ch 19 part 2 Flashcards
individuals with heritable, favorable traits have increased survival and reproduction, and the traits become more common in the population.
Natural Selection
What is reproductive success?
The likelihood of contributing fertile offspring to the next generation
Natural selection acts on traits that favor reproductive success, which includes traits that increase ______ and traits directly associated with ______.
survival; reproduction
Natural selection results in a population better adapted to its environment because
only individuals who are well adapted to the environment contribute their alleles to the next generation.
Consider a gene with two alleles, B and b. In a certain population, on average, genotype BB produces 2 offspring, genotype Bb produces 3 offspring, and genotype bb produces 5 offspring. What is the value for wBB?
.40
Suppose an animal with genotype AA produces an average of 8 offspring, genotype Aa produces an average of 12 offspring, and genotype aa produces an average of 3 offspring, which genotype is the most fit?
Aa
The likelihood that an individual will contribute fertile offspring to the next generation is called
Reproductive success
Select the types of selection that tend to increase or maintain genetic diversity within a population.
Balancing selection
Disruptive selection
Select the main categories of traits that contribute to reproductive success and that are favored by natural selection.
Traits associated directly with reproduction
Traits that increase survival to reproductive age
In seedcracker finches from Cameroon, small- and large-billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population?
Directional selection
Natural selection changes allele frequencies in populations because some
individuals with favorable traits survive and reproduce more successfully than others.
Suppose in a certain population an animal with the genotype BB produces 4 offspring, genotype Bb produces 6 offspring, and genotype bb produces 2 offspring. What is the relative fitness of genotype bb?
Multiple choice question.
0.33
Which of the following is an example of stabilizing selection?
Newborn babies of intermediate weight are most likely to survive; both high and low birthweights are associated with increased infant mortality.
If genotype AA produces an average of 5 offspring, genotype Aa produces an average of 3 offspring, and genotype aa produces an average of 2 offspring, which genotype is the most fit?
AA
directional selection
Choice, favors one extreme phenotype favors one extreme phenotype
stabilizing selection
favors the intermediate phenotype
diversifying selection
favors both extreme phenotypes but selects against intermediate phenotypes
balancing selection
favors heterozygosity, or can favor the uncommon allele
Which of the following is an example of directional selection?
An increase in the number of mice with brown fur compared to the number of mice with white fur.
Which of the following is an example of diversifying selection?
Strains of colonial bentgrass in Wales are either metal-sensitive or metal-resistant; intermediate tolerance of metal is rarely observed.
A starting population of light fur mice has a mutation that produces a brown colored mouse. This gives it a selective reproductive advantage because it less susceptible to predation and can reproduce more frequently than the light colored mice. Over many generations there is a selection for the darker colored mouse. This is an example of which of the following?
directional selection,
Birds that lay intermediate numbers of eggs have greater fitness than birds that lay either too many or too few eggs. This is an example of
stabilizing selection.
The maintenance of the sickle-cell anemia alleles in populations living in areas where malaria is prevalent is an example of ______ selection.
balancing
In which of the following patterns of natural selection are the extremes of a phenotypic distribution selected against?
Stabilizing selection
Natural selection may fail to eliminate a less-fit allele from a population due to
heterozygote advantage.
In negative frequency-dependent selection, the fitness of a genotype ______ when its frequency becomes higher.
decreases
The black bellied seed cracker, Pyrenestes, is a West African finch. Within the same geographic region, two subspecies of the finch are found. One subspecies has a large beak, which is efficient at cracking the hard seeds of the sedge, Scleria verrucosa. The other subspecies has a small beak, which is more efficient at eating the soft seeds of the sedge, Scleria goossensii. What type of selection occurred to produce this situation?
Diversifying selection
What type of traits does sexual selection tend to favor?
Traits that increase an individual’s ability to find a mate and mate successfully
Which of the following is an example of balancing selection?
The sickle-cell anemia allele is prevalent in populations living in areas where malaria is present.
