BIO Exam #2: The Evolution of Populations

A giraffe and a mouse (both mammals) have the same number of vertebrae in their neck and spine. Which of the following accounts for this?

The vertebrae in their neck and spine are homologous because they share a common ancestor.

Sharks (which are fish) and dolphins (which are mammals) are both shaped like a torpedo. Which of the following accounts for this?

Their shape arose through convergent evolution, since that shape is beneficial for animals living in the ocean.

In evolutionary terms, an organism's relative fitness is measured by its __________.

Contribution to the gene pool of the next generation

Sexual dimorphism

Differences between the secondary sex characteristics of males and females of the same species.

Long necks make it easier for giraffes to reach leaves high on trees, while also making them better fighters in "neck wrestling" contests. In both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today?

Directional selection

Part complete Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to __________.

Directional selection

Three modes of selection: characteristics, phenotypic distributions

Directional selection: a mode of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction Disruptive selection: (or diversifying selection) a mode of natural selection in which extreme values for a trait are favored over intermediate values Stabilizing selection: a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value

Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers?

Disruptive selection

Which type of selection tends to increase genetic variation?

Disruptive selection

What is microevolution?

Evolution on its smallest scale, a change in allele frequencies in a population over generations

True or false? Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population.

False

Good Gene Hypothesis

Females choose mates whose genes improve their offspring's fitness. Males indicate their quality in some visible way (sing, dance, display ornaments).

What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?

Founder effect

Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?

Genetic drift

Distinguish genetic drift from gene flow in terms of (a) how they occur and (b) their implications for future genetic variation in a population.

Genetic drift results from chance events that cause allele frequencies to fluctuate at random from generation to generation; within a population, this process tends to decrease genetic variation over time. Gene flow is the exchange of alleles between populations, a process that can introduce new alleles to populations and hence may increase its genetic variation (slightly, since rates of gene flow are often low)

Founder effect: Characteristics (effects on microevolution) and examples

Genetic drift that occurs when few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population. EX: When a few members of a population are blown by a storm to a new island.

Explain why genetic variation within a population is a prerequisite for evolution.

Within a population, genetic differences among individuals provide the raw material on which natural selection and other mechanisms can act. Without such differences, allele frequencies could not change over time - and hence the population could not evolve.

What is the relative fitness of a sterile mule? Explain.

Zero, because fitness includes reproductive contributions to the next generation and a mule cannot produce offspring.

Bottleneck effect: Characteristics (effects on microevolution) and examples

Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population. EX: Can be caused by a natural disaster, like an earthquake or volcano eruption, and caused by humans through over-hunting, deforestation, and pollution.

Which statement correctly describes the role of chance in evolution?

Genetic variation does arise by chance mutations.

What are the types of mutations that get passed on to offspring in multicellular organisms?

Germline mutations

Where do new alleles come from, what is the ultimate (original) source of all biological variation?

Mutation

Is a mutation likely to be beneficial? Why or why not?

Mutation is not likely to be beneficial because it randomly changes generations of selection. It is not likely to improve adaptation.

Which of the following are causes of evolutionary change?

Mutation, Gene flow, Natural selection, Genetic drift

What is the smallest unit of evolution?

Population

How does the mutation rate and the effect of mutations differ in prokaryotes and animals?

Prokaryotes: mutations can quickly generate genetic variation; reproduce rapidly, short lifespans; haploid--single allele for each gene; a new allele can have immediate effects Animals: low mutation rates; slow generation time, long lifespans; diploid--two (or more) alleles for each gene; prevents most mutations from causing significant effects

Genetic drift: Characteristics (effects on microevolution) and examples

Random fluctuations of allele frequencies from generation to generation Effect: Helps to create more genetic variation in a population

A mutation that is neither harmful nor beneficial is termed a _______.

Silent mutation

Small Aristelliger lizards have difficulty defending territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these lizards?

Stabilizing selection

Women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies?

Stabilizing selection

What accounts for the majority of variation in sexually reproducing species?

The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises each generation during sexual reproduction.

