Biology Test

Assume that a species needs a fairly long neck to reach its food. How might Hox genes contribute to the evolution of this species?

A mutation in the Hox genes that control the development of neck length could cause longer or shorter necks. An organism with a longer neck might be able to get food more efficiently. Therefore, the organism might survive better to become a new species.

Define mutation and describe one situation in which a mutation changes an organism's phenotype in a way that affects fitness and another situation in which a mutation would not affect an organism's fitness.

A mutation is any change in the genetic material of a cell. Some mutations reduce an organism's ability to survive, such as an insect with a tongue that is too short to eat its usual amount of food. A mutation that is neutral has no effect on the organism's phenotype and therefore no effect on fitness.

What is the principle of common descent?

According to the principle of common descent, all species- living and extinct- are descended from ancient common ancestors.

What are the major steps that were likely involved in the speciation of the Galápagos finches?

According to this hypothesis, speciation in finches occurred by founding of a new population, geographic isolation, changes in the new population's gene pool, behavioral isolation, and ecological competition.

For a trait that has many different alleles, would an individual in the population be more likely to have that allele if it has a low allele frequency or a high allele frequency? Why?

An individual would be more likely to have an allele with a high allele frequency. A high frequency indicates that the allele occurs at a higher percentage, or more often, than do alleles with a low allele frequency.

For a population, are the frequencies of phenotypes for a single-gene trait best expressed by a bar graph or a curve? Are the frequencies of phenotypes for a polygenic trait best expressed by a bar graph or a curve? Explain.

Bar graph, because there are only two or three distinct phenotypes. Polygenic would require a curve, because the symmetrical bell-like shape of this curve is typical of polygenic traits and one polygenic trait can have many possible phenotypes.

Why might a geographic barrier such as a large river cause the formation of a new species of small rodents but not a new species of birds?

Because while birds could still travel, a species of rodents would be isolated. A large river would likely keep populations of small rodents apart, but it would not necessarily isolate birds and other populations that can fly.

Adaptations can be physical traits or they can be behaviors. Give an example of an organism with each type of adaptation, and explain how the adaptation affects the organism's fitness.

Body parts or structures: a tiger's claws; colors (mimicry or camouflage): scarlet king snake has the colors of a venomous eastern coral snake; physiological functions: plants carry out photosynthesis; behavioral: crane's defensive stance.

How was Darwin's concept of natural selection influenced by the practices of English farmers?

Darwin called this process artificial selection. In artificial selection, nature provides the variations, and humans select those they find useful. Darwin realized that factors in the environment could act in a comparable way, "selecting" the organisms that would die early and those that would survive and pass their traits to the next generation.

Summarize Charles Darwin's contribution to science.

Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors.

What was Charles Darwin's contribution to science, and how did he develop it?

Darwin developed a scientific theory of biological evolution that explains how modern organisms over long periods of time through descent from common ancestors. He noticed that different, yet ecologically similar, animal species inhabited separated, yet ecologically similar, habitats around the globe. Additionally, he noticed that different, yet related, animal species often occupied different habitats within a local area. Finally, he noted that some fossils of extinct animals were similar to living species. He explained that species change over time through natural selection: the survival and reproduction of those members of a population that are best suited to their environment.

Darwin observed that different animals that lived in similar habitats existed around the world. Give an example of animals that Darwin observed that supported this observation.

Darwin found flightless, ground-dwelling birds called rheas living in the grasslands of South America. Rheas look and act like ostriches, yet they only live in South America, and ostriches only in Africa. When Darwin visited Australia's grasslands, he found another large flightless bird, the emu.

What sources of evidence contributed to Charles Darwin's presentation of his concept of evolution by natural selection?

Darwin found the research of Hutton and Lyell, Lamarck, Malthus, and breeders. From Hutton and Lyell, he learned that Earth is old that the processes that changed it in the past are the same that operate it in the present. Lamarck suggested that organisms could change during their lifetimes by selectively using/ not using various parts of their bodies, and individuals could pass these acquired traits on to their offspring. Malthus reasoned that if the human population grew unchecked, there wouldn't be enough living space and food for everyone, and the plant and animal breeders use artificial selection. Darwin considered the fossil record, the geographic distribution of living species, the evidence of homologous body structures, and similarities in embryological development of vertebrates.

What did Charles Darwin observe about some of the fossils he collected during his voyage on the Beagle and living species found in the same areas?

Darwin noticed that some of the fossils were similar to living species.

How did Thomas Malthus's ideas about human population growth inspire Darwin's thinking about evolution?

