When there is a well-established segment of heterochromatin on an inte

1.All the following statements about heterochromatin except:? It is a dark-staining area of a chromosome.;It is a region of condensed chromatin. ;It is usually transcriptionally active. ;It is often simple sequence DNA.;

2.All the following statements about heterochromatin except: 选项： A:It is a dark-staining area of a chromosome. ; B:It is usually transcriptionally active. ; C:It is often simple sequence DNA. ; D:It is a region of condensed chromatin.

3.The secret of immortality is hidden in a DNA sequence at the end of the chromosome. This sequence is called telomere. Scientists have confirmed that the cell's ability to divide is related to telomeres, and as the cells are dividing, the telomeres will ().选项： A:increase in length; B:shorten; C:keep the length ; D:decrease activity

4.What is the active transcriptional portion of chromatin in the interphase nucleus? 选项： A:Euchromatin; B:Heterochromatin; C:Extended chromatin ; D:Lamp chromatin

5.【单选题】Figure Q9-27 shows the nucleotide sequence from a protein-coding region of a gene in humans, chimpanzees, and gorillas and the protein sequence produced from this gene. The seventeen amino acids encoded by this DNA are numbered below. The two codons that are not conserved in all three species have been boxed. These two codons code for amino acids 3 and 15.Which of these statements is consistent with these sequence-comparison data? 选项： A:The gorilla sequence is more similar to the chimp sequence than to the human sequence. B:Since these sequences are so similar, this protein must also be found in invertebrates. C:The chimp DNA sequence has likely diverged at the DNA coding for amino acid 15 from the sequence found in the last common ancestor of humans and chimps. D:The last common ancestor of chimps and gorillas most likely used AAA to code for amino acid number 3.

6.单选题]Figure Q9-27 shows the nucleotide sequence from a protein-coding region of a gene in humans, chimpanzees, and gorillas and the protein sequence produced from this gene. The seventeen amino acids encoded by this DNA are numbered below. The two codons that are not conserved in all three species have been boxed. These two codons code for amino acids 3 and 15.Which of these statements is consistent with these sequence-comparison data? 选项： A:The gorilla sequence is more similar to the chimp sequence than to the human sequence. B:Since these sequences are so similar, this protein must also be found in invertebrates. C:The chimp DNA sequence has likely diverged at the DNA coding for amino acid 15 from the sequence found in the last common ancestor of humans and chimps. D:The last common ancestor of chimps and gorillas most likely used AAA to code for amino acid number 3.

7.Human nerve cells differ from human muscle cells because different sets of genes are expressed; in each type of cell, different genes are transcribed into mRNA and translated into protein. Which of the following techniques would be the most efficient way to identify the genes that these cells express?选项： A: gel electrophoresis of DNA fragments; B:DNA microarray assays; C:isolating and analyzing all the proteins from each type of tissue; D:PCR

8.Genes located in which region of a eukaryotic chromosome are most likely to be transcribed? 选项： A、centromere B、telomere C、euchromatin D、heterochromatin

9.In addition to producing protein, the gene or DNA can also be manipulated and introduced into cells or organisms to study its function through recombinant DNA technology.

10.Choose the molecular definition of a gene that includes all of DNA
elements that may be part of the DNA sequence of a gene: ( ) 选项： A、The DNA sequence of a gene includes only exons. B、The DNA sequence of a gene includes only exons and introns. C、The DNA sequence of a gene includes exons, introns and noncoding
regulatory control regions. D、The DNA sequence of a gene includes exons, introns, noncoding
regulatory control regions and intergenic regions.

11.Which of the following statements about differentiated cells is true 选项： A、Cells of distinct types express nonoverlapping sets of transcription factors. B、Once a cell has differentiated, it can no longer change its gene expression. C、Once a cell has differentiated, it will no longer need to transcribe RNA. D、Some of the proteins found in differentiated cells are found in all cells of a multicellular organism.

12.Interphase chromosomes are a mixture of highly compact heterochromatin and less compact euchromatin 选项：A、正确B、错误

13.What distinguishes stem cells from other cell types?选项： A:Although all cell types can divide, only stem cells differentiate after division.; B:Stem cells are able to divide to produce populations of cells that differentiate into a related set of cells.; C:Stem cells divide asymmetrically to give rise to one daughter cell that remains a stem cell, and a second daughter cell that differentiates into one or more cell types.; D:Stem cells have a special type of cell division in which they form small stems that then pinch off to give rise to the daughter cell.

14.What distinguishes stem cells from other cell types? 选项： A、Although all cell types can divide, only stem cells differentiate after division. B、Stem cells are able to divide to produce populations of cells that differentiate into a related set of cells. C、Stem cells divide asymmetrically to give rise to one daughter cell that remains a stem cell, and a second daughter cell that differentiates into one or more cell types. D、Stem cells have a special type of cell division in which they form small stems that then pinch off to give rise to the daughter cell.

15.A 15-year-old boy was diagnosed with skin cancer. He had always been sensitive to sunlight, and had remained indoors for most of his life. An analysis of his DNA, from isolated fibroblasts, indicated an increased level of thymine dimers when the cells were exposed to UV light. The boy developed a skin tumor owing to an increased mutation rate, which was caused by which one of the following? 选项： A:A lack of DNA primase activity B:Decreased recombination during mitosis C:Increased recombination during mitosis D:Loss of base excision repair activity E:Loss of nucleotide excision repair activity

16.What is “Retreat” about? 选项： A:.Take the children in trouble away from the situation, no matter what happened; B:This technique can be used when a child is using aggressive behavior that may hurtthemselves or others; C:It is intended to remove the child from a situation when the child has been warned of theaggressive behavior and explained that it is not acceptable behavior. D:It is the best way of protecting children

17.What is the best evidence that genes encode the amino acid sequence of proteins? 选项： A、Proteins are macromolecules B、The amino acid of polypeptide is changed by gene mutation C、DNA serves as a template for RNA D、mRNA is found in the ribosome

18.If two genes from a parent cell are on the same chromosome, which of the following best explains why the daughter cells may not have the same alleles as the parent for both genes?

19.Which of the following is not true of the nucleus ( )? 选项： A:Skeletal muscle cells have many nuclei.; B: DNA is kept in the nucleus.; C:All eukaryotic cells have just one nucleus.; D:Nuclei vary in appearance according to cell type and organism.; E:Heterochromatin is relatively decondensed.

20.A Barr body is a(n):选项： A:gene on the X chromosome that is responsible for female development.; B:patch of cells that has a phenotype different from surrounding cells because of variable X inactivation; C: inactivated X chromosome, visible in the nucleus of a cell that is from a female mammal.; D:extra X chromosome in a cell that is the result of nondisjunction.; E:extra Y chromosome in a cell that is the result of nondisjunction.