Things I Don't Know For BIO120 Midterm

Lamarckism

Modifications acquired during a species lifetime are able to be passed on to offspring.

Synonymous

Mutations that are not phenotypically expressed (silent mutation)

Can domesticated and wild animals hybridize to create a new species?

No.

Did Darwin conclude organisms contain limited amounts of heritable variation from his experiments with artificial selections species versus natural selection species?

No.

Homologous Trait

Inherited trait from a common ancestor.

What Did the Classical School Believe?

•  Low heterozygosity

• Low polymorphism

• Wild type is ‘normal’ genotype

• Selection typically negative

What Did the Balance School Believe?

• High heterozygosity

• High polymorphism

• Heterozygote advantage

• Selection favours diversity

Taxonomy

The science of identifying and grouping organisms (plants, animals, and microorganisms) based on shared traits and evolutionary history.

Darwin Predictions Arising from the Theory of Evolution (supported by a lot of evidence)

• Organisms on Earth change through time (across generations, and gradually*)

• Lineages split by speciation, resulting in the generation of biodiversity

• Novel (new) forms are derived from earlier forms

• All species are related, and are descended from a common ancestor

• Life on Earth is very old

• Adaptations result from natural selection

Sources of Evidence for Evolution (there are other sources but these are the main ones):

• Geology

• Homology

• Biogeography

• Domestication

Lessons From Geology

• Earth is very old

– Provides an immense amount of time for evolution to occur

• Novel forms are derived from earlier forms

– Evidence for transitional fossils linking features of seemingly dissimilar

relatives (e.g., ungulates and whales)

– Older fossils look less like living species

Lessons From Homology

• All species are related, and are descended from a common ancestor

– Shared ancestry is required to explain many instances of homologous similarity

• Organisms on Earth change through time

– When homologous traits have been modified for different purposes in different species, this provides evidence of evolutionary change

• Adaptations result from natural selection

– Vestigial traits can be explained by the presence of functional traits in ancestors, followed by degradation due to natural selection

Endemic

Something native (constantly) or physically present in a specific region.

Biota

Total collection of living organisms.

Lessons From Biogeography

• Lineages split by speciation, resulting in the generation of biodiversity

– Biogeographic distributions first alerted Darwin to the possibility that different species may arise from a common ancestor; recent work confirms evidence for past speciation events

• Adaptations result from natural selection

– Convergent evolution of distant relatives occurring in similar environments provides evidence for natural selection

Convergent Evolution

The independent development of similar features or traits in unrelated or distantly related species due to similar environmental pressures.

Divergent evolution

A biological process where a single ancestral species splits into two or more distinct descendant species that become increasingly different over time.

Transitional Evolution

The gradual process by which groups of organisms change over generations, displaying intermediate features that link ancestral species to their modern descendants.

Lessons From Domestication

• Organisms change through time

– Plant, animal breeders have documented evolutionary changes across generations in real time

• Lineages split by [pedigree breeding], resulting in the generation of [distinct breeds]

– Ability of breeders to produce wildly different plant, animal breeds shows that evolution can lead to species-level differences

• Adaptations result from [artificial] selection

– Artificial selection confirms that the mechanism of selection can lead to evolutionary change

– Only difference between natural, artificial selection is the agent of selection Evidence From Domestication

Parthenogenesis

Asexual reproduction in which embryo develops from an egg without fertilization (copy of parent).

Clonal propagation

Asexual reproduction not involving an egg.

Asexual Reproduction

Individual can create life by themselves without needing another individual. 

• 1 parent contributes genetic material

• No meiotic reductive division*

• Offspring are genetic replicas (clones) of parents

Sexual Reproduction

Have sexual with two different individuals, male and female. 

• 2 parents contribute genetic material to offspring

• Meiotic, reductive division to form gametes

• Fusion of gametes

Dioecious

Where sexual organs are found in different genders (example: human male and human female).

Hermaphrodite

Organisms with both female and male reproductive organs. (Ex: plants that have both male and female reproductive organs). 