Darwin realized that Malthus's reasoning applied even more to other organisms than it did to humans. When Darwin realized that most organisms don't survive and reproduce, he wondered which individuals survive, and why.

Describe one way that new genes can evolve.

During meiosis, a chromosome may acquire a duplicate gene. If a mutation occurs in the duplicate gene, that mutation might cause a change in the function of the duplicate gene. If the gene affects the phenotype of the organism, natural selection could act on the population.

How did the farmers observed by Charles Darwin take advantage of natural variation to improve their livestock?

Farmers would select for breeding only trees that produced the largest fruit or cows that produced the most milk. Over time, this selective breeding would produce more trees with even bigger fruit and cows that gave even more milk.

How can small changes in Hox genes can cause large changes in organisms?

How genes can turn other genes on or off during embryological development. A change in the activity of one Hox gene can affect how an entire segment of an organism is patterned. For example, whether the segment has legs or wings, and how big or small those legs or wings will be.

Summarize the contribution to science made by Hutton and Lyell.

Hutton and Lyell concluded that Earth is extremely old and that the processes that changed Earth in the past are the same processes that operate in the present.

Is an allele for a trait that has no effect on a species' fitness affected by natural selection? Explain.

If a trait has no effect on fitness, the allele that produces it will not be under pressure from natural selection.

What might happen if a well-adapted population experienced sudden major changes in its environment?

If local environment conditions change, some traits that were once adaptive mat no longer be useful, and different traits may become adaptive. And if environmental conditions change faster than a species can adapt to those changes, the species may become extinct.

How does artificial selection differ from natural selection?

In artificial selection, nature provides the variations, and humans select those they find useful. In natural selection, the environment- not a farmer or animal breeder- influences fitness.

How does the size of a population relate to genetic drift?

In small populations, individuals that carry a particular allele may leave more descendants than other individuals leave, just by chance. Over time, a series of chance occurrences can cause an allele to become more or less common in a population. Generally, the smaller a population is, the easier it is for allele frequencies to change. Genetic drift occurs when the allele frequencies in small populations change by chance.

What can be concluded from the similarity in the Hox genes that control limb development in many types of organisms?

In vertebrates, sets of homologous Hox genes direct the growth of front and hind limbs. Small changes in these genes can produce dramatic changes in the structures they control. At least some Hox genes are found in almost all multicellular animals, from fruit flies to humans. Living organisms evolved through descent with modification from a common ancestor. The similarity of Hox genes in many types of organisms is evidence that the organisms all evolved from a common ancestor.

The Hardy-Weinberg principle describes the conditions that can change the frequency of alleles in a population. Explain how that change occurs.

It makes predictions like Punnett Squares, but for populations through (1) nonrandom mating, since secual selection can change gene frequency, (2) when there is immigration or emigration to add or remove genes, and (3) when natural selection favors a particular phenotype.

Summarize Thomas Malthus's ideas about population growth.

Malthus reasoned that if the human population grew unchecked, there wouldn't be enough living space and food for everyone.

If each of the Galápagos Islands had contained an identical assortment and abundance of vegetation, would the impact of natural selection have been as pronounced as it was? Explain.

No, because there would have been less competition, which would have lessened the need for species deviation, as everyone would have food to eat. Evolution probably would not have progressed as quickly as it did because selection pressures would have been lower under those circumstances.

Suppose a plant breeder selectively breeds a plant for its bright red flower and creates a new population with little variation. Would the new population survive if it were released into the wild? Explain.

No, because without adaptations, the flowers would be unable to endure the conditions of the wild. In both artificial and natural selection, only certain individuals in a population produce new individuals.

What are three mechanisms for reproductive isolation? Which mechanism isolates two populations of similar frogs with different mating calls?

Reproductive isolation can develop in a variety of ways, including behavioral isolation, geographic isolation, and temporal isolation. Behavioural isolation occurs when two populations that are capable of interbreeding develop differences in courtship rituals or other behaviors. Two populations of frogs that are isolated due to difference mating calls is an example of behavioral isolation.

Assume that a single population becomes split by migration across a geographic barrier that divides two very different ecosystems, as is shown in Figure 17-8. What would likely happen to the two separated populations? Would this process occur more quickly, less quickly, or at the same rate as it would if the two populations lived in similar ecosystems?

Separate gene pools form, causing genetic changes in each individual group. Speciation would tend to occur more quickly in two groups in different ecosystems than is similar ecosystems because in different ecosystems, the groups would experience different selection pressures. Those selection pressures would drive the evolution of the two populations in different directions, speeding up the process of speciation.

