Prentice Hall Biology (California)
1st Edition
ISBN: 9780132013529
Textbook solutions
All Solutions
Page 413: Chapter 16 Assessment
Exercise 1
Solution 1
Solution 2
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A
Gene pool consists of all genes that are present in a population. It is the ultimate source of genetic information of all members in a population.
Result
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A
Step 1
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The collection of genetic information from all members of a population constitutes the **gene pool** of that population. The gene pool consists of genes and alleles of every member.
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When the allele frequencies of a population are altered, the gene pool is said to be altered as well. This results in changes in the frequency of traits and thus the population evolves.
Result
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A
Exercise 2
Solution 1
Solution 2
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A
This is major concept of evolution. Nature favors individuals that are best adapted or “fitted” to their environment.
Result
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A
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An organism that is very successful in surviving and reproducing in the context of its local environment is said to have a high degree of **fitness**, which pertains to being “well-suited”.
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If an organism is not able to adapt to its environment, then it has a low degree of fitness. This means that the organism is not likely to survive and reproduce in its local environment.
Result
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A
Exercise 3
Solution 1
Solution 2
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B
Poly- means many, and -genic means gene. So, traits controlled by many genes is called polygenic traits.
Result
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B
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Traits that are controlled by more than one gene, often with multiple alleles, are known as **polygenic traits**. Some examples of this type of trait are human height, eye color, and hair color.
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Since polygenic traits are controlled by multiple genes, they usually exhibit a continuous range of phenotypes rather than a few discrete phenotypes. This is represented by a bell curve.
Result
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B
Exercise 4
Solution 1
Solution 2
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B
In stabilizing selection, nature favors average trait and chooses against two extreme traits.
Result
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B
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There are three patterns of natural selection that can influence the frequency of phenotypes exhibited by polygenic traits. These are stabilizing, directional, and disruptive selection.
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The pattern of selection that favors the intermediate phenotype such as an average size is known as **stabilizing selection**. This results in a higher frequency of the average phenotype.
Result
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B
Exercise 5
Solution 1
Solution 2
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C
In directional selection, nature favors one end of the curve.
Result
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C
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Since polygenic traits exhibit a continuous range of phenotypes, it would exhibit two extreme phenotypes, one at each end of a curve. Certain patterns can affect the shape of this curve.
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The pattern of natural selection that favors either one of the extreme phenotypes (end of the curve) is known as **directional selection**. It increases the frequency of one extreme phenotype.
Result
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C
Exercise 6
Solution 1
Solution 2
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B
In disruptive selection, nature favors the middle of the curve while chooses against two ends of the curve. The graph changes from bell curve to “M” shape.
Result
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B
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As shown in the given graph, the two extreme phenotypes at each end of the curve are favored more than the average phenotype. This is a defining characteristic of **disruptive selection**.
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Disruptive selection occurs when both extreme phenotypes exhibit a higher degree of fitness than the intermediate phenotype. This may result in the formation of two distinct phenotypes.
Result
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B
Exercise 7
Solution 1
Solution 2
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Random changes in allele frequency of a small population just by chance is called genetic drift.
Result
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B
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Changes in the allele frequency of a population’s gene pool due to random chance is known as **genetic drift**. It is one of the forces that can drive the process of evolution in a population.
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It is also important to note that the effects of genetic drift are more pronounced in smaller populations. This is because genetic diversity is more likely to be lost in a smaller population.
Result
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B
Exercise 8
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The founder effect occurs when a small subgroup of a population decides to migrate from one place to another. As a result, there are now changes in their allele frequencies that are different from the original species.
Result
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C. the founder effect
Exercise 9
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Solution 3
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C. Population
A population is a group of the same species living in the same area, and if they live in the same area, then they can interbreed.
Result
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C. Population
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C
Group of individuals of the same species that interbreeds make up a population.
Result
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C
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A **population** is generally defined as a group of individuals from the same species that live in the same area, and are able to interbreed with each other and producing viable offspring.
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One defining characteristic of a population is that their gene pool is shared among its members. A different population would thus have a different gene pool among its own members.
Result
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C
Exercise 10
Solution 1
Solution 2
Step 1
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B
The finches are not artificially selected. Biologists found out that genes of the finches in different island are different, so they thought speciation has taken place.
Result
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B
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The evolution of Darwin’s finches resulted in the formation of new species of finches that are located in different geographical regions. Thus, the evolution of finches resulted in **speciation**.
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Speciation occurs when two or more populations of a species are isolated from each other. This may eventually cause the populations to become reproductively isolated from each other.
Result
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B
Exercise 11
Solution 1
Solution 2
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Relative frequency: The number of times an allele occurs in a gene pool compared with the number of times other allele occur.
Relative frequency (pg.394)
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Example sentence: Relative frequency is often expressed as a percentage.
