Evolution Test Vocab

Natural Selection

The process by which individuals with traits better suited to their environment survive and reproduce to pass on those advantageous traits to their offspring (Charles Darwin) - Survival of the fittest

Process of Natural Selection(4)

Inheritable variation exists in a population

There is competition, or a struggle for survival - # of offspring exceeds what ENV can support

Selection - different environmental pressures exist

Individuals with the right adaptations(beneficial traits) will more likely survive, reproduce, pass on their genes.

Evolution

Occurs when allele frequency of population changes over time

Mutation

Changes in DNA sequences

Mutations, or changes in DNA sequences…(2)

Create new alleles for natural selection to act on (2)

• are the only way new alleles can be generated

• produce genetic variations in populations

They can be…(2)

• beneficial - creates successful variation of existing trait

• harmful - decrease survival or reproduction

• neutral - no immediate effect

Sexual Reproduction

Reproduction involving meiosis and fertilization

Sexual Reproduction(2):

Creates new allele combinations

Increases genetic diversity without producing new alleles.

Different ways of creating diversity(3)

Crossing over

independent assortment

random fertilization

Crossing Over (2)

exchange of non-sister chromatid segments between homologous CHR during prophase I

produces recombinants, offspring that have different gene combinations than parents

Independent Assortment

Homologous CHR line up randomly and independently from one another during metaphase I.

• 2²³ possible gametes in humans.

Random Fertilization

Any sperm can fertilize any egg.

Overproduction of offspring(2)

Species produce more offspring that ENV. can support

• ultimately, population > resources

• produces competition for resources

  • Resources like food, space, and mates determine carrying capacity.

Allows survival of the fittest

carrying capacity

maximum population that the environment can support

Survival of the fittest

Individuals with advantageous traits (better at getting resources) are more likely to survive and reproduce

• such traits will become more common over time

Selective Pressures(abiotic)

Environmental factors that affect an organism’s chances of survival and reproduction

• may changes over time, altering which adaptations are beneficial for survival

abiotic factors can be(2)

positive - favor individuals with certain traits to survive and reproduce

negative - reduce the number of individuals less suited

Density Independent Factors

factors that impact a population regardless of its size

Examples of Density Independent Factors(3)

high temperatures - heatwave (coral bleaching)

low temperatures - sudden frost can kill plants, or other food sources

droughts, floods, and storms can also impact populations

Adaptations

Variations among individuals

• organisms have different adaptations that allow them to be better suited to their ENV.

Intraspecific Competition and Survival

organisms with better adaptations will more likely surive in competition for the same resources

• those with higher fitness will pass on their genes to the next generation.

• fitness is relative, or depends on ENV

This is how natural selection changes population traits over time

Fitness

Organism’s ability to survive and reproduce

Heritability of Traits: Evolution

Change in heritable traits of a population over time, occurs via natural selection

Heritable traits

traits encoded by DNA(genes) and passed from parent to offspring

• only changes in DNA like mutations can be inherited

acquired characteristics are not inherited

• those gained in life (muscle, loss of limb) do not change DNA, and cannot be passed to offpsring

• Environmental factors (diet, sunlight, injury) can only impact the individual not their genes.

Lamarck’s theory is incorrect

Sexual Selection(3)

Type of natural selection where certain traits increase an organism’s ability to attract a mate and reproduce.

• such traits aren’t directly tied to survival

  • Act as signals of fitness(health, strength, and good genes)

• sexual selection can produce significant differences between males and females, known as sexual dimorphism

Types of sexual selection: Intersexual Selection

Individuals of one sex (usually females) choose mates based on traits (color, dance, song)

Examples of Intersexual Selection(2)

Bird of Paradise: Males have bright plumage and complex dances that attract females, even though they may increase predation risk

Deer: Males grow large antlers, despite being energetically costly to grow and maintain

Natural Selection Experiments

Guppies are a species of fish that evolve traits as a consequence of both natural selection and sexual selection

• John Endler placed guppies into artificial stream tanks with gravel of different colors.