Parthenogenesis

A form of asexual reproduction where an embryo develops from an unfertilized egg cell without any male genetic contribution

Costs of Sex

• Time and energy to find and attract mates

• Increased energetic costs of mating

• Risk of predation & infection

• Cost of producing males (males are not as beneficial as females in sexual organisms) 

• 50% less genetic transmission

• Break up of adaptive gene combinations

– Segregation, recombination

Benefits of Sex

• A sexual organisms have to hope from these mutations to occur spontaneously

• Sexual organisms through independent assortment and recombination can combine favourable genotypes to mutate alleles for fitness

Outcrossing (Term used for hermaphrodites)

• Mating with someone else

o Either by outbreeding or inbreeding

• Fusion of gametes from 2 parents

o Gametes derive from meiotic

reductive division

Selfing (self-fertilization): (Term used for hermaphrodites)

• Mating with yourself!

o Common in plants

• Fusion of gametes from 1 parent

o Gametes derive from meiotic

reductive division

• Most extreme form of inbreeding

• But NOT asexual reproduction as one is taking a random gametes from the male reproductive organ and random gametes from the female reproductive organ 

What Factors Lead to Inbreeding?

• Local population substructure enhances mating among relatives

• Hermaphroditic organisms have potential for self-fertilization

– Most plants, many animals

• In small populations, even random mating can lead to mating among relatives

Population Genetic Effects of Inbreeding

• Changes genotype frequencies

• Increases homozygosity

• Decreases heterozygosity (H)

• Does not directly change allele frequencies

• Does not change polymorphism (P) - variety in alleles and traits within a population 

Inbreeding Depression

Reduction in fitness of inbred offspring compared to outcrossed offspring.

The Genetic Consequences of Inbreeding

• Genotypic frequencies changed

– Heterozygosity (H) reduced by 50% per generation with self-fertilization

– Competition between homozygous genotypes (selection) & genetic drift of small

populations can reduce polymorphism (P)

• Homozygosity for deleterious recessive alleles

– Results in inbreeding depression

Inbreeding depression can change allele frequencies (P) or polymorphism

What is the most common form of genome mutation?

Point Mutation (Examples: Insertion, deletion, substitution, silent mutation, nonsense mutation)

Point Mutation

A genetic change where a single nucleotide base in a DNA or RNA sequence is changed, added, or deleted.

Nonsense Mutation

When a point mutation leads to a premature stop codon.

Somatic Cells

Most cells in the human body, EXCEPT REPRODUCTIVE CELLS.

What is true about Genetic Drift?

• Genetic drift can affect the frequency of traits with a visible phenotype

• Genetic drift occurs more rapidly in small populations

• Genetic drift results in the accumulation of neutral genetic differences between related species

• Genetic drift explains how mutations can spread to fixation when they are not advantageous

Is THE ABILITY to exhibit phenotypic plasticity is heritable?

True.

Molecular Clock

A technique that uses mutation rates in DNA, RNA, or proteins to estimate when two or more species diverged from a common ancestor.

What is the speed of mutation rate?

Slow, mutation takes time.

Primary Sex Characteristics

• Directly involved in production or transmission of gametes

Secondary Sex Characteristics

• Not involved in production or transmission of gametes

• Often only develop at sexual maturity, or during reproductive season

Darwin’s Theory of Sexual Selection 

• Differences in reproductive success among individuals due to competition for mates

• A “special case” of natural selection

Sexual Selection

All sexual selection involves competition between members of one sex for reproductive success, but this competition can take one of two forms (Intrasexual selection and intersexual selection).

Intrasexual Selection

• Individuals of the same sex (usually males) compete for access to mating or fertilization opportunities

• Aka “male-male competition”

Intersexual Selection

• Potential mates (usually females) choose among individuals of the other sex

• A.k.a. “female choice”

Acclimation

The short-term process in which an individual organism adjusts to changes in its environment, such as temperature, humidity, or altitude, to maintain its health and survival.

What is the main cause of sexual selection?

Males and females differ in investment in offspring production (almost always, females invest a whole lot more than males in offspring production).

Stochastic (unpredictable or random) evolutionary forces.

– Mutation

– Recombination

– Genetic drift

Deterministic (predictable or non-random) evolutionary force:

– Natural selection

Stochastic Processes Resulting in a Loss of Diversity

Genetic Drift:

• Stochastic changes in allele frequency due to random-(phenotype of organism) variation in fecundity & mortality

• Most important when populations are small

Population Bottlenecks:

• A single sharp reduction in abundance, usually followed by rebound

• Causes a loss of diversity

Founder Events:

• Colonization by a few individuals that start a new population

• Colonizing group contains only limited diversity compared to the source population

How many genomes do Eukaryotic cells have?

They have a normal genome which is in the nucleus and another genome which is in the mitochondria.

