Final Exam Review

Question 1

What is evolution?

Answer 1

A change in allele frequencies in a population over time
Does NOT require a change in species
Does NOT indicate why allele frequencies have changed
Occurs in populations, NOT individuals
Requires genetic variation to act on , which comes from mutations that generate new alleles

Question 2

What are the mechanisms of evolution?

Answer 2

1. Selection (Artificial, Natural, Sexual)- Process by which allele frequencies change due to differential reproduction
2. Genetic Drift
3. Migration- When new individuals enter a population from another population and may bring different alleles
   * *All can cause allele frequencies to change

Question 3

What is heritability (h2) and how is it measured?

Answer 3

Proportion of a population’s phenotypic variation controlled by genetic rather than environmental factors
Slope of regression line between mean parent and offspring values for a trait
H2= VG/VP
VP= VG + VE

Question 4

How do the different forms of selection differ from each other? How are they the same?

Answer 4

All forms of selection share 2 variables:
1) Heritable variation among individuals
2) Differences among individuals in number of surviving offspring
DIFFERENCES
Artificial- Humans choose which individuals pass on alleles; Some alleles become more common because of selective breeding
Natural- Nature decides which individuals reproduce most; Different environments select for different traits depending on major causes of death; Results in ADAPTATIONS; NOT goal-oriented; Can be fast or slow, depends on how much advantage trait provides; Does not create new traits, but eliminates old ones if a better one exists
Sexual- individuals who are better at obtaining mates reproduce more (2 components- female mate choice and male competition)

Question 5

What is fitness?

Answer 5

# of copies of an individual's genes that get passed on to future generations
Good indicator is number of surviving children and grandchildren

Question 6

What are adaptations?

Answer 6

Traits that help an organism survive and reproduce in a particular environment
Favored by selection

Question 7

How do the following provide evidence of evolution: fossils, homology, vestigial
traits, biogeography, the universality of the genetic code, ERVs?

Answer 7

All demonstrate change over time and common ancestry and support each other
Fossils- Mere existence does NOT provide evidence for evolution; but, the fossil record does; Organisms are found in historical sequence; Fossils demonstrate a gradual transition among forms
Homology- Similarities in structure among organisms, as is predicted if they arose from the same common ancestor
Vestigial traits- Structures that have no apparent purpose, but are carry-overs from ancestral species
Biogeography- Observations: Many island species are endemic; endemic species on islands are similar to species on nearest mainland; species found on nearby islands are similar to each other; Best explanation: the island species evolved from populations that were begun by individuals from the mainland; This is the pattern predicted by common ancestry
Universality of genetic code- All living organisms have the same system for building proteins, which is STRONG evidence that all life shares a common ancestor
ERVs- Inactive viral sequences embedded in the genome; Remnants of past infections; Patterns of shared ERVs correspond to hypothesized phylogenies, as would be predicted by common ancestry

Question 8

What is a scientific theory?

Answer 8

A big explanatory idea
Broad-ranging; pulls together diverse observations
Testable; allows predictions about future observations; conforms to laws of chemistry and physics; open to revision

Question 9

What criteria must be met for an explanation to be considered scientific?

Answer 9

1) Be testable
2) Conform to the laws of chemistry and physics (be natural, not supernatural)
Open to revision

Question 10

What is the significance of Hardy-Weinberg Equilibrium?

Answer 10

Dominant alleles do not automatically spread: there needs to be an evolutionary mechanism to cause an allele to spread
We can analyze populations to identify genes that are evolving
There is no evolution in the absence of an evolutionary mechanism
Allele frequencies are inherently stable unless there are pertubations

Question 11

What were the important trends in human evolution?

Answer 11

Human and chimp lineages diverged about 6 mya
Many different hominin species have existed, often simultaneously
Human family tree is a twiggy bush rather than a linear progression
Few older hominin fossils have been found because they died in forests that do not fossilize well and are hard to find fossils in
1st bipeds (walk on 2 legs) appeared early in hominin evolution (advantage= can see farther, keep cooler, carry food, and better for long-distance travel)
1st manufactured stone tools about 2 mya
Fire about .5 mya

Question 12

What is the relationship between humans and chimpanzees?

Answer 12

Humans and chimps share a recent common ancestor that lived about 6 million years ago

Question 13

What are the different forms of symbiosis?

