Unit 4 Peterson BIOL 214

Microevolution

Heritable change in the genetics of a population

Population

All the individuals of a single species that live together in the same place and time

Phenotypic variation

Differences in appearance or function that exist within populations of all organisms

Quantitative variation

Variation that is measured on a continuum rather than in discrete units or categories

Qualitative variation

Variation that exists in two or more discrete states

Polymorphism

Existence of many discrete variants of a character

Genetic variation

Causes production of new alleles and rearrangement of existing alleles

Gene pool

Sum of all copies at all gene loci in all individuals

Genotypic frequencies

Percentage of individuals that possess each genotype

Allelic frequencies

The abundances of the different alleles

Hardy-Weinberg equilibrium

Specifies the conditions under which a population of diploid organisms achieves genetic equilibrium

Genetic equilibrium

The point at which neither allele frequencies nor genotype frequencies change in succeeding generations

Mutation

Spontaneous and heritable change in DNA

Deleterious mutations

Mutations with harmful effects

Lethal mutations

Mutations that cause death

Neutral mutations

Mutations that are neither harmful nor helpful

Advantageous mutations

Mutations that have beneficial effects

Gene flow

Change in allele frequencies as individuals join a population and reproduce

Genetic drift

Random changes in allele frequencies caused by chance events

Population bottlenecks

A random disaster or stressful factor leads to a reduction in population size

Founder effects

A few individuals colonize a distant locality and start a new population

Natural selection

Different survivorship/reproduction of individuals with different genotypes

Relative fitness

Number of surviving offspring that an individual produces compared with others in the population

Directional selection

One end of the phenotypic spectrum has the highest relative fitness

Stabilizing selection

Middle of the phenotypic spectrum has the highest relative fitness

Disruptive selection

Both ends of the phenotypic spectrum have the highest relative fitness

Non-random mating

Choice of mates based on their phenotype and genotypes

Effect of non-random mating on allele frequencies

No direct effect on allele frequencies but does prevent genetic equilibrium

Negative effects of non-random mating

May have negative effect on fitness through the expression of recessive phenotypes

Sexual selection

Favors showy structures and elaborate courtship behavior

Sexual dimorphism

Differences in the size or appearance of males and females

Intersexual selection

Selection based on the interactions between males and females

Intrasexual selection

Selection based on the interactions between members of the same sex

Inbreeding

Genetically-related individuals mate with each other

Effect of inbreeding on genotypes

Increases frequency of homozygous genotypes and decreases the frequency of heterozygotes

Diploid organisms

Can hide recessive alleles from natural selection

Balanced polymorphism

Two or more phenotypes are maintained in fairly stable proportions over many generations

Heterozygote advantage

Heterozygotes have higher relative fitness than either homozygote

Sickle cell example

When not infected, heterozygotes have normal red blood cells; when infected, they have sickle-shaped red blood cells that kill parasites

Frequency-dependent selection

A form of natural selection in which rare phenotypes have a selective advantage simply because they are rare

Neutral variation hypothesis

Some of the genetic variation at certain loci is selectively neutral

Adaptive trait

Any product of natural selection that increases the relative fitness of an organism in its environment

Adaptation

Accumulation of adaptive traits over time

Limitations of adaptation

No organism can be perfectly adapted to its environment because the environment changes over time

Natural selection and mutations

Natural selection acts on new mutations and existing genetic variation

Morphological adaptations

Adaptive changes in the morphology of an organism are often based on small modifications of existing structures

Speciation

Process of species formation

Morphological species concept

All individuals of a species share measurable traits that distinguish them from individuals of other species

Biological species concept

Groups of interbreeding natural populations that are reproductively isolated from other such groups

Genetic cohesiveness

Populations of the same species experience gene flow which mixes their gene pool

Phylogenetic species concept

Using both morphological and genetic sequence data to define species

Subspecies

Local variants of a species/populations within species often differ both genetically and phenotypically

Ring species

Species with a geographical distribution that forms a ring around uninhabitable land

Clinal variation/cline

Smooth pattern of variation across a geographical gradient

Reproductive isolation mechanisms

Prevent individuals of different species from mating and producing successful progeny

Prezygotic isolating mechanisms

Prevent mating before fertilization and production of a zygote

Ecological isolation

Species live in different habitats

Temporal isolation

Species mate at different times of the year

Behavioral isolation

Species cannot communicate due to different signals

Mechanical isolation

Species cannot physically mate

Gametic isolation

Non-matching receptors on gametes

Postzygotic isolating mechanisms

Prevent successful development after fertilization

Hybrid inviability

Hybrid does not complete development

Hybrid sterility

Hybrid cannot produce gametes

Hybrid breakdown

Reduced survival or fertility in subsequent generations

Allopatric speciation

Speciation where a population is divided physically leading to geographical isolation

Secondary contact

Contact after a period of geographic isolation to assess genetic divergence

Hybrid zones

Regions where two species meet again and some interbreeding occurs

Reinforcement

Enhancement of reproductive isolation that had begun to develop while populations were geographically separated

Sympatric speciation

Speciation where reproductive isolation occurs between distinct subgroups within one population

Three genetic mechanisms can lead to reproductive isolation:

Genetic divergence between allopatric populations, Polyploidy in sympatric populations, Chromosome alterations

Genetic divergence between allopatric populations

Geographically separated populations inevitably accumulate genetic differences through the action of mutation, genetic drift, and natural selection

Polyploidy

Condition where organisms have more than two complete sets of chromosomes

Autoploidy

A diploid individual produces a tetraploid offspring

Allopolyploidy

Two closely related species hybridize and form a polyploid offspring

Chromosome alterations

Changes in chromosome structure that can lead to reproductive isolation

Population dynamics

How the characteristics of populations change through time and vary from place to place

Geographical range

Overall spatial boundaries within which a population lives

Population size

Number of individuals in a population at a specified time

Population density

Number of individuals per unit area

Mark-release-capture

Method to estimate population size by capturing, marking, and recapturing individuals

Calculate population size

(number marked) * (number in the second sample/number of marked recaptures)

Dispersion

Spatial distribution within the geographical range

Random dispersion

Neither attracted nor repelled by others of their species

Clumped dispersion

When individuals group together

Uniform dispersion

When individuals repel each other

Age structure

Statistical description of the relative numbers of individuals in each age class

Generation time

Average time between the birth of an organism and that birth of its offspring

Sex ratio

Male-female ratio

Demography

Study of processes that change a population's size and density through time

Life table

Summarizes demographic characteristics of a population

Age-specific mortality

Proportion of individuals alive at the start of an age interval that died during that age interval

Age-specific survivorship

Proportion of individuals alive at the start of an age interval that survived until the start of the next age interval

Age-specific fecundity

Number of offspring produced by surviving females during each age interval

Survivorship curve

Displays the rate of survival for individuals over the species average lifespan

Type 1 survivorship curve

High survivorship until late in life, typically large animals that produce few young and provide extended care

Type 2 survivorship curve

Constant rate of mortality in all age classes

Type 3 survivorship curve

High mortality until late in life, typically smaller animals that reproduce a lot

Energy budget

Total amount of energy that an organism can accumulate and use to fuel its activities

Semelparity

Single reproductive episode