Biology Chapter 23
In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following?
The value of a particular characteristic; characteristics of an organism can include such traits as size and color.
The gene pool of a population consists of __________.
all copies of every type of allele at every locus in all members of the population
When should a lactase supplement be taken in order to be most effective, and why?
at the same time the dairy product is consumed, so that the lactase will be in contact with the lactose
Phenotypic variation
can be the result of mutations in the coding regions of DNA.
In evolutionary terms, an organism's relative fitness is measured by its ________
contribution to the gene pool of the next generation **Those organisms with adaptations best suited to the current environment will make the most significant contribution to the next generation.
Relative fitness
defined by the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals.
Gene variability
describes genetic variation at the whole-gene level, which would not be the result of mutations in noncoding regions of DNA.
neutral variation
differences in DNA sequence that do not confer a selective advantage or disadvantage.
Stabilizing selection __________.
favors intermediate variants in a population
The enzyme lactase breaks the sugar lactose into which compound(s)?
galactose glucose
One of the following is NOT a source of genetic variation?
genetic drift
One population of a species has 25 individuals, all with genotype AAAA; a second population of this species has 40 individuals, all with genotype aaaa. Assume that these populations live far apart but in similar environmental conditions. Based on this information, the observed genetic variation most likely resulted from
genetic drift
Which of the following are causes of evolutionary change?
genetic drift gene flow mutation natural selection
Neutral variation
genetic variations that have little or no impact on reproductive success
In which country would you most likely find a higher incidence of lactase persistence?
in a Scandinavian country where people historically raised dairy cattle and made cheese
Which of the following is true of microevolution?
it is the kind of evolution that can change the relative abundance of a particular allele in a gene pool over the course of generations
Sexual recombination includes the shuffling of chromosomes in __________ and fertilization.
meiosis
5 Assusmptions of the Hardy-Weinberg model.
no selection at the gene in question; no genetic drift; no gene flow; no mutation; random mating.
The sickle-cell allele, which is recessive, causes anemia but confers resistance to malaria in individuals who possess it. However, homozygous recessive individuals often die from anemia but not from malaria, and homozygous dominant individuals do not have anemia but could die from malaria. Heterozygous individuals have the highest relative fitness. This is an example of __________.
the heterozygote advantage
No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is __________.
the reshuffling of alleles in sexual reproduction
No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is
the reshuffling of alleles in sexual reproduction.
Population variation
the result of genetic variation in coding regions of DNA.
Protein variability
the result of mutations in coding regions of DNA.
You read about soapberry bugs and select the correct statement describing relative fitness in these individuals.
A soapberry bug with high relative fitness has a relatively high number of offspring that survive to reproductive age.
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 Disruptive selection causes both extreme phenotypes (large and small beaks) to be favored over the intermediate phenotypes.
Which type of selection tends to increase genetic variation?
Disruptive selection eliminates phenotypes near the average and favors the extreme phenotypes, resulting in increased genetic variation in a population.
Which of the following are basic components of the Hardy-Weinberg model?
Frequencies of two alleles in a gene pool before and after many random matings ***Hardy and Weinberg were trying to determine how and whether allele frequencies in a population change from one generation to the next.
Generation-to-generation change in the allele frequencies in a population is _____.
Generation-to-generation change in the allele frequencies in a population is the definition of microevolution.
Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?
Genetic Drift
Your friend wants a cat but doesn't want to brush it. Which of the following is true?
Get a long-haird ragdoll
Which of the following would seem to be an example of neutral variation?
Human fingerprints
Consider a population of wildflowers in which the frequency of the red allele CR is p = 0.7.
If the frequency of the red allele is p, and the frequency of the white allele is q, we know that p + q = 1. Since p = 0.7, we know that q = 0.3.
How is the process of evolution revealed by the imperfections of living organisms?
Organisms inherit a basic form from their ancestors, and that form is modified by natural selection over time. This form is usually not perfect. Imperfections in organisms result from a variety of other constraints, such as a lack of genetic variation for the trait.
According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if __________ is the only process acting on the gene pool.
Random sexual reproduction does not change the frequency of alleles in the gene pool.