Answer 13

1. Mutualism- a symbiosis in which both organisms benefit (bee and flower)
2. Commensalism- a symbiosis in which one organism benefits without helping or harming the other (Clown fish and anemone)
3. Parasitism- a symbiosis in which one organism benefits at the expense of the other (humans and tapeworms)

Question 14

How do organisms optimize offspring size and number?

Answer 14

Optimizing size vs number of offspring
Larger offspring typically have higher survival, but fewer can be produced
Solution: produce offspring of size that yields the greatest number of survivors
Multiply number by survival probability for each size

Question 15

How are population sizes estimated in the field?

Answer 15

Mark and recapture studies
1. Capture sample of animals and mark them
2. Release marked animals
3. Later date: capture new sample
4. Use the proportion of marked animals that were recaught to estimate total population size
Marked(1)/Pop. size= recaught marked (2)/Total caught (2)

Question 16

What is an age structure diagram and how is it used?

Answer 16

Description of what % of population is of reproductive vs prereproductive age
Generates prediction of how population size will change in the future
Width of segment represents percent of population in that age bracket

Question 17

What is a survivorship curve and what does it tell you about a population?

Answer 17

Represents probability of survival relative to stage of life
1. Convex 2. Constant 3. Concave
% surviving vs. % max lifespan

Question 18

How do we use a life table to determine life expectancies and survivorship curves?

Answer 18

Give a systematic picture of age specific mortality and survival

Question 19

What is intrinsic rate of increase (r)?

Answer 19

Population growth rate for a population with unlimited resources
Larger organisms have smaller Rmax values

Question 20

What is carrying capacity (k)?

Answer 20

The maximum number of individuals that an environment can sustainably support

Question 21

What is environmental resistance?

Answer 21

Factors that limit population growth
Maintain populations at or below carrying capacity
Two categories: density-dependent and density-independent

Question 22

What is the difference between density-dependent and density-independent effects
on population growth?

Answer 22

Dependent- Limit population growth as density increases by decreasing the birth rate and or increasing the death rate; Can cause population to stabilize or decline
Intraspecific competition (within species)-reduces individual growth rate and reproduction
Disease/parasites- spread easily as pop. density increases
Predation- as prey increase, supports larger population of predators
Food, light, space

Independent-
Affect population size regardless of density
ex: Weather

Question 23

What are the trends in human population growth?

Answer 23

Growth rate for humans is 1.1%
Majority in less developed countries
Past increases in human pop. size were associated with increases in carrying capacity
Has been a decline in pop growth RATE since 1960s
Increases in carrying capacity with tool-making and industrial revolutions

Question 24

What is the competitive exclusion principle?

Answer 24

No 2 species can have exactly the same niche
2 species that compete for the same resources cannot steadily coexist.
One species will outcompete the other

Question 25

What is resource partitioning?

Answer 25

How species avoid niche overlap
The use of slightly different niches to minimize competition
Examples: different species of warblers live in different areas of same trees, different root morphologies in plants, finches eat different foods, hawks and owls are active at different times of day, frogs breed at different times of the year

Question 26

How do we interpret the zero-growth isoclines for competing populations?

Answer 26

For analysis of interspecific competition

Mathematical representation of competitive exclusion principle

Question 27

How do predator-prey cycles work?

Answer 27

The 2 populations limit each other’s density
Prey pop limited by predation and predator pop limited by prey availability
Many infectious diseases also follow cycle pattern if the disease can only be contracted once

Question 28

What is coevolution?

Answer 28

2 species evolve together and have specific adaptations for dealing with each other
Like an arms race, because 2 sides go back and forth putting pressure on one another to get better
Can lead to extreme adaptations for both

Question 29

What is genetic drift (incl. bottleneck and founder effects)?

Answer 29

Any change in allele frequencies due to chance, especially important in small populations where alleles are easily lost
Founder effect= a few individuals start a new population, but new population usually only contains a subset of alleles from parent population
Bottleneck effect= a catastrophic event reduces the population to a small size and survivors are unlikely to carry all alleles from original population

Question 30

Why are males usually the competitive sex, and females the choosey sex?

Answer 30

Females need to be choosier because they invest more time and resources to offspring (need to evaluate that male is correct species, has good territory, good parental care, and has good genes for survival) Mating mistakes are more costly for females. Females who are choosier obtain better genes for offspring and leave behind more offspring than females who mate randomly
Males need to be more competitive because the males who mate the most are most likely to pass on genes

Question 31

What are the modes of selection?