Example use of relative frequency.
Result
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The work shows the definition of Relative frequency and and example sentence.
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**Relative frequency** is generally defined as the frequency (number of times) that an allele occurs in the gene pool of a population as compared to the frequency of the other alleles. The relative frequency of an allele is often expressed as a percentage.
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As an example, let’s say the allele *A* occurs 40 times in the gene pool of a population, while the allele *a* occurs 60 times. The relative frequency of allele *A* would be 40% while the relative frequency of allele *a* would be 60%, with respect to each other.
Exercise 12
Solution 1
Solution 2
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The sexual reproduction combines the genes in fresh way every time, creating genetic variation. In addition, crossing-over during meiosis can further increase genetic variation.
Result
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See explanation.
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Sexual reproduction involves the union of two gametes (i.e. sperm and egg). The production of these gametes involves a lot of genetic reshuffling that brings about genetic variation.
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For instance, the production of the gametes involves the process of meiosis. In this process, alleles are randomly segregated into each gamete. This brings about genetic variation.
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The process of meiosis also involves the crossing-over of genes in gametes. This further provides genetic variation, which is the reason why sexual reproduction is a source of variation.
Exercise 13
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The number of alleles assigned to a gene determines the number of phenotypes for a given trait. Single-gene trait with only 2 alleles for 1 gene result in 2 phenotypes. Polygenic trait with more than 2 alleles for 1 gene results in many phenotypes.
Result
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See explanation.
Exercise 14
Solution 1
Solution 2
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Single-gene trait means there are two alleles assigned to one gene, resulting in two distinct phenotypes.
Result
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See explanation.
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As its name suggests, a *single-gene trait* is a trait that is controlled by a single gene, usually with two alleles. This results in at most two distinct phenotypes that can be exhibited by the trait.
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The two distinct phenotypes of single-gene traits are often described as the presence or absence of a specific feature. Some examples include the widow’s peak and the hitchhiker’s thumb.
Exercise 15
Solution 1
Solution 2
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Since polygenic traits produce many different phenotypes due to a gene having two or more alleles assigned, the bell curve is effective to graph many phenotypes and their distribution.
Result
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See explanation.
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Polygenic traits are traits that are controlled by multiple genes, often with multiple types of alleles. This results in a continuous range of phenotypes rather than a few distinct phenotypes.
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Since polygenic traits exhibit a wide range of phenotypes, this can be best represented by a bell curve. This graph usually represents the frequency of each phenotype in a population.
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More often than not, intermediate phenotypes occur more frequently than extreme phenotypes. This is why polygenic traits often exhibit a bell-shaped curve when represented graphically.
Exercise 16
Solution 1
Solution 2
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Evolution is change in the relative frequency of alleles (frequency of one allele compare to frequency of other alleles of the same gene) in a gene pool of a population.
Result
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See explanation.
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In the context of genetics, evolution is defined as the changes in the allele frequencies in the gene pool of a population over time. This results in changes in the frequency of certain traits.
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The driving forces of evolution include mutations, genetic drift, gene flow, and nonrandom mating. These processes can alter the relative frequencies of alleles in a population’s gene pool.
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In contrast, the absence of these forces would result in a constant relative frequency of alleles. This means that the population is not evolving, but rather in Hardy-Weinberg equilibrium.
Exercise 17
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Solution 2
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Reproductive isolation occurs when members of two populations cannot interbreed and produce viable, fertile offspring anymore. This separates the gene pool, creating new species.
Result
2 of 2
See explanation.
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When two populations of a species are isolated from each other in certain aspects, they might evolve separately from one another. This could eventually result in reproductive isolation.
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Reproductive isolation occurs when two populations of a species cannot interbreed and produce viable and fertile offspring anymore. This results in the formation of two distinct species.
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Therefore, reproductive isolation may result in speciation. The isolation of two or more populations may cause them to evolve separately to the point where their genetic makeup does not allow them to interbreed and produce viable and fertile offspring.
Exercise 18
Solution 1
Solution 2
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Stabilizing selection occurs when nature favors average traits and disfavors two extreme traits. Disruptive selection occurs when nature favors two extreme traits and disfavors average traits. So, the two selections are completely different.
Result
2 of 2
See explanation.
Step 1
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Stabilizing selection and disruptive selection are different patterns of natural selection that can influence the frequency of phenotypes that are exhibited by polygenic traits in a population.
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In stabilizing selection, natural selection favors individuals with the intermediate phenotype of the polygenic trait. Individuals with any of the two extreme phenotypes are selected against.
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In disruptive selection, natural selection favors individuals with any of the two extreme phenotypes of the polygenic trait. Individuals with intermediate phenotypes are selected against.
Exercise 19
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. $textbf{Genetic equilibrium}$ is the situation in which population not evolving, and allele frequencies in a gene pool of population remain the same. It likely occurs when the population is very large, there is random mating, there are no mutations, there is no immigration/emigration, and there is no natural selection.
