Evolution and Natural Selection Flashcards
Define:
Evolution
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.
Define:
Natural selection
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.
What qualities are exhibited by an organism with high fitness?
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.
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?
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.
What genetic value changes within a population as evolution occurs?
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.
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
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.
Define:
Group selection
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.
What measurement determines the evolutionary success of an allele?
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.
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
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.
What condition must be met for a group of individuals to be considered part of the same species?
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.
Horses and donkeys can mate and produce healthy offspring called mules. Why are horses and donkeys considered separate species?
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.
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?
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.
Viceroy butterflies mimic the appearance of monarch butterflies to repel predators. Is the evolution of this trait an example of adaptation or specialization?
adaptation
Through natural selection, this mimicry has evolved to increase survival. However, sharing the appearance of monarch butterflies does not fill a unique niche.
Define:
Ecological niche
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.
What will occur between two different species of ant that occupy the same niche?
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.
How does intraspecies competition affect population growth?
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.
At one point, overhunting caused the American bison population to drop to fewer than 1000 individuals. What term describes this situation?
bottleneck
Bottlenecks can dramatically change the gene pool, since all subsequent members of the species descend from a small number of individuals.
What kind of factors promote genetic drift?
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.
What occurs when two groups undergo divergent evolution?
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.
What occurs when two groups undergo parallel evolution?
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.
What occurs when two groups undergo convergent evolution?
It causes unrelated, originally dissimilar groups to become increasingly similar.
This often occurs when two species begin to fill the same ecological niche.
What type of evolution is demonstrated by bats and owls?
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.
Which type of evolution can result in the existence of analogous structures?
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.
What is the difference between ontogeny and phylogeny?
- 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.
Is the development of a fertilized egg into an adult chicken an example of ontogeny or phylogeny?
ontogeny
Ontogeny refers to an organism’s development over its lifetime, while phylogeny refers to a species’s development over evolutionary time.
How are genetic differences between two species used to quantify their evolutionary relationship?
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.
What biochemical evidence supports the idea that all life descends from a common ancestor?
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.
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.
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.
Which type of selection best relates to antibiotic-resistant bacteria?
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.
Define:
Inbreeding
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.
Define:
Outbreeding
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.
What term describes a major reduction in the number of individuals in a population?
bottleneck
Bottlenecks are generally caused by catastrophic events, whether environmental (such as a natural disaster) or human-related.
Define:
Homologous structures
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.
Define:
Analogous structures
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.
Which type of natural selection is shown in the image below?
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.
Which type of natural selection is shown in the image below?
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.
Which type of natural selection is shown in the image below?
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.
Our modern understanding of evolution stems largely from the findings of which individual, who proposed the concept of natural selection?
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.