Which of the following statements is not a part of the Hardy-Weinberg principle?
The genotype frequencies in the offspring generation must add up to two.
You have a housecat. Which of the following would likely work the best for your cat?
a brush that penetrates her fur and reaches the skin
Consider the following mutations to the nucleotide sequence of a gene. Which of these would be a frameshift mutation?
a single nucleotide-pair insertion
In a large population of randomly breeding organisms, the frequency of a recessive allele is initially 0.3. There is no migration and no selection. Humans enter this ecosystem and selectively hunt individuals showing the dominant trait. When the gene frequency is reexamined at the end of the year, __________.
the frequency of the homozygous dominants will go down, the frequency of the heterozygous genotype will go down, and the frequency of the homozygous recessives will go up
Balancing selection
occurs when natural selection maintains two or more forms in a population. - Heterozygote advantage
Stabilizing selection
reduces variation and maintains the status quo for a particular phenotypic character
Directional selection
selection for a single form; selection for two or more forms is balancing selection.
Which of the following statements correctly describes a population in Hardy-Weinberg equilibrium?
Allele and genotype frequencies in the population will remain constant from generation to generation.
This Punnett square shows allele combinations for all possible genetic crosses in the wildflower population described in Part A. (Punnet square available in Notes Chap 23)
Under Hardy-Weinberg equilibrium, the frequency of genotype CRCR (red flowers) in the offspring generation is expected to be p 2, or 0.49. The frequency of genotype CRCW (pink flowers) in the offspring generation is expected to be 2pq, or 0.42. The frequency of genotype CWCW (white flowers) in the offspring generation is expected to be q 2, or 0.09.
The evolutionary effects of genetic drift are greatest when __________.
Changes in the gene pool of a small population are frequently due to genetic drift.
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
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 drives the average of the population in one direction, in this case, toward longer necks.
A population of squirrels is preyed on by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome?
Disruptive selection
Which type of mutation plays the most important role in increasing the number of genes in the gene pool?
Duplication
In the context of populations, how do we define evolution?
Evolution is a change in a population's allele frequencies 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 Heterozygote advantage results in more genetic variation in the population.
Which of the following statements explains why male peacocks with brightly colored feathers are more prevalent than those with plain colors?
Female peacocks choose the showiest males as mates, causing this trait to be more prevalent in the population.
At what level does gene variability quantify genetic variation?
Whole-gene - Genetic variation at the whole-gene level (gene variability) can be quantified as the average percentage of loci that are heterozygous. May not vary in characteristic, but the genes may differ.
Which of the following is the best example of gene flow?
Wind blows pollen from one population of plants to another and cross-fertilization occurs.
Natural selection leads to adaptation, but there are many organisms on Earth that exhibit characteristics that are less than ideal for their environment. Which of the following statements correctly explain(s) this?
Adaptations are often compromises. Selection can act only on existing variations. Chance, natural selection, and the environment interact. Evolution is limited by historical constraints.
Why should we not view lactose intolerance as a disease in adult humans?
Adult humans did not consume dairy products until fairly recently in our evolutionary history.
How could milk-drinking have provided strong favorable selection for lactase persistence?
Milk is protein and fat-rich and therefore could have been an important, high-quality food source. Milk may have been a critical food source during times of famine. Milk was safer to drink than water and reduced exposure to pathogens.
The original source of all genetic variation is __________.
Mutation
Which of the following can form entirely new alleles?
Mutation
Which of the following evolutionary forces could create new genetic information in a population?
Mutations, which are changes in a cell's DNA, can introduce new genetic information in a population.
Which of the following evolutionary forces consistently results in adaptive changes in allele frequencies?
Selection is the only evolutionary force that consistently results in adaptation. Mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations.
Which statement below is true about sexual selection?
Sexual selection can result in sexual dimorphism—marked differences between the sexes in secondary sexual characteristics that are not associated directly with reproduction.
Suppose that a mutation for lactase-persistence occurred in each of the populations described below. In which populations would the mutation be more likely to increase in frequency over time because of natural selection?
Sheep can provide milk, which has about the same amount of lactose as cow's milk. Therefore, a lactase-persistence mutation could potentially be advantageous in this population.
