Evolution

Question 1

Define:

Evolution

Answer 1

The change in frequency of a population’s inherited traits over subsequent generations.

Evolution only occurs within populations; individual organisms do not change genetically over time to adjust to their environment.

Question 2

What is the difference between microevolution and macroevolution?

Answer 2

• Microevolution relates to evolutionary changes that occur within a single population. Its scope is fairly small, since it only deals with one species at a time.
• Macroevolution relates to larger-scale changes and interactions between multiple populations (and thus multiple species).

Question 3

Jean-Baptiste Lamarck, a French naturalist, proposed two key ideas as part of his explanation for evolution. Name these ideas.

Answer 3

• Use and disuse
• Inheritance of acquired characteristics

Use and disuse is the idea that we “build up” body parts that we use often, while those parts that we do not use tend to atrophy (weaken). This idea is still considered to be accurate today.

In contrast, inheritance of acquired characteristics (or the thought that organisms pass down traits gained over their lifetimes) is now considered to be wrong.

Question 4

In his famous theory, Jean-Baptiste Lamarck proposed that the “use or disuse” of a trait dictated its heritability. In a classic example, giraffes who often stretched their necks would have offspring with longer necks than average. Describe the problem with this hypothesis.

Answer 4

Non-genetic traits that are acquired during an organism’s lifetime cannot be passed down to its offspring.

According to the “use and disuse” concept, organisms lose traits they do not need and develop traits that are useful to them. However, genes (not acquired traits) are inherited by offspring, making Lamarck’s theory an incorrect, and now discredited, explanation for evolution.

Question 5

Our modern understanding of evolution stems largely from the findings of which individual, who proposed the concept of natural selection?

Answer 5

Charles Darwin

Charles Darwin was a naturalist whose most famous work, On the Origin of Species, proposed the concepts that we understand to be largely true today - most notably, that natural selection drives evolutionary changes within a species as well as the development of new species.

Question 6

Define:

Natural selection

Answer 6

The change in frequency of a trait within a population, based on the effect that trait has on reproductive success.

Traits that allow an organism to produce more viable offspring are more likely to be passed on to future generations.

Question 7

Name five sources or fields of study that provide support for the concept of evolution.

Answer 7

• The study of the fossil record (paleontology)
• The study of the distribution of animals and plants (biogeography)
• Comparative anatomy
• Comparative embryology
• Molecular biology

Question 8

Comparative anatomy most notably includes the study of which two types of anatomical structures?

Answer 8

1. Homologous structures
2. Analogous structures

Question 9

Define:

Homologous structures

Answer 9

These are anatomical features of two species that developed from the same part of a common ancestor.

Species that possess homologous structures must be related. However, the modern versions of these structures do not have to be used for the same purpose.

Question 10

Define:

Analogous structures

Answer 10

These are anatomical structures of two species that share a form or function, but did not develop from a common ancestor.

Species that possess analogous structures must be relatively unrelated. However, since their structures are similar in appearance or function, they may be mistaken for related species.

Question 11

As mammals, both humans and whales developed from a common ancestor. What term describes the relationship between a human arm and a whale fin?

Answer 11

homologous structures

Though used for very different purposes, the appendages are evolutionarily related; both derived from a similar structure in a common ancestor.

Question 12

Birds and insects evolved independently from very different ancestors. What term describes the relationship between a bird wing and a bee wing?

Answer 12

analogous structures

Since both structures serve a similar purpose, it can be tempting to think that they are related. However, since they developed independently from features of different ancestors, they are analogous.

Question 13

What benefit does a vestigial structure give a modern organism?

Answer 13

They provide little to no benefit to the organisms who possess them.

While these features were likely useful to ancestral organisms, they have evolved to lose most or all of their function.

Question 14

Evolutionary biologists would classify the human appendix as which kind of structure?

Answer 14

vestigial

The appendix, an outcropping of the large intestine, has long been thought to provide no function to modern humans. Though recent research has challenged this idea, for the AP Biology exam, continue to remember the appendix as a classic example of a vestigial structure.

Question 15

What is the difference between ontogeny and phylogeny?

Answer 15

• Ontogeny refers to the development of an individual organism throughout its life.
• Phylogeny describes the evolutionary history of a species or other set of organisms.

