Term
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Definition
| Bacteria and other prokaryotes are cells much __ and more __ organized than those of eukaryotes, such as plants and animals |
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Definition
| Lacking the __ and __ machinery found in cells, most viruses are little more than genes packaged in protein coats |
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Definition
| Viruses are capable of causing a wide variety of __ and can be spread between organisms |
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Definition
| Viruses can not reproduce or carry out metabolic function outside of a __ cell |
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Definition
| Experiments with viruses provided important evidence that genes are made of __, and they were critical in working out the __ mechanisms of the fundamental processes of DNA replication, transcription, and translation |
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Definition
| __ disease stunts the growth of tobacco plants and gives their leaves a mottles, or mosaic, coloration |
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Definition
| In 1883 Mayer discovered he could transmit the disease from plant to plant by rubbing sap extracted from diseased leaves onto healthy plants. Mayer suggested that the disease was caused by unusually small __ that were invisible under a microscope |
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Definition
| Mayer’s hypothesis was tested a decade later by Ivanowsky. Ivanowsky passed sap from infected tobacco leaves through a filter designed to remove bacteria. But the sap still produced mosaic disease. He reasoned the bacteria were __ enough to pass through the filter or made a __ that could do so |
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Definition
| Beijerinck carried out a classic series of experiments that showed that the infectious agent in the filtered sap could reproduce and that the pathogen reproduced only within the host it infected. Through experiments Beijerinck showed that the mysterious agent of mosaic disease could not be __. He imagined a reproducing particle much smaller and simpler than a bacterium |
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Definition
| Beijerinck is credited with being the first scientist to voice the concept of a __ |
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Definition
| Stanely confirmed Beijerinck’s thoughts when he __ the infectious particle |
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Definition
| The tiniest viruses are only 20nm in diameter – smaller than a __ |
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Definition
| Viruses are infectious particles consisting of nucleic acid enclosed in a __ and, in some cases, a membranous envelope |
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Definition
| Virus __ may consist of double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA |
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Definition
| A virus is called a DNA virus or an RNA virus, according to the kind of __ that makes up its genome |
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Term
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Definition
| The genome of a virus is usually organized as a __ linear or circular molecule of nucleic acid, although the genomes of some viruses consist of multiple molecules of nucleic acid |
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Term
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Definition
| __ genomes contain about 200 to a few thousand genes |
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Definition
| __ – the protein shell enclosing the viral genome |
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Definition
| The type of virus determines the capsid __ |
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Definition
| Capsids are built from a large number of protein subunits called __ |
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Definition
| Rod-shaped viruses are commonly called __ viruses |
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Definition
| Adenoviruses, which infect the respiratory tracts of animals are __ viruses |
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Term
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Definition
| Some viruses have accessory structures that help them __ their hosts (ex: membranous envelope) |
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Definition
| __ – derived from the membranes of the host cell. They contain host cell phospholipids and membrane proteins. They contain proteins and glycoproteins of viral origin |
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Definition
| __ are proteins with carbohydrates covalently attached |
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Definition
| Many of the most complex capsids are found among the viruses that infect bacteria, called __, or simply phages |
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Definition
| Viruses lack metabolic enzymes and equipment for making __, such as ribosomes |
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Definition
| Viruses can only reproduce only within a __ |
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Term
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Definition
| Viruses in __ are just packaged set of genes in transit from one host cell to another |
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Term
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Definition
| Each type of virus can infect cells of only a limited variety of hosts, called the __ of the virus |
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Term
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Definition
| Viral infection begins when a virus __to a host cell and the viral genome makes its way inside |
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Term
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Definition
| The mechanism of genome entry depends on the __ of virus and the type of host cell |
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Definition
| Once the viral genome is inside, the proteins it encodes can commandeer the host, reprogramming the cell to copy the viral __ and manufacture viral __ |
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Term
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Definition
| The __ provides the nucleotides for making viral nucleic acids, as well as enzymes, ribosomes, tRNAs, amino acids, ATP, and other components needed for making the viral proteins |
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Term
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Definition
| Most DNA viruses use the DNA __ of the host cell to synthesize new genomes along the templates provided by the viral DNA |
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Definition
| To replicate their genomes, RNA viruses use __ polymerases that can use RNA as a template (healthy cells make no enzymes for carrying out this process) |
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Term
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Definition
| After the viral nucleic acid molecules and capsomeres are produced, they spontaneously self-assemble into new __ |
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Definition
| The simplest type of viral reproductive cycle ends with the exit of hundreds or thousands of viruses from the infected host cell, a process that often __ or __ the cell |
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Term
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Definition
