chapter 18 and 19 biology full set

adaptive evolution

increase in frequency of beneficial alleles and decrease in deleterious alleles due to selection

allele frequency

(also, gene frequency) rate at which a specific allele appears within a population

assortative mating

when individuals tend to mate with those who are phenotypically similar to themselves

bottleneck effect

magnification of genetic drift as a result of natural events or catastrophes

cline

gradual geographic variation across an ecological gradient

directional selection

selection that favors phenotypes at one end of the spectrum of existing variation

diversifying selection

selection that favors two or more distinct phenotypes

evolutionary fitness

(also, Darwinian fitness) individual's ability to survive and reproduce

founder effect

event that initiates an allele frequency change in part of the population, which is not typical of the original population

frequency-dependent selection

selection that favors phenotypes that are either common (positive frequency-dependent selection) or rare (negative frequency-dependent selection)

gene flow

flow of alleles in and out of a population due to the migration of individuals or gametes

gene pool

all of the alleles carried by all of the individuals in the population

genetic drift

effect of chance on a population's gene pool

genetic structure

distribution of the different possible genotypes in a population

genetic variance

diversity of alleles and genotypes in a population

geographical variation

differences in the phenotypic variation between populations that are separated geographically

good genes hypothesis

theory of sexual selection that argues individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease

handicap principle

theory of sexual selection that argues only the fittest individuals can afford costly traits

heritability

fraction of population variation that can be attributed to its genetic variance

honest signal

trait that gives a truthful impression of an individual's fitness

inbreeding

mating of closely related individuals

inbreeding depression

increase in abnormalities and disease in inbreeding populations

macroevolution

broader scale evolutionary changes seen over paleontological time

microevolution

changes in a population's genetic structure

modern synthesis

overarching evolutionary paradigm that took shape by the 1940s and is generally accepted today

nonrandom mating

changes in a population's gene pool due to mate choice or other forces that cause individuals to mate with certain phenotypes more than others

population genetics

study of how selective forces change the allele frequencies in a population over time

population variation

distribution of phenotypes in a population

relative fitness

individual's ability to survive and reproduce relative to the rest of the population

selective pressure

environmental factor that causes one phenotype to be better than another

sexual dimorphism

phenotypic difference between the males and females of a population

stabilizing selection

selection that favors average phenotypes

19.1 Population Evolution

The modern synthesis of evolutionary theory grew out of the cohesion of Darwin's, Wallace's, and Mendel's thoughts on evolution and heredity, along with the more modern study of population genetics. It describes the evolution of populations and species, from small-scale changes among individuals to large-scale changes over paleontological time periods. To understand how organisms evolve, scientists can track populations' allele frequencies over time. If they differ from generation to generation, scientists can conclude that the population is not in Hardy-Weinberg equilibrium, and is thus evolving.

19.2 Population Genetics

Both genetic and environmental factors can cause phenotypic variation in a population. Different alleles

can confer different phenotypes, and different environments can also cause individuals to look or act

differently. Only those differences encoded in an individual's genes, however, can be passed to its

offspring and, thus, be a target of natural selection. Natural selection works by selecting for alleles that

confer beneficial traits or behaviors, while selecting against those for deleterious qualities. Genetic drift

stems from the chance occurrence that some individuals in the germ line have more offspring than

others. When individuals leave or join the population, allele frequencies can change as a result of gene

flow. Mutations to an individual's DNA may introduce new variation into a population. Allele frequencies can also be altered when individuals do not randomly mate with others in the group.

19.3 Adaptive Evolution

Because natural selection acts to increase the frequency of beneficial alleles and traits while decreasing the frequency of deleterious qualities, it is adaptive evolution. Natural selection acts at the level of the individual, selecting for those that have a higher overall fitness compared to the rest of the population.

If the fit phenotypes are those that are similar, natural selection will result in stabilizing selection, and an overall decrease in the population's variation. Directional selection works to shift a population's

variance toward a new, fit phenotype, as environmental conditions change. In contrast, diversifying selection results in increased genetic variance by selecting for two or more distinct phenotypes. Other types of selection include frequency-dependent selection, in which individuals with either common (positive frequency-dependent selection) or rare (negative frequency-dependent selection) are selected for. Finally, sexual selection results from the fact that one sex has more variance in the reproductive success than the other. As a result, males and females experience different selective pressures, which can often lead to the evolution of phenotypic differences, or sexual dimorphisms, between the two.