For example, human ontogeny relates to the transition from zygote to embryo to fetus, then adult. Human phylogeny deals with the descent of modern humans from early ancestors.

Question 16

Is the development of a fertilized egg into an adult chicken an example of ontogeny or phylogeny?

Answer 16

ontogeny

Ontogeny refers to an organism’s development over its lifetime, while phylogeny refers to a species’s development over evolutionary time.

Question 17

What qualities are exhibited by an organism with high fitness?

Answer 17

Organisms with high fitness are those that successfully produce a relatively large number of offspring.

In general, fitness refers to the likelihood that an animal will pass down its genetic material.

On the AP Biology exam, remember that fitness is determined by reproductive success alone. A stronger, more physically capable animal that cannot reproduce is less fit than a weaker animal that can reproduce.

Question 18

Which of the following is the least evolutionarily fit?

• A fish with underdeveloped fins
• A fish without functioning sex organs
• A fish without functioning eyes

Answer 18

The fish that lacks functional sex organs.

Evolutionary fitness refers only to the ability to pass on genetic material. The other two fish certainly may have difficulty surviving, but they can still reproduce.

Question 19

Members of a population who possess beneficial traits survive long enough to produce offspring, while members with harmful traits often die before reaching sexual maturity. Which evolutionary term describes this tendency?

Answer 19

differential reproduction

This concept is a key component of natural selection. Through this mechanism, traits that affect survival are inherited differently, regardless of whether they directly relate to reproduction.

Question 20

What term refers to the set of all genes present in a population?

Answer 20

gene pool

A diverse gene pool allows a species to more easily adapt to changes in its environment. This quality is referred to as genetic variation.

Question 21

Define:

Genetic leakage

Answer 21

The gene flow from one species to the gene pool of another.

Question 22

What genetic value changes within a population as evolution occurs?

Answer 22

allele frequency

Alleles are different forms of genes, and evolution is a change in the frequency of genetic material. Thus, evolution causes some alleles to become more prevalent while others become more rare.

Question 23

What measurement determines the evolutionary success of an allele?

Answer 23

Evolutionary success is determined by the percent representation of an allele in the following generation.

If an allele becomes more prevalent in the gene pool, it is considered evolutionarily successful. However, factors other than natural selection can affect allele frequencies.

Question 24

Which of the following must increase in future generations for an allele to be evolutionarily successful?

• Its phenotypic ratio
• Its genotypic ratio
• Both its phenotypic ratio and its genotypic ratio

Answer 24

Genotypic ratio must increase.

Technically, evolutionary success of an allele refers only to an increase in its frequency in the gene pool. Allele frequencies cannot change without altering genotype frequencies. Note that phenotype frequencies are likely to change as well, but this is not a necessary measure of success.

Question 25

Name three events or mechanisms that increase a population’s genetic diversity.

Answer 25

Many mechanisms serve to increase genetic diversity. Three of the most prevalent are:

• Mutation
• Migration between populations
• Sexual reproduction, especially homologous recombination (crossing over)

Question 26

What condition must be met for a group of individuals to be considered part of the same species?

Answer 26

They must be able to breed and produce viable, fertile offspring.

A species is the most specific category in which an organism can be classified.

Question 27

Horses and donkeys can mate and produce healthy offspring called mules. Why are horses and donkeys considered separate species?

Answer 27

Mules are sterile.

Within a species, the offspring of a breeding pair must be fertile as well as viable. Since mules cannot produce offspring, this condition is not met.

Question 28

Define:

Speciation

Answer 28

The development of new species through evolution.

Generally, speciation occurs when groups of a single species undergo divergent evolution.

Question 29

What is the difference between allopatric and sympatric speciation?

Answer 29

• Allopatric speciation occurs when populations of the same species become physically isolated, usually by a geographical barrier. Over time, the populations evolve to become separate species.
• Sympatric speciation refers to the formation of new species without a geographical barrier. This form of speciation can occur in cases of polyploidy in plants, where some members of a population develop an extra set of chromosomes and can no longer mate with the non-polyploid organisms. Gradually, the polyploid and non-polyploid plants separate into distinct species.

Question 30

What is the difference between adaptation and specialization?

