Ch.24 - Evolution of PopulationsSee all chapters
All Chapters
Ch.1 - Introduction to Biology
Ch.2 - Chemistry
Ch.3 - Water
Ch.4 - Carbon
Ch.5 - Biological Molecules
Ch.6 - Cells
Ch.7 - The Membrane
Ch.8 - Energy and Metabolism
Ch.9 - Respiration
Ch.10 - Photosynthesis
Ch.11 - Cell Signaling
Ch.12 - Cell Division
Ch.13 - Meiosis
Ch.14 - Mendelian Genetics
Ch.15 - Chromosomal Theory of Inheritance
Ch.16 - DNA Synthesis
Ch.17 - Gene Expression
Ch.18 - Regulation of Expression
Ch.19 - Viruses
Ch.20 - Biotechnology
Ch.21 - Genomics
Ch.22 - Development
Ch.23 - Evolution by Natural Selection
Ch.24 - Evolution of Populations
Ch.25 - Speciation
Ch.26 - History of Life on Earth
Ch.27 - Phylogeny
Ch.28 - Prokaryotes
Ch.29 - Protists
Ch.30 - Plants
Ch.31 - Fungi
Ch.32 - Overview of Animals
Ch.33 - Invertebrates
Ch.34 - Vertebrates
Ch.35 - Plant Anatomy
Ch.36 - Vascular Plant Transport
Ch.37 - Soil
Ch.38 - Plant Reproduction
Ch.39 - Plant Sensation and Response
Ch.40 - Animal Form and Function
Ch.41 - Digestive System
Ch.42 - Circulatory System
Ch.43 - Immune System
Ch.44 - Osmoregulation and Excretion
Ch.45 - Endocrine System
Ch.46 - Animal Reproduction
Ch.47 - Nervous System
Ch.48 - Sensory Systems
Ch.49 - Muscle Systems
Ch.50 - Ecology
Ch.51 - Animal Behavior
Ch.52 - Population Ecology
Ch.53 - Community Ecology
Ch.54 - Ecosystems
Ch.55 - Conservation Biology