| Such cellular damage and death, as well as the body’s responses to this destruction, cause many of the __ associated with viral infections |
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Term
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Definition
| The viral progency that exit a cell have the potential to infect additional cells, spreading the __ |
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Term
| Phages (bacterial viruses) |
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Definition
| __ are the best understood of all viruses |
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Term
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Definition
| Research on phages led to the discovery that some double-stranded DNA viruses can reproduce by two alternative mechanisms: the __ cycle and the __ cycle |
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Term
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Definition
| A phage reproductive cycle that culminates in death of the host cell is known as a __ |
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Term
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Definition
| During the last stage of infection, the bacterium lyses (breaks open) and __ the phages that were produced within the cell |
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Term
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Definition
| A phage that reproduces only by a lytic cycle is a __ phage |
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Term
| 1. attachment, 2. entry of phage DNA and degradation of host DNA, 3. synthesis of viral genomes and proteins, 4. assembly, 5. release |
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Definition
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Term
1. natural selection favors bacterial mutants with receptors that are no longer recognized by a particular type of phage.
2. when phage DNA successfully enters a bacterium, the DNA often is identified as foreign and cut up by cellular enzymes called restriction enzymes |
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Definition
| how come phages haven’t exterminated all bacteria? |
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Term
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Definition
| __ – their activity restricts the ability of the phage to infect the bacterium |
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Term
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Definition
| __ also favors phage mutants that can bind the altered receptors or are resistant to particular restriction enzymes |
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Term
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Definition
| the parasite-host relationship is in __ evolutionary flux |
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Term
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Definition
| another reason bacteria are not extinct is because many phages coexist with them in a state called __ |
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Term
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Definition
| __ – allows replication of the phage genome without destroying the host |
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Term
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Definition
| Phages capable of using both modes or reproducing within a bacterium are called __ phages |
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Term
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Definition
| A temperate phage called __, is widely used in biological research. It resembles T4, but its tail has only one, short tail fiber |
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Term
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Definition
| During a __ cycle, the viral genes immediately turn the host cell into a λ-producing factory, and the cell soon lyses and releases its viral products |
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Term
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Definition
| During a __ cycle, the λ DNA molecule is incorporated into a specific site on the E. coli chromosome by viral proteins that break both circular DNA molecules and join them to each other |
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Term
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Definition
| during a lysogenic cycle, the viral DNA molecule is incorporated into a specific site on the host chromosome by viral proteins that break both circular DNA molecules and join them to each other. when integrated into the bacterial chromosome in this way, the viral DNA is known as a __ |
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Term
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Definition
| One prophage gene codes for a protein that __ transcription of most of the other prophage genes |
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Term
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Definition
| after a bacterium has undergone a lysogenic cycle with a viral molecule, A single infected cell can quickly give rise to a __ population of bacteria carrying the virus in prophage form |
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Term
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Definition
| Lysogenic implies that prophages are capable of generating active phages that __ their host cells |
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Term
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Definition
| An __ signal usually triggers the switchover from the lysogenic to the lytic mode |
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Term
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Definition
| In addition to the gene for the transcription-preventing protein, a few other prophage genes may be __ during lysogeny |
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Term
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Definition
| Expression of prophage genes may alter the host’s __ |
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Term
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Definition
| Many variations on the basic scheme of viral infection and reproduction are represented among the __ viruses. One key variable is the nature of the viral genome |
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Term
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Definition
| The nature of the genome is the basis for the common __ of viruses |
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Term
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Definition
| Single stranded RNA viruses are further classified into __ classes according to how the RNA genome functions in a host cell |
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Term
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Definition
| Whereas few bacteriophages have an envelope or RNA genome, many animal viruses have __ |
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Term
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Definition
| Nearly all animal viruses with RNA genomes have an __, as do some DNA genomes |
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Term
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Definition
| An animal virus equipped with an envelope – an outer membrane – uses it to __ the host cell |
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Term
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Definition
| Protruding from the outer surface of this envelope are viral __ that bind to specific receptor molecules on the surface of a host cell |
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Term
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Definition
