6.8 Biotechnology

1. AThe length of the fragment, from how far it moves in a gel
   A student who thinks DNA sequencing is the same as running a gel picks this. A gel shows a fragment's approximate length from how far it travels; sequencing gives the order of its nucleotides.
2. BThe order of the amino acids that make up the fragment
   A student who thinks DNA contains amino acids picks this. A DNA fragment is made of nucleotides; amino acids make up proteins.
3. CThe order of the nucleotides along the fragment Correct
   DNA sequencing determines the order of nucleotides in a DNA molecule. Sequences from different samples can then be compared.
4. DThe sequence of every gene in the plant's genome
   A student who thinks a DNA technique reads the whole genome picks this. Sequencing this fragment gives the sequence of this fragment only.

CED 6.8.A.1.iv · Read this in Fix

1. ALane 1's fragments are longer, as longer fragments carry more charge and are pulled farther
   A student who thinks longer fragments travel farther because they carry more charge picks this. Charge rises with length, but so does the drag of the gel; shorter fragments travel farther.
2. BLane 1's fragments are shorter, as shorter fragments move through the gel more easily Correct
   DNA is negatively charged, so all the fragments moved from the wells toward the positive electrode. The gel slows longer fragments more, so in the same time shorter fragments travel farther. Lane 1's band traveled much farther, so its fragments are shorter.
3. CLane 2's fragments are positive, as they stayed near the negative electrode
   A student who thinks DNA is positively charged picks this. Both samples moved away from the wells toward the positive electrode; DNA's phosphate groups give it a negative charge. Lane 2's fragments moved less because they are longer.
4. DThe two lanes' fragments differ in base sequence, which sets how far each moves
   A student who thinks gel electrophoresis separates DNA by sequence picks this. Fragments are separated by size and charge; two fragments of the same length move about the same distance whatever their sequences.

CED 6.8.A.1.i · Read this in Fix

1. AThe DNA in E could have come from person 2, who shares three of the four bands in E
   A student who treats the person sharing the most bands as the source picks this. A sample can come from a person only if every band matches; person 2 lacks E's band at position 7 and has a band at position 4 that E lacks.
2. BThe DNA in E could have come from person 3, as brothers have the same DNA
   A student who thinks siblings have identical DNA picks this. Person 3's pattern shares only two of E's bands; siblings inherit different combinations of their parents' chromosomes, as the different patterns of persons 1 and 3 show.
3. CThe DNA in E could have come from person 1, whose bands match all of E's bands Correct
   Person 1's pattern matches E's at every band (positions 1, 3, 5 and 7), so E's DNA could have come from person 1. Person 2 lacks E's band at position 7 and person 3 lacks E's bands at positions 3 and 7, so neither could be the source.
4. DNo conclusion is possible, as a fingerprint must compare whole genomes
   A student who thinks a DNA fingerprint compares every gene picks this. A fingerprint compares a few highly variable regions, which is enough to tell individuals apart.

CED 6.8.A.1.iv · Read this in Fix

1. A96 copies Correct
   Each cycle doubles the number of copies, because every strand, new or old, is a template in the next cycle. After 5 cycles: 3 × 2⁵ = 3 × 32 = 96 copies.
2. B18 copies
   A student who thinks only the original molecules are copied picks this: 3 new copies per cycle for 5 cycles, 3 + 15 = 18. New copies are also templates, so the number doubles each cycle.
3. C30 copies
   A student who multiplies by 2 × n instead of 2ⁿ picks this: 3 × 2 × 5 = 30. Doubling five times multiplies by 2 × 2 × 2 × 2 × 2 = 32.
4. D32 copies
   A student who takes 2ⁿ as the number of copies whatever the starting number picks this: 2⁵ = 32. That is the number from one starting molecule; with 3 it is 3 × 32 = 96.

Working Each cycle, every strand serves as a template, so the number of double-stranded copies doubles. After n cycles, copies = starting number × 2ⁿ = 3 × 2⁵ = 3 × 32 = 96. Distractors: only the 3 original molecules copied each cycle, 3 + 5 × 3 = 18; multiplying by 2 × n, 3 × 2 × 5 = 30; 2ⁿ alone, 2⁵ = 32.