Answer 30

• Adaptation is the process of evolving a trait, through natural selection, that allows a species to better survive in its environment.
• Specialization is a type of adaptation in which a species evolves to fill a specific niche.

Question 31

Viceroy butterflies mimic the appearance of monarch butterflies to repel predators. Is the evolution of this trait an example of adaptation or specialization?

Answer 31

adaptation

Through natural selection, this mimicry has evolved to increase survival. However, sharing the appearance of monarch butterflies does not fill a unique niche.

Question 32

Define:

Ecological niche

Answer 32

The way a specie responds to the environment it lives in, usually by filling a unique role.

A species’ niche can include its method of obtaining resources, its competitive advantages, or its relationship with predators.

Question 33

What will occur between two different species of ant that occupy the same niche?

Answer 33

They will compete with each other for resources, such as food, water, and space.

Competition occurs because resources exist in a finite amount in a given environment. In the long term, a species can avoid competition by adapting to fill a different niche.

Question 34

How does intraspecies competition affect population growth?

Answer 34

Population growth slows in response to competition.

Members of the same species fill the same niche, so they compete with each other for resources. When resources are scarce, the environment cannot support more members of the population and growth is limited.

Question 35

Define:

Inbreeding

Answer 35

The production of offspring from the mating of closely related individuals.

Human examples of inbreeding include some royal families in which cousins married each other for many generations.

Question 36

Define:

Outbreeding

Answer 36

The introduction of new genetic material through mating with unrelated individuals.

Many purebred species, such as dogs and cattle, have developed predispositions for genetic diseases as a result of inbreeding. When the diversity of the gene pool is increased, offspring are more likely to be healthy.

Question 37

A small group of people from Indiana decide to start a new society on a deserted island. Several rare genetic diseases happen to be over-represented in this group, so their offspring display high frequencies of these diseases as well, as do their offspring. This best relates to what phenomenon?

Answer 37

The founder effect

This phenomenon is a form of genetic drift in which a small group of individuals breaks off from a larger population. Alleles that happen to be prevalent in this group will now be displayed much more frequently in future generations than would be expected in the original, larger population.

Question 38

What term describes a major reduction in the number of individuals in a population?

Answer 38

bottleneck

Bottlenecks are generally caused by catastrophic events, whether environmental (such as a natural disaster) or human-related.

Question 39

At one point, overhunting caused the American bison population to drop to fewer than 1000 individuals. What term describes this situation?

Answer 39

bottleneck

Bottlenecks can dramatically change the gene pool, since all subsequent members of the species descend from a small number of individuals.

Question 40

What is genetic drift?

Answer 40

This describes changes in allele frequencies that result from random events.

Often, genetic drift involves situations where part of the population experiences some disaster or becomes isolated from the rest. For example, consider a rat population where allele freqencies for coat color are fairly even. If a flood happens to kill most of the white rats, the resulting decrease in the “white” allele is a result of genetic drift.

Question 41

What kind of factors promote genetic drift?

Answer 41

Genetic drift is promoted by random chance. It relates to changes in allele frequency that occur separately from natural selection.

One example is a bottleneck, or a sharp reduction in population size. The gene pool of the individuals who happen to survive will then determine the characteristics of their offspring, regardless of whether these traits are favorable.

Question 42

What occurs when two groups undergo divergent evolution?

Answer 42

It causes related groups to become increasingly different. In other words, they evolve apart.

Over time, divergent evolution can lead to speciation, when groups differ to the point of being unable to interbreed.

Question 43

What occurs when two groups undergo parallel evolution?

Answer 43

It causes distinct lineages to evolve similar traits over time.

This differs from convergent evolution, in which two lineages become increasingly more similar to each other. In contrast, parallel evolution involves the independent development of like traits in organisms without an increase in overall resemblance.

Question 44

What occurs when two groups undergo convergent evolution?

Answer 44

It causes unrelated, originally dissimilar groups to become increasingly similar.

This often occurs when two species begin to fill the same ecological niche.

Question 45

What type of evolution is demonstrated by bats and owls?

Answer 45

convergent evolution

While both possess the ability to fly, bats are mammals while birds are avian species. Their anatomical structures did not come from a common ancestor, but developed separately and became more similar over time.