| The protein parts of envelope glycoproteins are made by ribosomes bound to the endoplasmic reticulum (ER) of the __ cell; cellular enzymes in the ER and Golgi apparatus then add the sugars |
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Term
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Definition
| The resulting viral glycoproteins, embedded in host cell-derived membrane, are transported to the cell __ |
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Term
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Definition
| New viral capsids are wrapped in __ as they bud from the cell (much like exocytosis) |
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Term
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Definition
| The viral envelope is derived from the host cell’s __, although some of the molecules of this membrane are specified by viral genes |
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Term
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Definition
| Some viruses have envelopes that __ derived from plasma membrane |
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Term
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Definition
| The broadest variety of RNA genomes is found among the viruses that infect __ |
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Term
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Definition
| Among the three types of single-stranded RNA genomes found in animal viruses, the genome of class IV viruses can directly serve as __ and thus can be translated into viral protein immediately after infection |
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Term
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Definition
| In viruses of class V, the RNA genome serves as a template for mRNA __. The RNA genome is transcribed into complementary RNA strands, which function both as mRNA and as templates for the synthesis of additional copies of genomic RNA |
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Term
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Definition
| All viruses that require RNA → RNA synthesis to make mRNA use a viral __ capable of carrying out this process; there are no such enzymes in most cells |
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Term
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Definition
| The viral enzyme is packaged with the genome inside the viral __ |
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Term
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Definition
| The RNA animal viruses with the most complicated reproductive cycles are the __ (class VI) |
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Term
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Definition
| Retroviruses are equipped with an enzyme called __, which transcribes an RNA template into DNA, providing an RNA → DNA information flow, the opposite of the usual direction |
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Term
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Definition
| Although viruses cannot reproduce or carry out metabolic functions independently, their use of the __ makes it hard to deny their evolutionary connection in the living world |
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Term
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Definition
| Viruses have been found that infect every form of __ |
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Term
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Definition
| Because they depend on cells for their own propagation, viruses evolved __ the first cells appeared, possibly multiple times |
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Term
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Definition
| Most molecular biologists favor the hypothesis that viruses originated from naked bits of __ that moved from one cell to another, perhaps via injured cell surfaces |
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Term
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Definition
| Candidates for the original sources of viral genomes include __ and __ |
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Term
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Definition
| __ are small, circular DNA molecules found in bacteria and in the unicellular eukaryotes called yeast. they exist apart from the cell’s genome, can replicate independently of the genome, and are occasionally transferred between cells |
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Term
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Definition
| __ are DNA segments that can move from one location to another within a cell’s genome |
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Term
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Definition
| Plasmids, transposons, and viruses all share an important feature: they are __ genetic elements |
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Term
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Definition
| a viral genome can have __ in common with the genome of its host than with the genomes of viruses that infect other hosts |
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Term
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Definition
| Some viral genes are essentially identical to genes of the host, on the other hand, recent sequencing of many viral genomes has shown that the genetic sequences of some viruses are quite similar to those of seemingly distantly related __ |
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Term
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Definition
| __ – largest virus yet discovered. It is a double-stranded DNA virus with an icosahedral capsid that is 400 nm in diameter. Its genome contain 1.2 million bases and an estimated 1,000 genes |
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Term
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Definition
| Viruses may damage or kill cells by causing the release of __ enzymes from lysosomes |
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Term
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Definition
| Some viruses cause infected cells to produce __ that lead to disease symptoms, and some have molecular components that are toxic, such as envelope proteins |
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Term
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Definition
| How much damage a virus causes depends partly on the ability of the infected tissue to __ by cell division |
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Term
| defending itself against infection |
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Definition
| Many of the temporary symptoms associated with viral infections actually result from the body’s own efforts at __ rather than from cell death caused by the virus |
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Term
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Definition
| A __is a harmless variant or derivative of a pathogen that stimulates the immune system to mount defenses against the harmful pathogen |
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Term
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Definition
| Viruses that appear suddenly or are new to medical scientists are often referred to as __viruses |
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Term
| 1. mutation of existing viruses, 2. dissemination of a viral disease from a small, isolated human population, 3. spread of existing viruses from other animals |
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Definition
| what three processes contribute to the emergence of viral diseases? |