Today there are alternatives to breast milk, such as lactose-free formula and soy milk, so lactose intolerant infants can survive.
Sickle cell disease and malaria are both potentially lethal diseases.
Predict what will happen to the frequency of the sickle cell allele in areas where malaria has been eradicated.
Sickle cell frequency will decrease
The authors designed a field experiment to test the hypothesis that competitive interactions between the closely related A. segrei (an introduced species) and A. carolinensis (a native species) would cause a change in the perch height of A. carolinensis.
Six islands were studied. A. sagrei was introduced on three of the islands, and the other three islands were used for comparison. Islands of three different sizes were selected (2 large, 2 medium, and 2 small) and the same experiment was run on each pair of islands.
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 causes no change in the average of the population; extreme phenotypes (in this case, large and small babies) become less common.
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 causes no change in the average of the population; extreme phenotypes (large and small lizards) become less common.
You invent a new cat brush that mimics a cat's tongue. Which of the following liquids does your brush contain?
Synthetic cat saliva
What is the frequency of the A1A2 genotype in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?
The calculation to determine the frequency of the A1A2 genotype is: 80 A1A2 individuals / (20 + 80 + 100) total individuals = 0.4, the frequency of the A1A2 genotype.
A fruit fly population has a gene with two alleles, A1A1 and A2A2. Tests show that 70%% of the gametes produced in the population contain the A1A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1A1 and A2A2?
.42
How may mutation, natural selection, genetic drift, and gene flow have affected populations that colonized the lake?
1. Natural Selection 2. Genetic Drift 3. Allele frequencies 4. Mutations 5. Gene flow 6. New alleles
In order to have reached this conclusion, the Grants must have either assumed or proven that several other facts about the finch population were true. Which statements represent information that must be true in order for the Grants conclusion to be correct?
Beak size varies among the birds in the finch population under study. Birds that could eat larger, tougher seeds survived and reproduced during the drought. Beak size is an inherited trait in the finch population under study.
A hurricane hits a small island, killing all but a few members of a bird population. This is an example of __________.
BottleNeck Effect
In the beetles described in the animation, there were two alleles for color, brown and green. Suppose that you discover a very small population of these beetles, consisting of the individuals shown below. How can you calculate the frequency of each allele in this population?
Brown Alleles 8 20 .4 .6
Which of the following statements correctly describe(s) characteristics of genetic drift
It can cause harmful alleles to become fixed in a population. It is significant in small populations. It can cause allele frequencies to change at random. It can lead to a loss of genetic variation in a population.
Natural selection changes allele frequencies because some _______ survive and reproduce better than others.
Individuals
How does diploidy help to preserve genetic variation?
It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes. Natural selection tends to decrease genetic variation. Recessive alleles are shielded from natural selection in heterozygotes.
Adult humans did not consume dairy products until fairly recently in our evolutionary history.
Lactase breaks down lactose into smaller molecules that can be absorbed by the cells that line the small intestine.
Most people are lactose intolerant as adults, but nearly everyone produces sufficient lactase as an infant. However, in some cases, genetic mutations can occur that make an infant lactose intolerant. From an evolutionary perspective -- over thousands of years -- why would lactose intolerance in infants be very rare in the population?
Lactose intolerant infants could not digest breast milk and therefore usually died, never having the chance to pass the mutation on to their children.
The three major mechanisms of evolution differ in how they work, and as a result often have different effects on a population. Review your understanding of natural selection, genetic drift, and gene flow by sorting the statements below into the correct bins.
Natural Selection: -consistently causes a population to become better adapted to its environment -a result of differential success in reproduction -cannot cause a harmful allele to become more common Genetic Drift:-responsible for the founder effect -causes allele frequencies to fluctuate randomly -responsible for the bottleneck effect Gene Flow: -a result of the movement of fertile individuals or their gametes -can introduce new alleles into a population's gene pool
All of the following conditions are required for Hardy-Weinberg equilibrium except __________.
Natural selection
What is the only evolutionary mechanism that consistently leads to adaptive evolution?
Natural selection Because natural selection has a sorting effect, it consistently increases the frequency of alleles that improve the match between an organism and its environment.