Answer 31

Cause traits to change or stay the same

1. Directional selection- favors extreme value of trait and causes shift to one extreme
2. Stabilizing selection- favors intermediate values of trait; mean is unchanged but variance decreases
3. Disruptive selection- favors both extremes of a trait, variance increases, can lead to bimodal distribution of trait over time.

Question 32

What is a species, and what steps are necessary for speciation to occur?

Answer 32

A species is a group of organisms that have the potential to breed with each other and produce live, fertile offspring
1) 2 populations must become reproductively isolated from each other (no cross mating)
2) Genetic differences must build up between the 2 populations as a result of differential selection pressures and/or genetic drift
Once the genetic differences are great enough to prevent reproduction, the 2 groups are considered separate species

Question 33

What is standing genetic variation and how does it influence selection?

Answer 33

It is a large amount of variation in the alleles a population possesses.
If there is a large amount of it, there is no need to wait for new mutations to arise for selection to occur, it can act on the variation already present in the population

Question 34

How is the age of a rock determined using radiometric dating?

Answer 34

Based on decay rate of radioactive isotopes
Radioactive elements are unstable and break down spontaneously over time
All rocks and minerals contain trace amounts of these elements

Question 35

How do we interpret evolutionary trees?

Answer 35

Extent to which 2 species are related is determined by how recently they shared a common ancestor, not by the number of nodes that separate them
Species closer together on tree are not more related

Question 36

How do we determine which possible evolutionary tree is the most parsimonious?

Answer 36

Character state reconstruction- inferring evolutionary history of traits based on their distribution in extant species
Simpler explanations are favored (fewer evolutionary transitions)
Choose a set of traits to compare among species, construct all possible trees, and count how many trait transitions must occur for each tree

Question 37

What is the endosymbiont hypothesis?

Answer 37

Eukaryotes evolved from prokaryotes that engulfed or were invaded by other cells
The engulfed cell lived and reproduced inside the host cell (endosymbiosis) and the 2 cells became co-dependent

Question 38

How are the fish, amphibians, birds, reptiles, and mammals related to each other?

Answer 38

See tree

Question 39

Where did modern humans evolve?

Answer 39

Africa

Question 40

What is the difference between the movement of energy and the movement of nutrients through an ecosystem?

Answer 40

Energy flows in one direction, but nutrients are recycled

Question 41

Why is there a loss of energy as it moves up the food chain?

Answer 41

Most energy consumed by an organism is used for its own metabolism and converted to heat
The only energy available to a trophic level is the energy STORED in the bodies of the level below, which is only a small percentage

Question 42

What are the implications of this loss?

Answer 42

There is a limit to the number of trophic levels possible
The number of individuals decreases as you move up trophic levels
Biomagnification- the accumulation of toxic substances in the higher trophic levels

Question 43

How does biomagnification work?

Answer 43

Chemicals that dissolve in fat remain in the animal that ate it
One predator eats many prey to sustain diet
So, higher concentrations of the chemicals exist in higher trophic levels

Question 44

What are the causes and consequences of the thinning of the ozone layer?

Answer 44

More UV rays enter atmosphere, creating chlorine atoms and warming atmosphere

Question 45

What are the causes and consequences of climate change?

Answer 45

Causes: sun radiation reaching early. Greenhouse gas increases, CO2
Consequences: water expands, rising sea levels, droughts, extinction, changing weather patterns

Question 46

How do greenhouse gases cause the greenhouse effect?

Answer 46

The atmosphere acts like a blanket, trapping heat and thereby raising surface temperatures. This is the greenhouse effect, which makes life possible here on Earth. The key to the greenhouse effect lies in the difference in wavelength between incoming and outgoing radiation. Hot objects radiate more energy than cool ones, and they also radiate at shorter wavelengths. Because the Sun is hot, it radiates mostly at short wavelengths. In contrast, Earth is much cooler and thus radiates at longer wavelengths.13

Question 47

How does climate change reflect an imbalance in the carbon cycle?

Answer 47

CO2 is a greenhouse gas that is released when fossil fuels are burned, so there are excess amounts of it

Question 48

Why do most climate scientists attribute climate change to human activity?

Answer 48

Since the 1850s, concentrations of CO2 and other greenhouse gases have increased markedly, primary from fossil fuel combustion.