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Term
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Definition
| descent with modification, a phrase Darwin used in proposing that Earth’s many species are descendents of ancestral species that were different from the present-day species |
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Term
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Definition
| – a change in the genetic composition of a population from generation to generation |
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Term
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Definition
| Evolution is a pattern and a process. The __ of evolutionary change is revealed by data from a range of scientific disciplines, including biology, geology, physics, and chemistry. These data facts are then observed about the natural world. The __ of evolution consists of the mechanisms that produce the observed pattern of change |
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Term
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Definition
| Aristotle recognized certain “affinities” among organisms. He concluded that life-forms could be arranged on a ladder, or scale, of increasing complexity, later called the __ (“scale of nature”). |
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Term
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Definition
| Linnaeus sought to classify life’s diversity, in his words, “for the greater glory of God.” He developed a __, system of naming species that is still used today. |
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Term
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Definition
| Darwin drew many of his ideas from the work of scientists studying __, the remains or traces of organisms from the past |
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Term
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Definition
| New layers of sediment cover older ones and compress them into superimposed layers of rock called __ |
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Term
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Definition
| __ – the study of fossils. Developed by Cuvier |
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Term
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Definition
| Cuvier noticed that the older the stratum, the more dissimilar its fossils were to current life-forms. From one layer to the next, new species appeared while others disappeared. Cuvier opposed the idea of evolution and to explain his ideas, he advocated __, the principle that events in the past occurred suddenly and were caused by mechanisms different from those operating in the present. Cuvier though that each boundary between strata represented a catastrophes that had destroyed many of the species living at that time and that they were confined to local regions, which were later repopulated by species immigrating from other areas |
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Term
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Definition
| __ proposed that Earth’s geologic features could be explained by gradual mechanisms still operating |
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Term
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Definition
| Lyell incorporated Hutton’s thinking into his principle of __, which stated that mechanisms of change are constant over time. Lyell proposed that the same geologic processes are operating today as in the past, and at the same rate |
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Term
1. Use and disuse – the idea that parts of the body that are used extensively become larger and stronger, while those that are not used deteriorate.
2. Inheritance of acquired characteristics – stated that an organism could pass these modifications to its offspring |
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Definition
| Lamarck published his hypothesis in 1809. By comparing living species with fossil forms, Lamarck had found what appeared to be several lines of descent, each a chronological series of older to younger fossils leading to a living species. He explained his findings with what two principles: |
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Term
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Definition
| During the voyage on the Beagle, Darwin observed many examples of __, characteristics of organisms that enhance their survival and reproduction in specific environments |
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Term
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Definition
| Darwin’s explanation of how adaptations arise centered on __, a process in which individuals with certain inherited traits leave more offspring than individuals with other traits |
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Term
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Definition
| Darwin reasoned that over long periods of time, descent with modification eventually led to the rich _ of life we see today |
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Term
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Definition
| Humans have modified other species over many generations by selecting and breeding individuals that possess desired traits – a process called __ |
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Term
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Definition
| Darwin perceived an important connection between natural selection and the capacity of organisms to __ |
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Term
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Definition
| Natural selection is a process in which individuals that have certain heritable characteristics survive and reproduce at a higher rate than other __ |
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Term
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Definition
| •Over time, natural selection can increase the match between organisms and their __ |
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Term
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Definition
| If an environment changes, of if individuals move to a new environment, natural selection may result in adaptation to these new conditions, sometimes giving rise to new __ in the process |
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Term
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Definition
| individuals do not evolve. Rather, it is the __ that evolves over time |
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Term
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Definition
| Natural selection can amplify or diminish only __ – traits that are passed from organisms to their offspring |
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Term
| direct observations of evolution, the fossil record, homology, and biogeography |
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Definition
| Four types of data that document the pattern of evolution and illuminate the processes by which it occurs: |
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Term
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Definition
| A second type of evidence for evolution comes from __. its record shows that past organisms differed from present-day organisms and that many species have become extinct. They also show the evolutionary changes that have occurred over time in various groups of organisms |
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Term
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Definition
| A third type of evidence for evolution comes from analyzing __ among different organisms |
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Term