Genetic Variation

See all sections
Hardy-Weinberg Model
Genetic Variation

Concept #1: Inbreeding and Sexual Selection

Concept #2: Directional, Stabilizing, and Disruptive Seleciton

Concept #3: Balancing Selection and Gene Flow

Additional Problems
A population ecologist observes that the surface area of leaves in a species of dandelion growing in a desert is much smaller compared to the larger surface area of leaves of the same species growing in areas that receive greater rainfall. She gathers seeds from individual plants growing at both low and high rainfall locations, plants them in a uniform environment in a greenhouse, and measures the leaf area of the new plants. All of her experimentally grown plants grow to have similar leaf surface areas. From this she concludes that _____.a. leaf surface area is not an adaptive trait that promotes fitnessb. the variation she originally observed was due to genetic differencesc. the variation she originally observed was due to disruptive selectiond. the variation she originally observed was an example of non-genetic environmental influencee. stabilizing selection was responsible for leaf-area differences in the parent plants
One spring, a dust storm blankets the usually green garden where a species of fraggles forage for food in gray dust. Under these conditions, the green fraggles become very visible to the Gorgs, monstrous beasts who tend the gardens and try to kill fraggles to protect their crops. The gray fraggles, however, now blend into the dusty background and find that they can easily steal radishes without detection. How might this affect microevolution in this population of fraggles?a. the gray fraggles will likely become a new species over timeb. the proportion of the gray fraggles will increase in the population over timec. green fraggles learn to forage at night to escape detectiond. green fraggles have more offspring per litter to compensate for their higher mortalitye. green fraggles reproduce more often to compensate for their higher mortality
In crossbill birds the beaks have a specialized shape to allow the crossbills to extract pine seeds out of cones. Crossbills in one forest feed on two different pine species. For one kind of cone a long thin beak is most efficient while in the other type of cone a short thick beak is most efficient. What evolutionary force is likely happening on beak shape?a. disruptive selection                    b. genetic driftc. gene flowd. intrasexual selectione. frequency dependent selection
Which of the following is a correct definition of gene flow (migration)?a. random change in allele frequency over timeb. movement of alleles between populationsc. changes in allele frequency over timed. changes in genotype frequencye. accidental changes in DNA structure
Which type of evolutionary force can maintain genetic variation?a. directional selection  b. stabilizing selection   c. genetic driftd. mutation      
In the sage grouse males congregate at areas called leks. Females visit leks and move around, observing the displays of different males. Eventually each female will stop and mate with one of the males, perhaps at a second visit. This is an example of?a. directional selectionb. stabilizing selectionc. disruptive selectiond. intersexual selectione. intrasexual selection
Without genetic diversity, a population might more easily fall victim to parasites and pathogens. a. Trueb. False
Crickets living high on a mountain have a high frequency of alleles for cold tolerance. Storms frequently blow crickets off the mountain down to lower elevations where they mate with crickets lacking the cold tolerant alleles, thus increasing the allele frequency in the low elevation population. This is an example ofa. genetic driftb. gene flowc. mutationd. sexual selection
Through time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing _______.a. nonrandom reproductionb. genetic driftc. geographic isolationd. gene flowe. mutations.
The entire collection of genes and their alleles is a population's: a.  Genotypeb.  Phenotypec.  Dominant traitsd.  Recessive traitse.  Gene pool
Cattle breeders have improved the quality of meat over the years by which process?a. directional selectionb. artificial selectionc. stabilizing selectiond. A and Be. A and C
The mode of natural selection in which one extreme phenotype is fittest and the environment selects against the others is: a.  Directional selectionb.  Disruptive selectionc.  Stabilizing selectiond.  Artificial selectione.  Convergent selection
Which of the following is most likely to have been produced by sexual selection?a. camouflage coloration in animalsb. a male lion's manec. different sizes of male and female pineconesd. the ability of desert animals to concentrate their urine
The mode of natural selection in which two or more extreme phenotypes are fitter than the intermediate phenotype is: a.  Directive selectionb.  Stabilizing selectionc.  Disruptive selectiond.  Artificial selectione.  Convergent selection
When imbalances occur in the sex ratio of sexual species that have two sexes (i.e., other than a 50:50 ratio), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. This is most clearly an example of _______ selection.a. frequency-dependentb. sexualc. disruptived. balancinge. stabilizing
The mode of natural selection in which extreme phenotypes are less fit than the optimal intermediate phenotype is: a.  Directive selectionb.  Disruptive selectionc.  Stabilizing selectiond.  Artificial selectione.  Convergent selection
The three types of natural selection are: a.  Directional selection, convergent selection, and disruptive selectionb.  Directional selection, artificial selection, and convergent selectionc.  Disruptive selection, stabilizing selection, and normalizing selectiond.  Disruptive selection, stabilizing selection, and artificial selectione.  Directional selection, disruptive selection, and stabilizing selection
"Balanced polymorphism" means that: a.  Many genes that affect the same trait persist indefinitely in a populationb.  Multiple alleles of a gene persist indefinitely in a populationc.  Only a dominant and recessive allele exist for each trait in a populationd.  Many traits persist in a population that are controlled by only a single allelee.  None of the above are correct
The fact that individuals whose red blood cells break down more rapidly in an area where malaria is more prevalent have a better chance of reaching reproductive age is known as: a.  Heterozygote advantageb.  Homozygote advantagec.  Polygenic inheritanced.  Heterozygote disadvantagee.  Pleiotropy
