A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of _____.- a change in a developmental gene or its regulation that altered the spatial organization of body partsAccording to the biological species concept, for speciation to occur, _____.- at least one gene, affecting at least one phenotypic trait, must changeThe common ancestors of birds and mammals were very early (stem) reptiles, which almost certainly possessed three-chambered hearts (two atria, one ventricle). Birds and mammals, however, are alike in having four-chambered hearts (two atria, two ventricles). The four-chambered hearts ofbirds and mammals are best described as _____.- Homoplasies (character shared by species, but not in their common ancestor)Which value(s) would be required to calculate how long ago the most recent ancestor of ungulates lived?I) the number of base pairs that differ among species in a certain genetic sequenceII) the total number of base pairs in the genetic sequence examinedIII) the age of a fossil ancestor for calibration- All threeWhich of the following is the correct sequence of events in the origin of life?I. formation of protobiontsII. synthesis of organic monomersIII. synthesis of organic polymersIV. formation of DNA-based genetic systems- II, III, I, IVHow were conditions on the early Earth of more than three billion years ago different from those on today's Earth? Unlike Earth today, early Earth _____.- had an atmosphere rich in gases released from volcanic eruptions ?Which of the following would be LEAST likely in the fossil record?- Dessert-dwelling speciesAccording to the concept of punctuated equilibrium, _____.- a new species accumulates most of its unique features as it comes into existenceAccording to the punctuated equilibria model,- most new species accumulate their unique features relatively rapidlyas they come into existence, then change little for the rest of their duration as a species.Which characteristic was NOT advantageous for organisms in the million years after the catastrophic asteroid impact?- Large body sizeThe various taxonomic levels (for example, phyla, genera, classes) of the hierarchical classification system differ from each other on the basis of _____.- Their inclusivenessLinnaeus believed that species remained fixed in the form in which they had been created. Linnaeus would have been uncomfortable with _____.- PhylogeniesWhich of the following statements best describes the rationale for applying the principle of parsimony in constructing phylogenetic trees?- Similarity due to common ancestry should be more common than similarity due to convergent evolution.The reason that paralogous genes can diverge from each other within the same gene pool, whereas orthologous genes diverge only after gene poolsare isolated from each other, is that _____.- having an extra copy of a gene permits modifications to the copy without loss of the original gene productMolecular clocks are based on the idea that _____.- on average neutral mutations arise at a constant rateWhy do some scientists believe that RNA, rather than DNA, was the first genetic material?- RNA has both information storage and catalytic properties.One hypothesis that has been proposed regarding the origin of life suggests that life evolved from an "RNA world" to todays "DNA world." Considering the properties of RNA and DNA molecules, which questionswould direct an investigation of the most insightful test(s) of this hypothesis?- Could RNA have provided a template for DNA assembly, thereby enabling a more stable molecule that is replicated more accurately?The atmosphere of early Earth probably contained no O2 until the emergence of organisms that _____.- used water as an electron source for photosynthesisWhat is thought to be the correct sequence of these events, from earliest to most recent, in the evolution of life on Earth?1. origin of mitochondria2. origin of multicellular eukaryotes3. origin of chloroplasts4. origin of cyanobacteria5. origin of fungal-plant symbioses- 4, 1, 3, 2, 5Which of the following was derived from an ancestral cyanobacterium?- ChloroplastAn early consequence of the release of oxygen gas by plant and bacterial photosynthesis was to _____.- cause iron in ocean water and terrestrial rocks to rust (oxidize)The oxygen revolution changed Earth's environment dramatically. Which ofthe following took advantage of the presence of free oxygen in the oceans and atmosphere?- the evolution of cellular respiration, which used oxygen to help harvest energy from organic moleculesThe K-T boundary is a layer of debris ranging from large chunks of fractured rock to thin clay deposits and it is found in many different parts of the world. It separates rock layers from the end of the Cretaceous period from those beginning of the Tertiary period. It coincides with an abrupt loss of biodiversity.How do foraminifera found in rock layers above the K-T boundary compareto those in rock layers below?- Foraminifera above the boundary are smaller and less diverse than those below.Iridium is a component of cosmic dust that rains down upon the earth at a constant rate. Why did Luis Alvarez suggest measuring iridium levels in theK-T boundary?- He was looking for a way to determine how quickly the layer had been deposited.Asteroid impact hypothesis: The energy from an iridium-rich asteroid impact melted and transformed rock and ejected the material at varying distances from the impact site. Altered rock forms like shocked quartz, spherules and tektites were important clues in the search for the impact crater.- In the lytic cycle, virus parts are made, new viruses are assembled, and the cell is lysed, releasing the newly assembled viruses.- In the lysogenic cycle, the viral DNA incorporates into the bacterial DNA and is passed on to daughter bacterial cells when the infected bacteria reproduce normally.Nonenveloped viruses (a) typically exit the host cell by bursting through the plasma membrane.Enveloped viruses (b) generally escape from the host cell by budding. Because of this, the viral envelope is often derived from the host cell's plasma membrane.HIV) is a retrovirus that contains two copies of its RNA genome and two copies of reverse transcriptase. The HIV viral envelope facilitates binding to a white blood cell. After HIV enters the cell, the