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Definition
| __ – similarity resulting from common ancestry |
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Term
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Definition
| Some homologous characteristics, such as __, are shared by all species because they date to the deep ancestral past. In contrast, homologous characteristics that evolved more recently are shared only within __ groups of organisms |
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Term
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Definition
| a diagram that reflects evolutionary relationships among groups of organisms. they are hypotheses that summarize our current understanding of patterns of descent. Our confidence in these relationships, as with any hypothesis, depends on the strength of the supporting data |
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Term
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Definition
| Although organisms that are closely related share characteristics because of common descent, distantly related organism can resemble one another for a different reason: __, the independent evolution of similar features in different lineages |
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Term
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Definition
| Fourth type of evidence for evolution comes from __, the geographic distribution of species. The geographic distribution of species is influenced by many factors including continental drift, the slow movement of Earth’s continents over time |
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Term
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Definition
| evolution on its smallest scale, called microevolution, as change in__ frequencies in a population over generations |
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Term
| natural selection, genetic drift, and gene flow |
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Definition
| what are the three main mechanisms that can cause allele frequency to change |
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Term
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Definition
| natural selection could not cause evolutionary change unless individuals __ in their inherited characteristics |
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Term
| Mutation and sexual reproduction |
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Definition
| __ and __ are two processes that produce genetic differences |
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Term
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Definition
| Each person has a unique genotype, reflected in individual __ variations |
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Term
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Definition
| Some phenotypic variation __ heritable |
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Term
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Definition
| Characters that vary within a population may be _ or _ |
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Term
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Definition
| __ characters, such as the purple or white flower colors of Mendel’s pea plants, can be classified as an either-or basis (each plant has flowers that are either purple or white) |
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Term
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Definition
| Many discrete characters are determined by a single __ with different alleles that produce distinct phenotypes |
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Term
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Definition
| Most heritable variation involves quantitative characters, which vary along a __ within a population |
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Term
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Definition
| Heritable quantitative variation usually results from the influence of __ genes on a single phenotypic character |
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Term
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Definition
| Gene variability can be quantified as the __, the average percent of loci that are heterozygous (two different alleles for a given locus, whereas a homozygous individual has two identical alleles for that locus) |
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Term
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Definition
| nucleotide variability is measured by comparing the DNA sequences of __ individuals in a population and then averaging the data from many such comparisons |
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Term
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Definition
| gene variability (that is, average heterozygosity) tends to be __ than nucleotide variability. This is because a gene can consist of thousands of nucleotides and a difference at only one of these nucleotides can be sufficient to make two alleles of that gene different which increases gene variability |
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Term
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Definition
| •In addition to variation observed within a population, species also exhibit __ variation, differences in the genetic of separate populations |
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Term
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Definition
| The ultimate source of new alleles is __, a change in the nucleotide sequence of an organism’s DNA |
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Term
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Definition
| In multicellular organisms, only mutations in cell lines that produce __ can be passed on to the offspring |
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Term
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Definition
| A change of as little as one base in a gene – a “__ mutation” – can have significant impact on phenotype |
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Term
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Definition
| Chromosomal changes that delete, disrupt, or rearrange many loci at once are almost certain to be harmful. But when such large-scale mutations leave genes intact, their effects on organisms may be __ |
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Term
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Definition
| Mutation rates tend to be __ in plants and animals. mutation rates in prokaryotes are __ than plants and animals because of the life span |
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Term
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Definition
| In organisms that reproduce __, most of the genetic variation in a population results from the unique combination of alleles that each individual receives |
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Term
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Definition
| It is the mechanism of sexual reproduction that shuffles the existing alleles and deals them at __ to determine individual genotypes |
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Term
| crossing over, independent assortment of chromosomes, and fertilization |
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Definition
| Three mechanisms contribute to this shuffling: |
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Term
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Definition
| __ – a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring |
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Term
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Definition