Would a trait that has only two distinct phenotypes more likely be a single-gene trait or a polygenic trait? How do you know?

Single-gene traits may have just two or three distinct phenotypes.

What might happen when a Hox gene turns other genes on or off?

Small changes can make a big difference in organisms. If a Hox gene turns off a gene for wings in an insect larva, the adult insect will probably not have wings.

What might explain the differences in the mutations of the species in Figure 17-4?

Species C may share an older common ancestor with both Species A and B. The longer a species has been evolving independently, the more differences there are likely to be in the gene pool of those species.

List the five conditions that can disturb genetic equilibrium in a population.

The Hardy-Weinberg principle predicts that five conditions can disturb genetic equilibrium and cause evolution to occur: (1) nonrandom mating; (2) small population size; and (3) immigration or emigration; (4) mutations; or (5) natural selection.

Explain how you could calculate the allele frequency of an allele in a gene pool.

The allele frequency of an allele is the number of times the allele occurs in the gene pool divided by (or compared with) the total number of alleles for the same gene.

What did the Grants discover about Galápagos finches?

The data the Grants have recorded show that there is indeed great variation of heritable traits among finches. Individual finches with different beak sizes have better or worse changes of surviving both seasonal droughts and longer dry spells. Their word shows that variation within a species increases the likelihood of the species' adapting to and surviving environmental change. The Grants documented changes in the finch population consistent with Darwin's ideas of natural selection.

How can gene duplication affect evolution?

The duplicate might acquire a mutation. If the mutation is positive, it will be selected for by natural selection to become more frequent in the population.

How is the idea of common descent supported by examples of homologous structures as shown in Figure 16-5?

The similar structures in the bones suggest that birds and humans have a common ancestor. Homologous bones support the differing hands/ ends of the structures. If these animals had no common ancestor, there wouldn't be such similar structures.

Describe the founder effect, and describe the conditions in which it arises.

The situation in which allele frequencies change as a result of the migration of a small subgroup of a population is known as the founder effect. This subgroup may carry alleles in different frequencies than does the larger population from which it came. The founder effect arises from genetic drift- a change in the frequencies due to chance rather than normal selection.

What did Charles Darwin learn about how the land tortoises of the Galápagos Islands varied from island to island?

The tortoises varied from island to island in predictable ways, such as shell shape and neck length. The variations seemed to enable the tortoises to exploit food resources on the islands.

What was the scientific value of the specimens that Charles Darwin brought back to England?

The trip lead Darwin to develop what has been called the single best idea anyone has ever had. His specimens helped him form his theory of evolution by natural selection.

How many differences are there in the DNA of the three species in Figure 17-4? What could be learned by comparing those differences?

There are two differences in Dna between A and B, and three differences in DNA between A and C or B and C. You can infer that A and B share a more recent common ancestor than A and C or B and C.

Why are neutral mutations useful for molecular clocks?

They don't affect an organism's phenotype. A neutral mutation would likely occur at about the same rate in different species, letting researchers compare the DNA using a molecular clock. Students may point out that mutations that have a large positive or negative effect on an organism's phenotype are very much affected by natural selection and too variable for molecular clocks.

Many modern whales have a vestigial pelvis and femur, such as is shown in Figure 16-1. What does this evidence suggest about ancestors of modern whales?

This could suggest whales once walked on land. A femur plays a big part in the motion of legs.

What are the three main sources of genetic variation within a population? Which is most common among eukaryotes?

Three sources of genetic variation are mutation, genetic recombination during sexual reproduction, and lateral gene transfer. Most of the time, in more eukaryotic organisms, genes are passed only from parents to offspring (during sexual or asexual reproduction.).

What does the continued presence of vestigial structures like the whale pelvis and femur shown in Figure 16-1 suggest about the impact vestigial structures have on fitness?

Vestigial structures have little to no effect on fitness, and, therefore, natural selection does not act to eliminate it. If there were a disadvantage, then the structures would be selected against and you'd expect them to no longer be present.

Explain how the finches and tortoises that Charles Darwin observed on the Galápagos Islands influenced his thinking.

When Darwin first saw the finches, he thought they were wrens, warblers, and black-birds because they looked so different from one another. Once Darwin learned that the birds were all finches, he hypothesized that they had descended from a common ancestor. Galapagos turtles' differing shells told Darwin that different, yet related, animal species often occupied different habitats within a local area.

Are the members of a population necessarily the same species? Explain.

Yes, because a population is a group of individuals of the same species that mate and produce offspring.