Biology 1M03 Midterm 1

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Cell Theory

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All cells have a membrane and contain organized information. All organisms are made of cells. All cells come from preexisting cells. (all descended from zygote)

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Evaluation of Cell Theory

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By broth experiment: cells grow in sterilized broth sample that is unsealed and not in the sealed. (Louis Pasteur)

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Organisms

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Any continuous living system but this definition is up to philosophical debate

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Theory of Evolution by Natural Selection

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"Discovered" independently by Darwin and Wallace. All species related through common ancestor. Characteristics of species can be modified (change in a allele frequencies)

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Evolution

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Species are related to one another and change through time Change in allele frequencies over time

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Natural Selection

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Explanation for evolution,

1) Variation

2) Heritability

3) Fitness effects and competition

4) Individuals who survive best and reproduce most have the traits that will be passed down (non-random)

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Characteristics of Natural Selection

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-Influences Fitness

-is heritable (coded from DNA and passed from gen. to gen.)

-traits become more common in a pop. over time

-acts on individuals but evolution happens on a population level

-heritable traits results in differential success in reproduction and higher fitness

-causes variation!

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Artificial Selection

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Selection (selected for mating) for certain traits in animals/plants by humans. Ex: domestication of animals (pigs)

Can change entire populations in time!

Can cultivate for extreme phenotypes!

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Unintended Artificial Selection

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Occurs with human predation,

-leads to genetic modification (eg: domestication of crops)

-hunting and fishing effecting evolution of size (ie: cod)

*Different from GMO

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Species

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Two species are different if they cannot interbreed with each other/their offspring are inviable (but there are exceptions in hybrid zones)

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Speciation

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One species through time diverging into two because of selection pressures

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Molecular Variation

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Occurs in nucleotides! Can compare genetic sequences and the more similar they are the more closely related the two species are.

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Horizontal (Lateral) Gene Transfer

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Common in bacteria: can reproduce through budding or sexually (vertigo gene transfer) but also through their environment.

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Endosymbiosis

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An association between species in which one lives inside the cell or cells of the other. (endosymbiosis theory: mitochondria and chloroplasts originated by primary and secondary endosymbiosis and therefore have their own DNA)

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Hybridization

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Breeding of two different strains, populations, or species

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Lamarkism

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Inheritance of required characteristics: if a trait is not used it will be lost. (this has been refuted with experimentation)

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Homology

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Similarity among organisms of different species due to their inheritance from a common ancestor. Features that exhibit such similarity are said to be homologous. (ex: genetic homology, system of DNA and RNA present in all life)

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Development Homology

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A similarity in embryonic form or in the fate of embryonic tissues that is due to inheritance from a common ancestor.

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Structural Homology

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Similarities in organismal structures (limbs, shells, flowers) that are present because of inheritance from a common ancestor.

ie: vertebrate limbs modifications of the same number and arrangement of bones)

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Vestigial Traits

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Traits that are old and no longer used but still present.

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Evidence for Evolution

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Fossils, extinction events, transitional form fossils, vestigial traits, speciation in real time (by hybridization, polyploidization, geographic speciation etc.)

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Incipient Species

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Species that are divulging from each other.

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Microevolution vs. Macroevolution

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There is no real difference between them

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Fitness

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The ability of an individual to produce viable offspring relative to others of the same species

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Adaptation

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Any heritable trait that increases the fitness of an individual with that trait, compared with individuals without that trait, in a particular environment.

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Hardy Weinburg Principle

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A principle of popular genetics stating that genotype frequencies in a large population do not change from generation to generation in the absence of evolutionary processes (ex: mutations, migration, genetic drift, random mating, and selection) A null hypothesis that predicts genotype frequencies given certain allele frequencies.

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Inbreeding

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Mating between closely related individuals. Increases homozygosity of a population and often leads to decline in the average fitness (inbreeding depression).

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Non-Random Mating

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In many cases, females don't choose mates at random, but actively choose certain males. Three mechanisms: inbreeding, assortative mating, and sexual selection.

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Gene Flow

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The movement of alleles between populations; occurs when individuals leave one population, join another and breed. Tends to homogenize gene frequencies.

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Genetic Drift

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Random sampling error of alleles between generations. Change (drift up and down) in allele frequencies due to random events. Leads to fixation or loss of alleles. (stronger influence in small populations) Removes genetic variation and moves towards extreme phenotypes

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Mathematical Model of analyzing allele frequencies + assumptions

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Imagined all gametes produced in each generation go into a single group called a gene pool and then combine randomly. (Hardy-Weinburg) Assumes no 1) natural selection 2) genetic drift 3) gene flow 4) mutation 5) biased mating

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Major Histocompatibility Locus (in humans)

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The immune system (basically! can tell which cells are from the body and which are from outside it) Women off the pill attracted to the scent of a man who has opposite MHL genes because heterozygosity is better for health!

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Types of Natural Selection

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1) Balancing Selection

2) Directional Selection

3) Stabilizing Selection

4) Disruptive Selection

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Balancing Selection

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A pattern of natural selection in which no single allele is favoured in all populations of a species at all times. Instead, there is a balance among alleles in terms of fitness and frequency.