| We can characterize a populations genetic makeup by describing its __, which consists of all the alleles for all the loci in all individuals of the population |
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Term
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Definition
| If only one allele exists for a particular locus in a population, that allele is said to be fixed in the gene pool, and all individuals are __ for that allele |
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Term
| homozygous or heterozygous |
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Definition
| If there are two or more alleles for a particular locus in a population, individuals may be either __ or __ |
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Term
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Definition
| Each allele has a __ (proportion) in the population |
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Term
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Definition
| For loci that have more than two alleles, the sum of all allele frequencies must still equal __ |
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Term
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Definition
| __ – states that the frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work |
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Term
| 1. no mutations, 2. random mating, 3. no natural selection, 4. extremely large population size, 5. no gene flow |
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Definition
| Conditions for Hardy-Weinberg Equilibrium? |
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Term
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Definition
| New __ can alter allele frequencies, but because mutations are rare, the change from one generation to the next is likely to be very small |
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Term
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Definition
| Nonrandom mating can affect the frequencies of homozygous and heterozygous genotypes but by itself usually has no effect on allele frequencies in the __ |
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Term
| natural selection, genetic drift, and gene flow |
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Definition
| The three mechanisms that alter allele frequencies directly and cause most evolutionary change are __ |
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Term
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Definition
| __ selection is based on differential success in survival and reproduction: individuals in a population exhibit variations in their heritable traits, and those with traits that are better suited to their environment tend to produce more offspring than those with traits that are less well suited |
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Term
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Definition
| Chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next, especially in small populations – a process called __ |
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Term
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Definition
| When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool differs from the source population |
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Term
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Definition
| A sudden change in the environment, such as a fire or flood, may drastically reduce the size of the population. A severe drop in population size can cause the __, so named because the population has passed through a restrictive “bottleneck” in size |
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Term
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Definition
| Genetic drift is significant in __ populations |
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Term
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Definition
| Genetic drift can cause allele frequencies to change at __ |
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Term
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Definition
| Genetic drift can lead to a loss of genetic __ within populations |
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Term
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Definition
| Genetic drift can cause harmful alleles to become __ |
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Term
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Definition
| Allele frequencies can also change by __, the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes |
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Term
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Definition
| gene flow tends to __ the genetic differences between populations |
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Term
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Definition
| Gene flow, like mutation, can introduce new alleles into a population. But because it can occur at a higher rate than mutation, gene flow is __ likely than mutation to alter allele frequencies directly |
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Term
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Definition
| only natural selection consistently increases the frequencies of alleles that provide reproductive advantage and thus leads to __ evolution |
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Term
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Definition
| Adaptive advantage can lead to greater __: the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals |
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Term
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Definition
| Selection acts __ directly on the phenotype than on the genotype; its acts on the genotype indirectly, via how the genotype affects the phenotype |
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Term
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Definition
| __ selection occurs when conditions favor individuals exhibiting one extreme of a phenotypic range, thereby shifting the frequency curve for the phenotypic character in one direction or the other |
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Term
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Definition
| _ selection occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes |
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Term
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Definition
| __ selection acts against both extreme phenotypes and favors intermediate variants. This mode of selection reduces variation and tends to maintain the status quo for a particular phenotypic character |
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Term
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Definition
| Adaptations can arise gradually over time as natural selection increases the frequencies of alleles that enhance survival and reproduction. As the portion of individuals that have favorable traits increases, the match between a species and its __ improves; that is, adaptive evolution occurs |
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Term
| 1. selection can act only of existing variations, 2. evolution is limited by historical constraints, 3. adaptations are often compromises, 4. chance, natural selection, and the environment interact |
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Definition
| why can't natural selection fashion perfect organisms |
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Term
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Definition
| the process by which one species splits into two or more species |
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