adaptation

heritable trait or behavior in an organism that aids in its survival and reproduction in its present environment

adaptive radiation

speciation when one species radiates out to form several other species

allopatric speciation

speciation that occurs via geographic separation

allopolyploid

polyploidy formed between two related, but separate species

aneuploidy

condition of a cell having an extra chromosome or missing a chromosome for its species

autopolyploid

polyploidy formed within a single species

behavioral isolation

type of reproductive isolation that occurs when a specific behavior or lack of one prevents reproduction from taking place

convergent evolution

process by which groups of organisms independently evolve to similar forms

dispersal

allopatric speciation that occurs when a few members of a species move to a new geographical area

divergent evolution

process by which groups of organisms evolve in diverse directions from a common point

gametic barrier

prezygotic barrier occurring when closely related individuals of different species mate, but differences in their gamete cells (eggs and sperm) prevent fertilization from taking place

gradual speciation model

model that shows how species diverge gradually over time in small steps

habitat isolation

reproductive isolation resulting when populations of a species move or are moved to a new habitat, taking up residence in a place that no longer overlaps with the other populations of the same species

homologous structures

parallel structures in diverse organisms that have a common ancestor

hybrid

offspring of two closely related individuals, not of the same species

hybrid zone

area where two closely related species continue to interact and reproduce, forming hybrids

natural selection

reproduction of individuals with favorable genetic traits that survive environmental change because of those traits, leading to evolutionary change

postzygotic barrier

reproductive isolation mechanism that occurs after zygote formation

prezygotic barrier

reproductive isolation mechanism that occurs before zygote formation

reinforcement

continued speciation divergence between two related species due to low fitness of hybrids between them

reproductive isolation

situation that occurs when a species is reproductively independent from other species; this may be brought about by behavior, location, or reproductive barriers

speciation

formation of a new species

species

group of populations that interbreed and produce fertile offspring

punctuated equilibrium

model for rapid speciation that can occur when an event causes a small portion of a population to be cut off from the rest of the population

sympatric speciation

speciation that occurs in the same geographic space

temporal isolation

differences in breeding schedules that can act as a form of prezygotic barrier leading to reproductive isolation

variation

genetic differences among individuals in a population

vestigial structure

physical structure present in an organism but that has no apparent function and appears to be from a functional structure in a distant ancestor

vicariance

allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups

18.1 Understanding Evolution

Evolution is the process of adaptation through mutation which allows more desirable characteristics to

be passed to the next generation. Over time, organisms evolve more characteristics that are beneficial to

their survival. For living organisms to adapt and change to environmental pressures, genetic variation

must be present. With genetic variation, individuals have differences in form and function that allow

some to survive certain conditions better than others. These organisms pass their favorable traits to their

offspring. Eventually, environments change, and what was once a desirable, advantageous trait may

become an undesirable trait and organisms may further evolve. Evolution may be convergent with

similar traits evolving in multiple species or divergent with diverse traits evolving in multiple species

that came from a common ancestor. Evidence of evolution can be observed by means of DNA code and

the fossil record, and also by the existence of homologous and vestigial structures.

18.2 Formation of New Species

Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through

mechanisms that occur within a shared habitat (sympatric speciation). Both pathways isolate a

population reproductively in some form. Mechanisms of reproductive isolation act as barriers between

closely related species, enabling them to diverge and exist as genetically independent species.

Prezygotic barriers block reproduction prior to formation of a zygote, whereas postzygotic barriers

block reproduction after fertilization occurs. For a new species to develop, something must cause a

breach in the reproductive barriers. Sympatric speciation can occur through errors in meiosis that form gametes with extra chromosomes (polyploidy). Autopolyploidy occurs within a single species, whereas

allopolyploidy occurs between closely related species.

18.3 Reconnection and Rates of Speciation

Speciation is not a precise division: overlap between closely related species can occur in areas called

hybrid zones. Organisms reproduce with other similar organisms. The fitness of these hybrid offspring

can affect the evolutionary path of the two species. Scientists propose two models for the rate of

speciation: one model illustrates how a species can change slowly over time; the other model

demonstrates how change can occur quickly from a parent generation to a new species. Both models

continue to follow the patterns of natural selection.

evolution is considered to be what theory>?

unifying theory of biology

what is the theory of evolution?

1.The theory of evolution by natural selection explains both the unity and diversity of life

2.Unity: all life evolved from a common ancestor and all life has the same "raw materials to work with. Thus, similarities are to be expected.

3.Diversity: all life has evolve to survive in different environments and fill different ecological roles

who is Charles Darwin? what did he work with? what were his most important observations? what was one of his most famous work?

1.Charles Darwin

Well-educated thanks to his parents, who intended for him to become a doctor or clergyman, but he chose a different path...naturalist! Took a job at the age of 22 on the HMS Beagle, a survey ship preparing for a long expedition to the South American coast.

2.Collected thousands of fossils and living specimens of plants and animals while keeping detailed notes.

3.Made the important observation that animals that lived geographically close to each other were more similar than animals that live far apart in similar climates...

4Some of his most important work was done in the Galapagos islands....

the Galapagos location.