Sexually dimorphic features do not include:  a.  Colored plumage b.  Intelligence c.  Antlers d.  Body size e.  None are sexually dimorphic features
One concern of conservation biologists is that endangered species will have low genetic diversity due to a small population size. Why is this a concern? a.  Because individuals in small populations acquire mutations more slowly than those in large populationsb.  Because sexual selection is stronger in small populationsc.  Because if a disease occurs in the population there may not be organisms with resistant alleles 
Babies that are at a low birth weight are more likely to have health problems, while women will have difficulty delivering babies with high birth weight. Together this leads to ______ for babies of average birth weight. a.  Stabilizing selectionb.  Disruptive selectionc.  Directional selectiond.  Artificial selection 
Ancestors of giraffes with shorter necks could not reach branches high up in trees for food. This led to ____ for longer necked giraffes. a.  Stabilizing selectionb.  Disruptive selectionc.  Artificial selectiond.  Sexual selectione.  Directional selection
Ancestors of the Galapagos finches had two different types of seeds to eat on some islands. Some seeds were very small, and required small beaks to handle, other seeds were very large and required large strong beaks to crack. This led to ____ among the Galapagos finches. a.  Directional selectionb.  Stabilizing selectionc.  Disruptive selectiond.  Artificial selectione.  Sexual selection
Carriers of cystic fibrosis have some protection against intestinal infections such as cholera. However, people with two copies of the cystic fibrosis allele develop a life-threatening disease. The mutant allele is very common in people of northern European descent because of: a.  Disruptive selectionb.  Directional selectionc.  Artificial selectiond.  Sexual selectione.  Stabilizing selection
Alleles conferring red plumage to cardinal males are common because red plumage: a.  Makes males less susceptible to predationb.  Is helpful in attracting preyc.  Is preferred by female cardinals in choosing a mated.  Allows male cardinals to easily identify each othere.  Is an example of genetic drift
A male peacock has enormous tail feathers that it uses in mating displays to attract females. While the tail feathers are an advantage in mating, what is the potential disadvantage of these feathers to the male? a.  The feathers require a lot of energy to produceb.  Bright feathers make males less susceptible to predationc.  The feathers make the male more attractive to other malesd.  There are no disadvantages to having large tail featherse.  The large tail feathers would make it easier to fly
The founder effect: a.  Occurs when large groups of individuals leave their home population and establish new settlements, mating only among themselvesb.  Occurs when small groups of individuals leave their home population and establish new settlements, mating only among themselvesc.  Occurs when many members of a population die, resulting in a great loss of genetic diversityd.  Occurs when many members of a population reproduce causing too much genetic diversity within the population
The bottleneck effect: a.  Occurs when many members of a population die, resulting in a great loss of genetic diversityb.  Occurs when many members of a population reproduce causing too much genetic diversity within the populationc.  Occurs when small groups of individuals leave their home population and establish new settlements, mating only among themselvesd.  Occurs when large groups of individuals leave their home population and establish new settlements, mating only among themselves
The few ancestors of the Galapagos finches who colonized the islands would be an example of: a.  A bottleneckb.  Natural selectionc.  Increased mutation rated.  Gene flowe.  Founder effect
The North American bison was hunted to near extinction in the 1800s, and has since recovered, but with decreased genetic diversity. This is an example of: a.  Founder effectb.  A bottleneckc.  Natural selectiond.  Increased mutation ratee.  Gene flow
Refer to the figure below. Which description of the gene pool shown is correct?a. Size of gene pool = 30b. Frequency of X1= 0.80c. Population size = 60d. Frequency of X1X3 = 0.10e. Number of genes = 2
Describe the two ways the genetic variation is increased through meiosis and indicate during which stage of meiosis the process occur. 
A mutation that changes a glutamate is found to lead to a loss of activity in a protein. However, activity is regained when a second mutation at a different position changes an alanine residue to aspartate. How might this double mutant (E to Q with A to E) lead to a restoration of activity?Hint: These secondary mutations are sometimes called compensatory mutations.2nd Hint: Think three dimensionally.
Which definition of evolution is correct and complete?A. Evolution is the survival of the fittest over generations.B. Evolution is the change in fitness of a species.C. Evolution is the change in allele frequencies of a population over generations.D. Evolution is natural selection within species.
Can genetic drift lead to adaptations? Why or why not?
Identify the three major events/processes that result in genetic variation between parents and offspring.
Why does meiosis result in more genetic variation than can be explained by mutation alone? Select all that apply.A. because of the events of meiosis IB. because of the events of meiosis IIC. because of crossing overD. not all the DNA gets replicated
The only source of new alleles in species is _________.A. mitosisB. mutationC. speciationD. genetic driftE. sexual reproduction
Which of the following is false?A. If a genetic disease reduces fertility and the allele that causes the disease offers no other advantage, the allele will likely eventually disappear, due to natural selection.B. Natural selection does not favor individuals who are homozygous for the sickle-cell allele, because these individuals typically die before they are old enough to reproduce.C. Individuals who are heterozygous HbA/HbS are protected from malaria, and this is why sickle-cell disease persists in wetter, mosquito-ridden regions in Africa.D. In regions where malaria does not occur, individuals who are heterozygous HbA/HbS have a fitness advantage over those who are homozygous for the normal hemoglobin allele (HbA).
Single nucleotide polymorphismsA. are often found in humansB. are rarely found in humansC. arise from gene duplicationsD. arise from transposonsE. are only found in open reading frames