Sexual selection can lead to a significant difference in appearance between the two sexes, which is called
sexual dimorphism.
In some situations, the heterozygous genotype for a single gene has higher fitness than either of the corresponding homozygous genotypes. This phenomenon is calle
heterozygote advantage.
If individuals with rare phenotypic variants tend to have the highest fitness for a particular trait, the trait is likely subject to
negative frequency-dependent selection.
The term “genetic drift” refers to the fact that allele frequencies tend to “drift” ______ from generation to generation due to chance.
randomly
How did Peter and Rosemary Grant show that the beak size of finches on the island of Daphne Major is affected by natural selection?
When only large seeds were available for food, finches with larger beaks were more likely to survive and pass this trait on to offspring.
What type of selection affects traits that directly influence an individual’s ability to mate successfully?
Sexual selection
How does genetic drift affect allele frequencies in a population?
It changes allele frequencies without regard for their fitness.
A significant difference in the appearance of the two sexes within a species is called a(n) and is often the result of sexual selection.
sexual dimorphism
Genetic drift can lead to the ____ or ______ of alleles in a population.
increase or decrease
What is the difference between intrasexual selection and intersexual selection?
Intrasexual selection occurs between members of one sex, while intersexual selection occurs between members of opposite sexes
In genetic drift, allele frequencies change due to
random chance.
The founder effect and the bottleneck effect are both examples of how ______ can rapidly alter allele frequencies when the size of a population dramatically decreases.
genetic drift
After a population bottleneck, the allele frequencies of the surviving population are likely to change due to
genetic drift.
True or false: Genetic drift causes alleles that increase fitness to become more common in a population.
false
Genetic characteristics of a population that has experienced the founder effect include which of the following?
Less genetic variation than the original larger population
Different allele frequencies than the original larger population
What are possible outcomes of genetic drift?
Fixation of an allele
Loss of an allele
Genetic drift selects for
no particular allele.
Which of the following can lead to genetic drift within a population?
The bottleneck effect
The founder effect
Neutral variation describes changes in genes and proteins that do not affect
reproductive success.
What happens after a population passes through a bottleneck?
The surviving members of the population may have different allele frequencies than the original population
What consequences does the founder effect have on the founding population? Choose all that apply.
The founding population will likely have less genetic variation than the larger original population.
Allele frequencies may be markedly different in the founding population than they were in the original larger population.
Motoo Kimura’s theory of neutral variation proposed that alleles that do not affect reproductive success may become common in a population due to
genetic drift.
True or false: Due to genetic drift, alleles with high fitness tend to become fixed in populations, and alleles with lower fitness tend to become lost.
False
Genetic drift explains ______ variation in a population, and natural selection explains ______ variation in a population due to evolution.
neutral; adaptive
Genetic drift can promote variation, which are changes in genes and proteins that do not affect reproductive success.
neutral
Migration increases genetic diversity within populations because it
introduces new alleles into the population.
How does migration affect allele frequencies between two neighboring populations?
It makes them more similar.
Individuals who choose mates depending on phenotypic similarity or genetic relatedness are experiencing
nonrandom mating.
Which statements are components of Motoo Kimura’s theory of neutral variation?
- Much of the genetic variation in natural populations is neutral.
- Neutral alleles can become common in a population due to genetic drift.
Assortative mating, nonassortative mating, and inbreeding are all forms of
nonrandom mating.
_____ explains the accumulation of neutral variation in a population, and ______ explains adaptive changes in a species due to evolution.
Genetic drift; natural selection
Because migration leads to gene flow, it tends to ______ genetic diversity within populations.
increase
Migration tends to reduce ______ between two neighboring populations.
allele frequency differences
When mating is ____, individuals choose their mates based on similar phenotype, dissimilar phenotype, or genetic lineage.
nonrandom
Which of the following are forms of nonrandom mating?
Inbreeding
Preferential mating of individuals with dissimilar phenotypes
Selection of mates with similar phenotypes