Question 46

Which type of evolution can result in the existence of homologous structures?

Answer 46

divergent evolution

By definition, homologous structures must have developed from a common ancestor. Thus, species with these structures are the eventual result of divergence from that ancestor.

Question 47

Which type of evolution can result in the existence of analogous structures?

Answer 47

convergent evolution

When two unrelated species converge, they often evolve features with similar appearances or functions. Since these structures did not develop from a common ancestor, they are analogous.

Question 48

Name the three types of natural selection.

Answer 48

1. directional selection
2. stabilizing selection
3. disruptive selection

Question 49

Which type of natural selection is shown in the image below?

Answer 49

stabilizing selection

Stabilizing selection occurs when extreme phenotypes confer a disadvantage to an organism’s fitness. Over time, the frequency of moderate phenotypes will increase.

Question 50

Which type of natural selection is shown in the image below?

Answer 50

disruptive selection

Disruptive selection occurs when extreme traits are advantageous while moderate traits are not. As a result, the frequencies of the extreme phenotypes increase over time.

Question 51

Which type of natural selection is shown in the image below?

Answer 51

directional selection

Directional selection occurs when a single extreme trait provides a survival advantage. Over time, the frequency of individuals with that trait will rise.

Question 52

Which type of selection helps determine human birthweight?

Answer 52

stabilizing selection

A baby born too small would have difficulty surviving on its own, but an abnormally large baby would be hard for the mother to deliver. Since birthweight is kept within a moderate range, it exemplifies stabilizing selection.

Question 53

A population of horses consists of many individuals with very long manes and many with short manes, but few in the middle. This is likely the result of which form of natural selection?

Answer 53

disruptive selection

Disruptive selection favors extreme variations of a trait over more moderate ones. A classic example is the London peppered moth, where black wings were easily camouflaged in industrial surroundings and white wings blended in within rural areas. Gray moths, which could be seen by predators in both areas, became less prevalent over time.

Question 54

Which type of selection best relates to antibiotic-resistant bacteria?

Answer 54

directional selection

Before selection, a bacterial colony contains members with varying degrees of resistance. After exposure to an antibiotic, only those individuals with high resistance remain, and they can propagate to form a new, resistant colony.

Question 55

Define:

Group selection

Answer 55

Itrefers to genetic changes that occur over time due to the fitness of a group rather than an individual.

Group selection has been used to explain altruism, or selfless behavior. Though it remains controversial among evolutionary biologists, this topic could certainly be mentioned on the AP Biology exam.

Question 56

What term is often used to connect group selection to altruistic behavior?

Answer 56

Kin selection, or the evolutionary preference for behaviors that benefit relatives, is often used to explain altruism.

Not all species exhibit altruistic behavior. Within those that do, “selfless” actions that can harm an individual often benefit the surrounding members of the population. This indirectly passes on the genes of that individual by promoting the survival and reproduction of family members.

Question 57

With regard to evolution, what is an isolating mechanism?

Answer 57

A feature that prevents two species from mating or producing fertile offspring. Such features prevent distinct species from combining.

Isolating mechanisms can be either prezygotic or postzygotic.

Question 58

What is the difference between prezygotic and postzygotic isolating mechanisms?

Answer 58

• Prezygotic mechanisms prevent two species from mating.
• Postzygotic mechanisms allow mating but prevent the development of viable, fertile offspring.

If these terms are unfamiliar, their names can give away their meaning. “Prezygotic” relates to events before zygote formation, while “postzygotic” relates to events that occur afterward.

Question 59

What is hybrid inviability?

Answer 59

Mating can occur and form a hybrid offspring, but that offspring will not develop into a healthy adult.

Hybrid inviability is an example of a postzygotic barrier between distinct species.

Question 60

What is hybrid breakdown?

Answer 60

Mating can occur and form healthy, fertile hybrid offspring. However, later hybrid generations (F2 and onward) are unhealthy and sometimes cannot reproduce themselves.

Hybrid breakdown is the final post-zygotic barrier that separates distinct species.

Question 61

What is hybrid sterility?

Answer 61

Mating can occur and form a healthy hybrid offspring. However, the hybrid is sterile and cannot reproduce.

Mules are examples of hybrid sterility, which is a postzygotic barrier between distinct species.