1. The Galapagos are relatively young volcanic islands located ~540 miles off the coast of South America

Why are Darwin observations in the Galapagos are endemic to the islands?

Because they're not found ANYWHERE else. They are similar to south American species

Darwin and "descent with modifications"- what is this

1. When Darwin returned to England 5 years later, had concluded that present-day species are descended from ancient ancestors that they may still resemble.

2.Over time, he believed the differences accumulated by a process he called "descent with modification" (what we now know as evolution!)

was Darwin the first to propose the concept of evolution?

no, but he was the first to provide a scientific explanation..... and introduced the concept of natural selection.

As descendents of a remote ancestor spread into various habitats over millions of years, they accumulated adaptations to help them survive in their environment

Two assertions on Darwin

1. Living species are the descendents of ancestral species that were different from present-day species

2.Natural selection is the mechanism for evolutionary change

where can fossils ne produced?

1.bones and teeth can remain as fossils

2.cast of the original animal

3.Dead organism is captured in sediment

4.Organic components decompose

5.Space filled by minerals dissolved in water

6. imprint left behind like a footprint or burrow.

How can you figure out the age of a fossil?

Fossils can be aged by determining the age of the surrounding rock layer (stratum)

what can fossils provide us with?

evidence of transitional forms linking very different types of animals

Darwin linked what mammals together?

whales evolved from land-dwelling mammals

Pakicetus

a four-legged mammal but had cetacean ear structures, 50myo

Ambulocetus and Rodhocetus

had short sturdy legs for mobility on land but also a powerful tail and paddle-like hind feet for swimming, plus cetacean ear structures, 48myo

Dorudon

transitioned to fully aquatic life

What is homology

similarities resulting from common ancestry.

What is a homologous structure?

features that are similar in structure but appear in different organisms and have different functions

One homology Darwin pointed out was humans, cats, whales, and bats all have what uncommon????? why is this?

1.Similarity among vertebrate forelimbs

2. His hypothesis was that they all came from a common ancestor but had become adapted to different functions over time.

what us vestigial structure

structure that is unused and apparently without function. They appear to be leftovers.

EX: wings in flightless birds, leg bones in whales and larges snakes, eyes striation in blind fish and salamanders, the coccyx and pilomotor reflex in humans

What do unrelated organism share in similar living environments? Why? EX?

1.certain characteristics

2.This occurs in response to the organisms being exposed to similar selection pressures!

Example: White animals in the Arctic

The more sequence difference between species means what?

the more distant their last common ancestor is

What is a family tree used to show? what is the scientific name?

-how related different species are to one another.

-We call these "phylogenetic trees"

What is artificial selection?

selective breeding of plants and animals

What two things was artificial selection dependent on over time?

1.Variation - breeder selects the individual with the most desired version of the trait

2.Heritability - trait must be able to be passed on to offspring

Darwin determine how NATURE could play the role of the breeder by preferentially "selecting" one version of a trait over another. what were 3 things he came up with?

1. Determined that offspring that are better adapted to their environment (i.e. better able to obtain food and resources) would be more likely to survive to reproduce.

2. Only organisms that reproduce can pass on their traits.

3. Then these traits become more common in the population.

what evolves?

individuals do not evolve...... POPULATIONS EVOLVE

what can natural selection act on?? What does that mean?

1.heritable traits

2.Traits acquired during your lifetime may confer an advantage but those advantages can't be passed on and won't change in frequency in the population

TRUE or FALSE: Evolution is not goal-directed and does not produced "perfect" organisms

true

b/c u A trait that is favored in one situation may be detrimental in another so we often see "compromises" in evolution

Evolution is not intentional it occurs because........

1.Variability exists in a population and it is acted on by environmental pressures

2. If the environment changes, the selection pressures also change

3. Organisms best adapted to their current environment will survive and reproduce, passing on their traits

Examples of evolution in Action

the finches of Galapagos and pestle resistance in insects

The finches of the Galapagos - summary

1. Darwin observed differences in the beaks of finches here when he visited and noted a correlation with food source

2.Studied since 1976 by Peter and Rosemary Grant

3.These birds prefer small seeds but in dry years, they can be scarce

4. During dry periods, when small seeds are rare and the only food source is large, hard seeds, the average beak size in finch populations tends to increase

5.During wet years, when small seeds are abundant but large, hard seeds are more rare, beak size tends to decrease

pesticide resistance in insects

1.Applying pesticide will initially kill most target insects

2.The ones that survive are resistant to the pesticide

3.They reproduce and now their offspring are also resistant

4.Each generation, the proportion of individuals that are resistant to that pesticide increases.

5.This can also happen with antibiotic medications!

what is Biological species

a group of populations whose members can interbreed and produce fertile offspring