Natural selection, genetic drift, and gene flow cause a population to evolve in different ways.
Natural selection is the result of differential survival and reproduction. It is the only mechanism of evolution that consistently causes a population to become better adapted to its environment. Genetic drift describes evolution due to chance events and causes unpredictable fluctuations in allele frequencies. Genetic drift can have a particularly significant effect in a small population, such as during a bottleneck or founder event. Gene flow results when alleles are transferred into or out of a population due to the migration of fertile individuals or their gametes. Gene flow can bring new alleles (beneficial, harmful, or neutral) into a population.
Point mutations in noncoding regions of DNA result in __________.
Neutral Variation
The authors predicted an increase in toepad size and the number of lamellae on the toes of A. carolinensis lizards on invaded islands. The lizards use the toepads to grip the branches of bushes.
The evidence indicates that toepad size is genetically determined and that the change in toepad size was caused by natural selection.
The fruit fly Drosophila melanogaster has an allele that confers resistance to DDT and similar insecticides. Laboratory strains of D. melanogaster have been established from flies collected in the wild in the 1930s (before the widespread use of insecticides) and the 1960s (after 20 years of DDT use). Lab strains established in the 1930s have no alleles for DDT resistance. In lab strains established in the 1960s, the frequency of the DDT-resistance allele is 37%. Which statement is correct?
The evolutionary fitness associated with the heritable trait of DDT resistance changed once DDT use became widespread **As the environment changed with the increased use of DDT, the advantages of the heritable trait of DDT resistance increased. Natural selection has different effects in different environments.
What genotype frequencies are expected under Hardy-Weinberg equilibrium for a population with allele frequencies of p = 0.8 and q = 0.2 for a particular gene?
The expected frequency of the A1A1 genotype is p 2 = (0.8)(0.8) = 0.64; the expected frequency of the A1A2 genotype is 2pq = 2(0.8)(0.2) = 0.32; the expected frequency of the A2A2 genotype is q 2 = (0.2)(0.2) = 0.04. To verify your calculations, confirm that the three frequencies add up to one.
A storm separates a small number of birds in a migrating population. These birds end up at a destination different from where they usually migrate and establish a new population in this new area. This is an example of __________.
The founder effect
What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?
The founder effect is genetic drift attributable to colonization by a limited number of individuals from a parent population.
What is the frequency of the A1 allele in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?
The frequency of the A1 allele is p = (number of A1 alleles) / (total of all alleles) = [(2 ( 20) + 80] / [(2 × 20) + (2 × 80) + (2 × 100)] = 0.3.
How do lactase supplements help people who are lactose intolerant?
The supplements provide the enzyme that breaks down the lactose in dairy products.
Which statement correctly describes the role of chance in evolution?
The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA.
Your aunt conducts research on ocelots in Central America. Which of the following is true of her research subjects?
They have papillae on their tongues.
Consider a wildflower population with the following allele and genotype frequencies. Frequency of the CR allele: p = 0.6 Frequency of the CW allele: q = 0.4 Frequency of CRCR : 50% Frequency of CRCW : 20% Frequency of CWCW : 30%
To tell if this population is in Hardy-Weinberg equilibrium, you should calculate the expected genotype frequencies based on the allele frequencies. The frequency of genotype CRCR (red flowers) in the offspring generation is expected to be p 2 = (0.6)2 = 0.36. The frequency of genotype CRCW (pink flowers) is expected to be 2pq = 2(0.6)(0.4) = 0.48. The frequency of genotype CWCW (white flowers) in the offspring generation is expected to be q 2 = (0.4)2 = 0.16. Comparing these expected values with the actual genotype frequencies in the population, you can see that the frequency of genotype CRCW is too low while the frequencies of the other two genotypes are too high.
Lactose intolerance in infants is more common in the population today than it was a hundred years ago. Why?
Today there are alternatives to breast milk, such as lactose-free formula and soy milk, so lactose intolerant infants can survive.
In the Hardy-Weinberg equation, 2pq represents __________.
the expected frequency of the heterozygous genotype
In the Hardy-Weinberg equation, q2 represents __________.
the expected frequency of the homozygous recessive genotype