Result
2 of 2
Genetic equilibrium is the situation in which population not evolving, and allele frequencies in a gene pool of population remain the same. It likely occurs when the population is very large, there is random mating, there are no mutations, there is no immigration/emigration, and there is no natural selection.
Exercise 20
Solution 1
Solution 2
Step 1
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Genetic equilibrium occurs when allele frequency of a population is remained constant. The conditions are: large population size, no mutation, no gene flow, no natural selection, and random mating.
Result
2 of 2
See explanation.
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According to the Hardy-Weinberg principle, a population is said to be in genetic equilibrium (or Hardy-Weinberg equilibrium) when the relative allele frequencies in the population’s gene pool remain constant over time.
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In order for the relative allele frequencies to remain constant in a gene pool, the population must adhere to certain assumptions in the Hardy-Weinberg principle. These include specific conditions that are required to maintain genetic equilibrium.
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The conditions required to maintain genetic equilibrium include the absence of mutations, the absence of natural selection, the absence of gene flow (such as migrations), the absence of genetic drift, and the occurrence of random mating in a population.
Exercise 21
Solution 1
Solution 2
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Isolating the groups separates the gene pool and changes the relative frequency of alleles. This creates new species over a long period of time since the separate groups experience natural selection differently now.
Result
2 of 2
See explanation.
Step 1
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When two or more groups are isolated from each other, their gene pools are also separated. This means that each group will be acted upon separately by the processes of evolution.
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In other words, the isolated groups would be acted upon separately by natural selection. This would result in different changes in allele frequencies that lead to reproductive isolation.
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When reproductive isolation occurs, the two groups will not be able to interbreed and produce viable offspring. This would result in the formation of new species, known as speciation.
Exercise 22
Solution 1
Solution 2
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1: There must be enough heritable variations to create diverse birds’ beak sizes and shapes. 2: The differences in beak size and shape must produce differences in fitness which natural selection acts upon.
Result
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See explanation.
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Darwin’s hypothesis about the evolution of the Galapagos finches explains that natural selection acted upon the traits exhibited by the finches, which results in the evolution of species.
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Darwin’s hypothesis is based on two testable assumptions. One of them is that there must be heritable variation in the traits exhibited by the finches such as beak sizes and shapes.
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Another important assumption in Darwin’s hypothesis was that the variations in the traits of the finches should produce differences in fitness, which causes natural selection to occur.
Exercise 23
Solution 1
Solution 2
Result
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The couple spent years observing and documenting environmental conditions of Galapagos finches and how it related to beak structure. They discovered that environmental changes favored certain individuals who in turn, passed those favored traits on to their offspring. This occured more rapidly than previously supposed.
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According to Darwin’s theory on evolution, the Galapagos finches may have evolved through natural selection. This process acted on the variations of traits exhibited by the finches.
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For instance, the size and shape of the finches’ beaks are acted upon by natural selection in the context of their habitat. Those with beaks with the appropriate size and shape were able to eat the foods that are available in their habitat, thus having better chances at survival.
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On the other hand, finches that do not have the appropriate beak size and shape are less likely to survive and reproduce in their local habitat. Therefore, the frequencies of certain beak phenotypes will eventually change and the population of finches would evolve.
Exercise 24
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When the finches arrived in the different islands of Galápagos, they were isolated and they do not share the common gene pool anymore because they rarely flew over the open water. Even when some flew across from one island to another, their differences in mating rituals, ecological competition, and other behavioral patterns have made interbreeding and coexisting in one habitat difficult. Because of this, the gene pools of the two populations remained isolated. As a result, populations of finches in the different islands evolved separately and eventually, they have become separate species.
Overall, the evolution of the finches in the different islands of Galápagos occurred due to an interplay of several factors including the founding of new population, reproductive isolation, geographic isolation, changes in the new population’s gene pool, and ecological competition.
Result
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The evolution of the finches in the different islands of Galápagos occurred due to an interplay of several factors including the founding of new population, reproductive isolation, geographic isolation, changes in the new population’s gene pool, and ecological competition.
Exercise 25
Solution 1
Solution 2
Step 1
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6 millimeters. about 2 percent
Look at the purple graph for species A. The x-axis describes beak lengths y-axis describes percentage.
Result
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6 millimeters. about 2 percent
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As shown in the given graph, species A is represented by a purple line. Looking at this line, we can see that the shortest beak size that was observed in species A is about **6 millimeters**.
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Additionally, if we look at the percentage of birds observed (y-axis), we can see that the number of birds in species A that had beaks that are 6 millimeters in length is about **2 or 3 percent**.