CED 6.8.A.1.ii · Read this in Fix

1. ABonds within each strand break, which splits the DNA into single nucleotides
   A student who thinks heating breaks DNA into nucleotides picks this. Denaturing breaks only the hydrogen bonds between the strands; each strand stays intact so that it can be copied.
2. BDNA polymerase copies each strand, as enzymes work fastest at the hottest step
   A student who thinks enzymes work faster the hotter it is picks this. An enzyme's rate rises with temperature only up to its optimum; at the hottest step the strands separate, and DNA polymerase extends the primers in a later, cooler step.
3. CHeat activates the primers, which then act as enzymes that copy each strand
   A student who thinks primers are enzymes picks this. Primers are short strands that bind to the templates after the strands have separated; DNA polymerase, not the primers, builds the new strands.
4. DHydrogen bonds between the paired bases break, so the two strands separate Correct
   Step Q is held at the highest temperature, about 95 °C: the denaturing step. Heat breaks the hydrogen bonds between paired bases, so the double-stranded DNA separates into single strands that can serve as templates. DNA polymerase extends primers in a later, cooler step.

CED 6.8.A.1.ii · Read this in Fix

1. APlate 2, which differs from plate 1 only in having no plasmid added Correct
   Plate 2 has the same bacteria on the same medium with antibiotic A, but no plasmid. If cells grow on plate 1 and not on plate 2, the growth on the antibiotic results from the plasmid: the plasmid transformed some cells and gave them resistance.
2. BPlate 4, which has the plasmid but no antibiotic A in its medium
   A student who thinks the control is always the setup with the test condition removed picks this. Plate 4 shows that the treated cells are alive, but both transformed and untransformed cells grow without the antibiotic, so it cannot show the plasmid's effect.
3. CPlate 3, which has antibiotic A in its medium but no bacteria
   A student who thinks a control is a setup with nothing in it picks this. Plate 3 shows only that the medium is not contaminated; it lacks bacteria, so it cannot show what the plasmid does.
4. DPlate 5, which differs from plate 1 in both plasmid and antibiotic
   A student who thinks a control that differs in more factors gives a clearer comparison picks this. With two factors changed, any difference from plate 1 could come from either.

CED 6.8.A.1.iii · Read this in Fix

1. AThe plasmid carried the human polypeptide itself, which the bacteria took up
   A student who thinks DNA contains the proteins it codes for picks this. A plasmid is DNA; the bacteria made the polypeptide by expressing the gene.
2. BTransformation changed the bacteria into human-like cells able to make human proteins
   A student who reads 'transformation' as a change of form picks this. The bacteria took up foreign DNA and remain bacteria; they make the polypeptide because they share the genetic code.
3. CThe plasmid DNA built the polypeptide directly, without being transcribed or translated
   A student who thinks DNA makes proteins directly picks this. The gene was transcribed into mRNA and translated by the bacteria's ribosomes.
4. DBacteria and humans share the genetic code, so the gene's codons specify the same amino acids Correct
   The genetic code is shared by almost all organisms, so the bacteria's RNA polymerase and ribosomes transcribe and translate the human gene, and each codon specifies the same amino acid as in human cells. The result supports the universality of the genetic code.

CED 6.8.A.1.iii · Read this in Fix

1. AAmplify the gene by PCR, then use gel electrophoresis to find the order of its nucleotides
   A student who thinks gel electrophoresis reveals a DNA sequence picks this. A gel separates fragments by size and charge; it cannot give the order of nucleotides.
2. BAmplify the gene by PCR, then use DNA sequencing to find the order of its nucleotides Correct
   The sample is too small to analyze directly, so PCR first amplifies the chosen gene, using primers that bind to its ends. DNA sequencing then determines the order of nucleotides in the copies, which can be compared with the gene's sequence in living birds.
3. CUse PCR to copy the bird's whole genome, then compare every one of its genes at once
   A student who thinks PCR copies the whole genome picks this. PCR amplifies only the region between its primers, here the chosen gene.
4. DUse PCR to build the gene from nucleotides and primers alone, as the sample is too small
   A student who thinks DNA polymerase can make DNA without a template picks this. Each new strand is copied from a template strand; without the bird's DNA, nothing would specify the gene's sequence.

CED 6.8.A.1 · Read this in Fix

1. AEvery region of the DNA is amplified, as no primers limit the copying
   A student who thinks PCR copies all the DNA in a sample picks this. Primers are needed to start copying; without them, no region is amplified.
2. BThe gene is not amplified, as no primers anneal to start the new strands Correct
   DNA polymerase can add nucleotides only to an existing strand. In PCR, primers anneal to the separated template strands at each end of the gene and are extended. Without primers, no new strands are started, so the gene is not amplified.
3. CThe gene is amplified as usual, as polymerase builds DNA from nucleotides alone
   A student who thinks DNA polymerase can make DNA without a template and primer picks this. Polymerase only extends a primer that is paired with a template strand.
4. DThe DNA stays double-stranded when heated, as primers are what separate it
   A student who thinks primers are enzymes that separate strands picks this. Heat separates the strands in the denaturing step whether or not primers are present.

CED 6.8.A.1.ii · Read this in Fix