What did William Paley suggest pre-Darwin.

Paley argued that if there is so much complicity, there must be a designer. He used divine reasoning. 

Jean-Baptiste Lamarck

• First to use the term evolution

• Instead of envisioning that species were created by a designer and fixed from that point forward he had the idea that things could change over time. 

• First to provide a hypothesis for the causal mechanism:

– The inheritance of acquired characters

That it is passed on generation to generation 

Charles Lyell

• Focused more on rocks and geological processes 

• That the geological world was constantly changing 

• Principle of uniformitarianism

• Present day geological processes can explain the history of the Earth (erosion, deposit of sentiments, earthquakes, volcanoes, etc.)

• Before Lyell the world thought the world was made to be today since its creation

Uniformitarianism

The scientific principle that the same natural laws and processes operating in the universe today have always operated in the past and apply everywhere.

Darwin and Wallace’s Mechanism of Natural Selection

• Variation: Individual variation in a population

• Heredity: Progeny resemble their parents more than unrelated individuals

• Differential Fitness: Some forms are more successful at (surviving and) reproducing than

others in a given environment

– i.e., some forms are “more fit” than others

Important Elements of Darwin and Wallace’s Theory

1) Evolution occurs primarily at the level of populations (individuals don’t evolve) (this is where Lamarck went wrong) 

2) Variation is not directed by environment (individuals don’t induce adaptive

variation when needed)

3) Most fit type depends on the environment

4) ‘Survival of the fitter’: Evolution works with available variation, and will not

necessarily achieve perfection

Microevolution

Evolutionary patterns and processes observed within species.

Macroevolution:

Evolutionary patterns and processes observed among species.

Factors Influencing Genetic Diversity

I. Mutation - tends to increase diversity

II. Recombination - tends to increase diversity

III. Genetic drift - tends to decrease diversity

IV. Natural selection - tends to increase or decrease diversity

V. Migration - tends to increase diversity

Negative (purifying) selection

• Mutations that reduce fitness are removed by natural selection

• Decreases genetic variation in populations

Positive (directional) selection

• Mutations that increase fitness will eventually become fixed in a population

• Decreases genetic variation in populations

Selection favoring maintenance of multiple alleles (balancing selection)

• Natural selection can act to maintain diversity over the long term (e.g., heterozygote advantage)

• Increases (or retains) genetic variation in populations

• Maintains balance between both alleles throughout the generations 

Fixation

 Occurs when a polymorphic locus becomes monomorphic due to the loss of all but one allele. (note: can occur due to natural selection or genetic drift).

Monomorphism

When two alleles are present and there is no variation (opposite of polymorphism).

Selective Sweep

Occurs when selection causes a new mutation to increase in frequency so quickly that nearby alleles “hitchhike” and also increase in frequency.

Hitchhike

When a neutral or even harmful allele increases in frequency in a population not because it provides any survival advantage, but because it sits physically close to a beneficial gene on the same chromosome.

Genome

The entirety of an organism’s DNA*

– Includes genes and non-coding regions

Sources of Genetic Variation

1) Mutation

2) Independent assortment

3) Recombination

Theory of blending inheritance (1800s) - Pre Darwinian Thinking

Postulated that factors from both parents mix together irreversibly

Key Conclusions from Mendel’s Pea Experiments

1) Inheritance is determined by discrete particles

• Genes

2) Each diploid organism carries two copies (alleles) of each gene

• Alleles can exhibit dominance / recessivity

• Gametes contain only one allele per gene

3) Gametes fuse to make offspring

• Sperm / pollen fuses with egg / ovule

4) Offspring inherit one gamete from each parent at random

• One allele per gene at random from each parent

Gamete

A mature reproductive or sex cell that unites with another cell of the opposite sex during fertilization to form a new individual.

Discrete (Mendelian) variation

• ‘Mendelian’ genetics

• Genes of major effect

• In these systems, we can measure:

– dominance and recessiveness

– the spread of alleles; changes in allele frequency

Continuous (Quantitative) variation

• Quantitative genetics

• Many genes each with alleles of small effect, important environmental effects

• In these systems, we can measure:

– selection response as change in average trait value

Bottleneck Effect

A type of genetic drift where a major event abruptly kills most of a population.

Negative frequency-dependent selection

An evolutionary process where the fitness of a trait, gene, or phenotype increases as it becomes rarer in a population.