Which of the following statements is FALSE?

Organisms can change their DNA in order to become better adapted to their environment.

Explain why natural selection is the only evolutionary mechanism that consistently leads to adaptive evolution in a population.

Because natural selection has a "sorting" effect, it consistently increases the frequency of alleles that improve the match between an organism and its environment.

How did Mendel's model of inheritance help explain Darwin's theory of natural selection?

By proposing a mechanism of how organisms could transmit discrete, heritable units to offspring

Of all the mutations that occur in a population, why do only a small fraction become widespread?

Only a small fraction of mutations are beneficial and increase the fitness of a species.

Independent assortment

Homologous chromosomes separate into gametes (egg or sperm) independently of other chromosomes pairs. Gametes vary extensively in their genetic makeup.

Crossing over

Homologous chromosomes trade some of their genes during meiosis producing unique combinations of maternal and paternal genomes

How is the process of evolution revealed by the imperfections of living organisms?

Imperfections in organisms result from a variety of other constraints, such as a lack of genetic variation for the trait. Organisms inherit a basic form from their ancestors, and that form is modified by natural selection over time. This form is usually not perfect.

Natural selection changes allele frequencies because some __________ survive and reproduce better than others.

Individuals

Why can't an individual evolve?

Individuals don't evolve, only populations. Individuals in a population vary, some in the population are better able to survive and reproduce given a particular set of environmental conditions.

Natural selection: Characteristics (effects on microevolution) and examples

Individuals with certain inherited traits survive and reproduce more than other individuals because of those traits Effect: Can change allele frequencies with fitness-increasing alleles becoming more common in the population

Characteristics and examples of intersexual and intrasexual selection

Intrasexual selection: sexual selection within the same sex. EX: a single male may patrol a group of females and prevent other males from mating with them. The patrolling male may defend his status by defeating smaller, weaker, or less fierce males in combat. Intersexual selection: aka mate choice, individuals of one sex (usually the females) are choosy in selecting their mates from the other sex. EX: bright plumage may make male birds more visible to predators. But if such characteristics help a male gain a mate, and if this benefit outweighs the risk from predation, then both the bright plumage and the female preference for it will be reinforced because they enhance overall reproductive success

What is the role of variation in evolution?

It allows natural selection to increase or decrease frequency of alleles already in the population. It is advantageous to a population because it enables some individuals to adapt to the environment while maintaining the survival of the population.

Generation-to-generation change in the allele frequencies in a population is _____.

Microevolution

Which of the following is true of microevolution?

Microevolution is a generation-to-generation change in allele frequency.

Which of the following consistently improves the degree to which organisms are well suited for life in their environment?

Natural selection

Which of the three mechanisms (natural selection, gene flow, and genetic drift) consistently leads to adaptive evolution? Why?

Natural selection because it only acts on the population's heritable traits: selecting for beneficial alleles and, thus, increasing their frequency in the population, while selecting against deleterious alleles and, thereby, decreasing their frequency.

In what sense is natural selection more "predictable" than genetic drift?

Natural selection is more predictable in that it alters allele frequencies in a nonrandom way: it tends to increase the frequency of alleles that increase the organisms; reproductive success in its environment and decreases the frequency of alleles that decreases the organism's reproductive success. Alleles subject to genetic drift increase or decrease in frequency by chance alone, whether or not they are advantageous.

What three mechanisms that cause microevolution?

Natural selection, gene flow, and genetic drift can alter allele frequencies in a population

Does natural selection result in perfect organisms? Why or why not?

No, it cannot. Natural selection cannot create novel, perfect species because it only selects on existing variations in a population.

The evolutionary effects of genetic drift are greatest when __________.

The population size is small

Random mating

The random union of egg and sperm produces a zygote that has a unique assortment of alleles

Gene flow: Characteristics (effects on microevolution) and examples

Transfer of allele into or out of a population due to the movement of fertile individual of their gametes Effects: Gene flow affects microevolutionary change because you can gain or lose alleles due to immigrants and emigrants