Result
3 of 3
6 millimeters; about 2 or 3 percent
Exercise 26
Solution 1
Solution 2
Step 1
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9 millimeters, 14 millimeters, 22 millimeters
Look at the far right end of each graphs to determine the longest beak sizes.
Result
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9 millimeters, 14 millimeters, 22 millimeters
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As shown in the given graph, we can see that each of the species is represented by a color-coded line. The birds with the longest beaks are found at the right end of each colored line.
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As we can see in each line, species A (purple) has a longest beak size of about **9 millimeters**, species B (orange) has a longest beak size of about **14 millimeters**, and species C (blue) has a longest beak size of about **22 millimeters**.
Result
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Species A = 9 mm; species B = 14 mm; species C = 22 mm
Exercise 27
Solution 1
Solution 2
Step 1
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16 to 22 millimeters
Look at the blue graph from one end to the other end.
Result
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16 to 22 millimeters
Step 1
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As shown in the given graph, we can see that birds in species C are represented by a blue line. This line shows us the range of beak sizes that were observed in birds from species C.
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By looking at the x-axis, we can see that the blue line went across **16 millimeters** to **22 millimeters** in beak size. This is the interval or the range of beak sizes of species C.
Result
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16 mm to 22 mm
Exercise 28
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Species A that has smallest beak-size among others would probably eat soft, small seeds. Species C that has largest beak-size would probably eat hard, big seeds. Species B that has medium beak-size would probably eat medium size seeds.
Result
2 of 2
See explanation.
Exercise 29
Result
1 of 1
Due to the isolation of the smaller population among the original and larger population, a natural selection or a genetic drift may happen. If the smaller population could not adapt to their new environment, a natural selection will occur. Only those individuals with greater fitness would survive and reproduce. As a result, the remaining ones will pass down their traits and eventually, the new generation will have a different gene pool from the other group. On the contrary, a genetic drift may occur, which is only by chance, if the small population carries an allele that may reproduce more offspring than the other group. As a result, this kind of allele will become common in a particular population.
Exercise 30
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The Grants worked on Darwin’s hypothesis by using a medium ground finch on one of the islands in Galápagos. They have conducted an observation on the finches’ offspring, beak structure, feeding, and mating behavior. They have discovered that the size of the bird’s beak is related to the way it feeds itself and the way they mate with other birds. In addition, the birds with larger beaks have a higher chance of surviving when the vegetation is scarce during the hot and dry season. Eventually, finches born on the next generations have possessed larger beaks than the previous generation after the natural selection. According to the couple, evolution happened within just a span of a couple years. This opposed the notion of Darwin that evolution has occurred over thousands of years ago from a common ancestor.
Result
2 of 2
The Grants worked on Darwin’s hypothesis by using a medium ground finch on one of the islands in Galápagos. They have conducted an observation on the finches’ offspring, beak structure, feeding, and mating behavior. According to the couple, evolution happened within just a span of a couple years. This opposed the notion of Darwin that evolution has occurred over thousands of years ago from a common ancestor.
Exercise 31
Solution 1
Solution 2
Step 1
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It would force the individual to find a new sustainable food source, or to rely on its favorable traits, if any, to give it a fitness advantage. The species would have to rely on individuals within the population that have the ability or adaptation to use another food source to reshape the population otherwise the species will most likely die off.
Result
2 of 2
1
It would force the individual to find a new sustainable food source, or to rely on its favorable traits, if any, to give it a fitness advantage. The species would have to rely on individuals within the population that have the ability or adaptation to use another food source to reshape the population otherwise the species will most likely die off.
It would force the individual to find a new sustainable food source, or to rely on its favorable traits, if any, to give it a fitness advantage. The species would have to rely on individuals within the population that have the ability or adaptation to use another food source to reshape the population otherwise the species will most likely die off.
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For an individual organism, a limited resource would make them less likely to survive unless they can adapt. One way to do this is by taking advantage of new resources to survive.
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For an entire species, a limited resource would probably cause the species to die off unless they can also adapt. This means that individuals with favorable traits are likely to survive.
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Individuals with favorable traits, called adaptations, will be able to survive and reproduce better than those who do not. This can cause the population to spread the trait and evolve.
Exercise 32
Solution 1
Solution 2
Result
1 of 1
If the species were present with any form of isolation (geographical, temporal, behavioral) then the violets will evolve.
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The new species may have originated as a result of the reproductive isolation of two or more populations of violets. This phenomenon is most likely associated with temporal or behavioral isolation since the violets are all found in the same field (i.e. geographical location).
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What happened here is that two or more populations of violets were temporally or behaviorally isolated from each other. This prevents the sharing of their gene pools, which means that the driving forces of evolution would act upon them separately.
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Eventually, each isolated population would acquire enough variation to the point where they cannot interbreed and produce viable and fertile offspring anymore. At this point, the populations are said to be reproductively isolated, which leads to speciation.
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