  • independent variables were presence of predators(high, low, none) and color of gravel (for camouflage)

Results of Endler

Guppies with predators evolved duller colors for camouflage

• favored by natural selection (survival)

guppies without predators evolved brighter colors due to female preference

• favored by sexual selection (mating)

Gene Pool

Total number of alleles for all genes in a population (same species in same area, interbreeding) at a given time

Effect of gene pool size on populations

• large ones increase genetic diversity, fitness, and survival

• smaller ones increase chances of extinction

  • evolution occurs when allele frequencies in the gene pool change over time.

Allele Frequencies of Isolated Populations: Genetic Drift

Change in gene pool due to chance or random events

• especially in isolated populations

  • larger populations maintain stability due to greater total number of alleles

Examples of Genetic Drift(2)

Bottleneck effect

Founder Effect

Bottleneck Effect

event that reduces a population size by more than 50%

• natural disasters(fire, flood) or humans (overfishing)

Founder effect

small group leaves its original population to setup a new one

• differs from bottlenecks, original population stays intact

Both populations will have less genetic variability

• be more prone to genetic drifts

Neo-Darwinism: Allele Frequency

Prevalence of an allele, in comparison to others in the gene pool, represented as a percentage (0-1.0)

How allele frequency is evidence of evolution via natural selection

As favorable traits are passed on, the frequency of advantageous alleles increases.

• alleles for less favorable traits decrease in frequency

Creation of Neo-Darwinism

Darwin proposed evolution by natural selection based on observation, unaware of genes.

• modern biologists combined natural selection with genes.

Neo-Darwinism

Evolution as changes in allele frequencies caused by natural selection acting on heritable genetic variation.

Types of Selection(3)

All 3 types result in a change in allele frequency

• Stabilizing Selection

• Directional Selection

• Disruptive Selection

Stabilizing Selection

Favors intermediate phenotype and selects over the two extremes

• traits become more uniform around the average

  • ex. human birth weight

Directional Selection

Favors one extreme phenotype over the other

• trait distribution shifts in one direction

  • ex. peppered moths, antibiotic resistance in bacteria

Disruptive Selection

Favors both extreme phenotypes over the immediate

• trait distribution splits into 2 distinct groups

  • may eventually encourage speciation

    • ex. beak size

Conditions for Genetic Equilibrium(5) pgmms

to maintain genetic equilibrium(keep allele frequencies the same), the following five conditions must be met:

Large population size - smaller size, greater likelihood that small changes produce significant effects (genetic drift)

No gene flow - no individuals moving in/out of populations via migration

no mutations - no new alleles introduced

random mating - individuals mate without preference for traits

no natural selection - all genotypes must have equal chances or survival and reproduction

Artificial Selection

Process where humans choose individuals with desriable traits to reproduce

• purpose: enhance specific traits over generations

Examples of Artificial Selection

Crop Plants - select for plants with larger fruits or pest resistance

Domesticated animals - breeding dogs for size, temperament, or coat type

Antibiotic Resistance

Bacteria have evolved resistance through natural selection, as an unintended consequence of human action

Bacteria become antibiotic resistant through mutation

When exposed to antibiotics (selective pressure), regular bacteria will die

Those with resistance will survive and reproduce

• will flourish due to a lack of competition

They will further spread resistance by transferring R plasmids via bacterial conjugation

• This adaptation has increased the allele frequency of the population

Lamarckism

Evolution via acquired traits

ex. trees growing asymmetrically due to wind

Sequential Evidence

Evolution is heritable, therefore change is visible in(3) DNA, RNA, AA

Sequence Comparison of Genes

fewer differences in more closely related species

Sequence differences in genes

can be accounted for by splitting ancestral species

Gene families like Hox Gene

Hox Gene

Determines body plan during development

found in all ORG with a clear head-to-tail axis

Selective Breeding