mastering 16 – Flashcards
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What is a nondisjunction?
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An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell
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When can nondisjunction occur? Choose the best answer.
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Nondisjunction errors can occur in meiosis I, when homologous chromosomes fail to separate, or in either mitosis or meiosis II, when sister chromatids fail to separate.
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Which syndrome is characterized by the XO chromosome abnormality?
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Turner syndrome is characterized by a chromosome pattern of XO, or one X chromosome and no Y chromosome.
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What kind of cell results when a diploid and a haploid gamete fuse during fertilization?
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A triploid cell has three sets of chromosomes: the two from the diploid gamete and the one from the haploid gamete.
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Of the following chromosomal abnormalities, which type is most likely to be viable in humans?
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Some trisomies are viable in humans, but they result in developmental abnormalities, such as Down syndrome (trisomy 21). Only humans with trisomies of the small chromosomes (13, 18, or 21) or the sex chromosomes survive past birth.
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If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?
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A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.
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If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?
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A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.
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What is a telomere?
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the ends of linear chromosomes
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In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?
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DNA polymerase III
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Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1 ?
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aneuploidy
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Which of the following is true of DNA during interphase?
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It exists as chromatin and is less condensed than mitotic chromosomes.
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What results if a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction?
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an inversion
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The leading and the lagging strands differ in that _____.
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the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction
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What is meant by the description "antiparallel" regarding the strands that make up DNA?
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The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.
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What is the function of topoisomerase?
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relieving strain in the DNA ahead of the replication fork
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In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.
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thymine ... cytosine
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After DNA replication is completed, _____.
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each new DNA double helix consists of one old DNA strand and one new DNA strand
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The first step in the replication of DNA is catalyzed by _____.
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helicase
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The action of helicase creates _____.
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replication forks and replication bubbles
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Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?
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DNA polymerase can assemble DNA only in the 5' to 3' direction
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The synthesis of a new strand begins with the synthesis of a(n) _____.
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RNA primer complementary to a preexisting DNA strand
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An old DNA strand is used as a _____ for the assembly of a new DNA strand.
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template
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One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?
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translocation
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If cell X enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, what will be the result at the completion of meiosis?
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1/4 of the gametes descended from cell X will be n + 1, 1/4 will be n - 1, and 1/2 will be n.
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What is the function of helicase in DNA replication?
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It untwists the double helix and separates the two DNA strands.
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How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?
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It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.
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What is a major difference between eukaryotic DNA replication and prokaryotic DNA replication?
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Prokaryotic chromosomes have a single origin of replication, while eukaryotic chromosomes have multiple origins of replication.
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Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following?
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gaps left at the 5' end of the lagging strand
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What provides the energy for the polymerization reactions in DNA synthesis?
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the deoxyribonucleotide triphosphate substrates
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Short segments of newly synthesized DNA are joined into a continuous strand by _____.
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ligase
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Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?
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DNA polymerase can assemble DNA only in the 5' to 3' direction
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The synthesis of a new strand begins with the synthesis of a(n) _____.
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RNA primer complementary to a preexisting DNA strand
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If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?
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A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.