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Heterozygote Advantage

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A pattern of natural selection that favours heterozygous individuals compared with homozygotes. Tends to maintain genetic variation in a population. (aka heterozygote superiority) EX: sickle cell anemia

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Frequency Dependent Selection

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A pattern of selection in which certain alleles are favoured only when they are rare; a form of balancing selection (fitness is higher in rare phenotypes)

-maintain overall genetic variation

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Directional Selection

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A pattern of natural selection that favours one extreme phenotype with the result that the average phenotype of a population changes in one direction. Generally reduces overall genetic variation in a population. Alleles become fixed or lost.

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Stabilizing Selection

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A pattern of natural selection that favours phenotypes near the middle of the range of phenotypic variation. Reduces overall genetic variation in a population.

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Disruptive Selection

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A pattern of natural selection that favours extreme phenotypes at both ends of the range of phenotypic variation. Maintains overall genetic variation in a population. Requires individuals with one extreme to start mating preferentially with individuals with the other extreme.

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Founder Effect

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Change in allele frequencies that often occurs when a new population is established from a small group of individuals (founder event) due to sampling error (ie. the small group is not a representative sample of the source population)

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Genetic Bottleneck

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A reduction in allelic diversity resulting from a sudden reduction in the size of a large population (population bottleneck) due to a random event.

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Sexual Selection

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A pattern of natural selection that favours individuals with traits that increase their ability to obtain mates. Acts more strongly on males than females.

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Male-Male Competition

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Territoriality and competition for mates between males. Variation in reproductive success.

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Sexual Dimorphism

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Any trait that differs between males and females of the same species.

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Species

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Evolutionary independent populations or groups.

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Prezygotic Isolation

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Reproductive isolation resulting from any one of several mechanisms that prevent individuals of two different species from mating

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Postzygotic Isolation

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Reproductive isolation resulting from mechanisms that operate after mating of individuals of two different species occurs. The most common mechanisms are the death of hybrid embryos or reduced fitness of hybrids.

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Species Concepts

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1) Biological

2) Morphological

3) Ecological

4) Phylogenetic

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Biological Species Concept (BSC)

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The definition of a species as a population or group of populations that are reproductively isolated from other groups. Members of a species have the potential to interbreed in nature to produce viable, fertile hybrid offspring but cannot produce said offspring with members of other species.

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Problems with Biological Species Concept

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Many species do hybridize to a limited extent as observed in nature.

Does not take into account asexual species or geographic isolation of species that would be exceptions of this. (ligers)

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Morphological Species Concept (MSC)

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The definition of a species as a population or group of populations that have measurably different anatomical features from other groups. (Also called morphospecies concept.)

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Problems with Morphospecies Concept

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Features used to distinguish species are rather subjective.

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Ecological Species Concept (ESC)

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The definition of a species as a set of organisms exploiting a single set of resources, having the same range of environmental tolerances, and facing the same predators and parasites.

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Problems with Ecological Species Concept

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How exactly can you define it in the context of geographic separation? Are they the same species if they inhabit the same environment but on two different continents?

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Phylogenetic Species Concept (PSC)

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The definition of a species as the smallest monophyletic group in a phylogenetic tree.

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Phylogenetic Tree

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A diagram that depicts the evolutionary history of a group of species and the relationships among them

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Monophyletic Group

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An evolutionary unit that includes an ancestral population and all of its descendants but no others. AKA a clade or lineage (one snip test on phylogenetic tree)

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Synapomorphy

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A trait unique to a monophyletic group

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Problems with Phylogenetic Species Concept

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Can lead to over diagnosing what a species is.

(Splitters: division of one species into many)

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Sub-Species

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Populations that live in discrete geographic areas and have their own identifying traits but are not distinct enough to be considered a separate species.

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Allopatry

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Condition in which two or more populations live in different geographic areas

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Vicariance

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The physical splitting of a population into smaller isolated populations by a geographic barrier. (stops gene flow)

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Cryptic Species

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A species that cannot be distinguished from other species by easily identifiable morphological traits.

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Biogeography

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The study of how species and populations are distributed geographically.

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Kin Selection

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A form of natural selection that favours traits that increase survival or reproduction of an individual's kin at the expense of the individual.

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Dispersal

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The movement of individuals from their place of origin (birth, hatching) to a new location. (Physical barrier is older than the speciation event)

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Sympatry

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Condition in which two or more populations live in the same geographic area or close enough to permit interbreeding

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Historical Contingency

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The theory that the paths that life can evolve are constrained by historical events that are often random. "If you rewound evolution like a tape and played it again would life evolve the same way or in a very different manner?"

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Sympatric Speciation

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Occurs when gene flow is possible but not actually occurring. New species arise because genetic barriers not physical ones! (populations live in same geographic area)

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Polyploid

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An organism with more than two full sets of chromosomes. (tetraploid, octoploid, etc.)

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Speciation by Polyploidization

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Mutation of individuals having more than two sets of chromosomes reducing gene flow between mutant and normal individuals! (Ex: tetraploid and diploid individuals rarely produce fertile offspring when they mate therefore becoming reproductively isolating)

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Autopolyploid

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"same many-form" individuals are produced when a mutation results in a doubling of chromosomes number and the chromosomes all come from the same species.

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Allopolyploid

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"different many-form" individuals are created when parents that belong to different species mate and produce an offspring where chromosome number doubles. Allopolyploid individuals have chromosome sets from different species.

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Reinforcement

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In evolutionary biology, the natural selection for traits that prevent inbreeding between recently diverged species

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Hybrid Zones

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A geographic area where interbreeding occurs between two species, sometimes producing fertile hybrid offspring.