers
3. more layers (strata) and further compaction forces out water of the layers
4. Salt crystals glue the layers together (cementation). Rock mass formed its sedimentary.
radioisotope dating looks at what??
Fossil age is estimated by radiometric dating
(measures the amount of a radioisotope and its decay product)
Each radioisotope has a unique _______________ that can be used for dating
Each radioisotope has a unique HALF-LIFE that can be used for dating
what is HALF-LIFE
time required for exactly one-half of original isotope to decay
name the factors that affect the fossil record: A.G.E.N.T.S (plus P)
A - anatomy
G - geological processes
E - environment
N - number
T - time
S - size
P - paleontology
what are the four eons of Earth's timeline
- Hadean
-Archaean
- Proterozoic
- Phanerozoic
= make up the Precambrian era
what are 6 ENVIRONMENTAL CHANGES
1. Temperature
2. Atmosphere
3. Landmasses
4. Floods and glaciations
5. Volcanic eruptions
6. Meteoric impacts
what are the four periods of Earth
1. Pre-Paleozoic period
2. Paleozoic period (Pangaea)
3. Mesozoic period
4. Cenozoic period (modern Earth)
what are the two domains of prokaryotic life
- Archaea and bacteria