Question 62

One species of moth mates in the fall, while a nearby species of moth only mates in the spring. Which mechanism keeps these two species distinct?

Answer 62

Temporal isolation, a type of prezygotic isolation, separates these two species.

Temporal isolation usually relates to differences in mating seasons or times, though it can also separate nocturnal from diurnal species.

Question 63

One species of fish mate with another to produce viable offspring. When these offspring interbreed, their progeny are viable but sterile. Which mechanism keeps these two species distinct?

Answer 63

Hybrid breakdown, a type of postzygotic isolation, separates these two species.

Hybrid breakdown relates to a decrease in viability within progressive generations of hybrids.

Question 64

In a hypothetical situation, allele frequencies in a population remain unchanged over multiple generations. Though this condition does not occur naturally, it is often used as the basis for mathematical models. What term describes this situation?

Answer 64

Hardy-Weinberg equilibrium

Question 65

Name the five prerequisites for Hardy-Weinberg equilibrium.

Answer 65

1. Large population size
2. No mutation
3. No inward or outward migration
4. No natural selection
5. Random mating

Question 66

A very large, mutation-free population of finches is entirely isolated within their geographic area. Males tend to grow bright feathers to attract potential mates. What condition(s) of Hardy-Weinberg equilibrium does this population violate?

Answer 66

random mating

A large population size, lack of mutation, and lack of migration all fit Hardy-Weinberg criteria. However, if mates are chosen based on certain characteristics, mating is not random and equilibrium is violated.

Question 67

What two equations can be used when a population is assumed to be in Hardy-Weinberg equilibrium?

Answer 67

The main Hardy-Weinberg equation is p² + 2pq + q² = 1. Since this statement assumes that only two alleles are present, and these alleles are represented by “p” and “q,” p + q = 1 is also relevant.

For these equations to hold true, the proportion of each allele must be described in decimal form. For example, if the A allele comprises 36% of the gene pool, its frequency would be 0.36.

Question 68

In the Hardy-Weinberg equation, what variable or expression refers to the frequency of the dominant allele in the gene pool?

Answer 68

p

When dealing with Hardy-Weinberg, remember that alleles are denoted by single letters. Conventionally, the dominant allele is “p” and the recessive allele is “q.”

Question 69

In the Hardy-Weinberg equation, what variable or expression refers to the frequency of the heterozygous genotype in the gene pool?

Answer 69

2pq

Remember that genotypes in the Hardy-Weinberg equation are denoted by expressions, not single letters. p² represents the proportion of homozygous dominant individuals, while q² represents the frequency of the homozygous recessive genotype.

Question 70

A and a are the only two alleles that exist for a certain trait. In a stable population, 9% of individuals have the aa genotype. What percentage of individuals are heterozygous?

Answer 70

42%

The frequency of the homozygous recessive genotype, q², is 0.09. From this information, it can be found that q = 0.3. Since p + q = 1, p must be equal to 0.7. The heterozygote frequency, 2pq, is thus (2)(0.7)(0.3) or 0.42.

Question 71

How are genetic differences between two species used to quantify their evolutionary relationship?

Answer 71

Random mutations occur at a predictable rate. Thus, the differences between the genetic sequences of two species can be used to estimate the time since they diverged from a common ancestor.

Natural selection can increase the rate at which a certain mutation predominates, so this measurement is only an estimate.

Question 72

Which theory states that evolution occurs in short, rapid bursts within long periods of little change?

Answer 72

Punctuated Equilibrium Theory

According to this theory, a species will usually exist in a static state where virtually no evolutionary change occurs. This state is interrupted by brief periods of evolution that are prompted by specific events.

Question 73

The Miller-Urey experiment used water, methane, ammonia, and hydrogen gas to simulate the conditions of early Earth. What molecules were produced by this experiment?

Answer 73

Amino acids

This result, along with those of similar experiments, implied that organic biomolecules could be synthesized from inorganic substances. This was a major breakthrough in the study of the origin of life.

Question 74

What biochemical evidence supports the idea that all life descends from a common ancestor?

Answer 74

All living organisms encode their genetic material as DNA.

They also share the genetic code by which this material is converted into protein.

Specifically, DNA is transcribed into RNA, which is translated into protein.