Evolution Making Sense of Life 2nd Edition By Carl Zimmer - Test Bank

Evolution Making Sense of Life 2nd Edition By Carl Zimmer – Test Bank

 

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Test Bank, Chapter 5

1. Most chemical reactions in a cell are performed by:

• DNA
• RNA
• Protein
• Amino acids

2. A mature RNA transcript differs from a primary RNA transcript because:

• Exons are spliced out of the mature transcript
• Introns are spliced out of the mature transcript
• Exons are added to the mature transcript
• Introns are added to the mature transcript

3. The presence of a mRNA transcript of a gene in a cell means:

• Translation of the gene has occurred
• Transcription of the gene has occurred
• A and b are correct
• None of the above

4. Which of the following statements is correct:

• All cells have the same genes
• All cells express the same genes
• All cells have the same proteins
• All are correct

5. Which of the following statements is correct:

• microRNAs bind DNA and block transcription
• microRNAs bind mRNA and block translation
• microRNAs bind ribosomal RNA and block translation
• All of the above

6. Organisms vary considerably in genome size. Which of the following explains most of this variation:

• Differences in the number of protein coding genes
• Differences in the number ribosomal RNA genes
• Differences in the number of pseudogenes
• Differences in the number of mobile genetic elements

7. You are studying crickets and notice that individuals have one of two distinctive wing phenotypes (short-winged or long-winged). From this, you can confidently conclude:

• Long and short-winged crickets have different alleles at a locus controlling wing size
• Only one genetic locus contributes to the wing phenotype
• The trait must be polyphenic
• All of the above
• None of the above

8. You are studying snails and find that individuals have shells that either coil to the right or the left. Which of the following is/are the most plausible explanation(s) for this variation?

• Different alleles at a single locus produce the different phenotypes
• Individuals are genetically identical but certain environmental conditions trigger the production of each coil type
• This is a quantitative trait meaning that many loci contribute to the phenotypic differences
• A and b are correct
• All are correct

9. Polyphenic traits are an example of:

• phenotypic plasticity
• quantitative trait loci
• simple genetic polymorphism
• Dominant traits

10. Horizontal gene transfer:

• can occur via the transfer of plasmids
• can be beneficial to the organism
• is more common in eukaryotes than prokaryotes
• a and b are correct
• all are correct

11. DNA methylation:

• is a form of transcriptional regulation of gene expression
• is a form of post-translational regulation of gene expression
• is a form of post-transcriptional regulation of gene expression
• None of the above

12. Which of the following is involved in pre-transcriptional gene regulation:

• Histones
• MicroRNA
• DNA methylation
• Alternative splicing

13. Trans-acting regulatory elements:

• are typically adjacent to genes they regulate
• are typically far away from genes they regulate
• include transcription factors
• a and c are correct
• b and c are correct

14. Why are mutations crucial for evolution?

Mutations are the ultimate source of genetic variation in populations.  Mechanisms of evolution require genetic variation as the basis for evolutionary change.

15. One way mutations can affect the phenotype is by altering the coding sequence of a gene and therefore changing protein structure. Please describe two ways that mutations can affect the phenotype that does not include alteration of the protein coding sequence.

Mutations can occur in cis- or trans-acting elements.  These elements influence where, when, and how much of  a gene is transcribed.  Thus, while the resulting protein structure may be unchanged, a difference in regulation can alter the phenotype. 

16. Michael Lynch and his colleagues demonstrated in yeast that mutations occur rarely—in fact a single yeast cell may not experience a single point mutation in its genome. How can we reconcile the low rate of mutation with the fact that mutation is the engine that drives evolution?

Although the likelihood of any mutation in a given  individual occurring is low, a population of many individuals is likely to produce many new mutations each generation.  This is the raw material for evolution, which is a process that occurs at the level of the population, not the individual.

17. Discuss the importance of somatic and germ-line mutations for evolution.

Somatic mutations, even though they can affect fitness, are not heritable and thus not particularly important for evolution.  Germ-line mutations can be passed from parent to offspring and thus produce genetic variation on which evolutionary processes can act.

18. Each of us is genetically unique. Describe two processes that ensure that your future full sibling is going to be genetically different from you, even though you have the same parents.

Independent assortment: during meiosis independent assortment ensures that every gamete will be a mixture of maternal and paternal chromosomes.

Recombination: recombination results when homologous chromosomes break and rejoin during meiosis.  This shuffles around alleles, and, coupled with independent assortment, ensures gametes are genetically unique.

19. Height is a quantitative trait meaning that genes at several loci contribute to the phenotype. Does this mean that any two individuals in a population that differ in height also differ in the alleles they carry?

Not necessarily.  Quantitative traits are also influenced by the environment.  Theoretically two individuals could have exactly the same genotype but have a different phenotype due to environmental influences. 

20. Compare and contrast how genetic variation is created in eukaryotes vs. bacteria and archaea.

Similarities: Genetic variation in eukaryotes and bacteria/archaea can arise through the process of mutation.  

Differences: Eukaryotes that reproduce sexually experience recombination and independent assortment.  While this does not create “new” alleles, these processes do reshuffle alleles to ensure that no two individuals are identical.  Bacteria/archaea do not perform meiosis and thus do not experience recombination and independent assortment.

Bacteria/archaea commonly experience horizontal gene transfer.  While this can occur in eukaryotes, it seems to occur much less frequently.

21. Please describe one reason diploid organisms may benefit from having two copies of every gene.

A deleterious allele can be masked by the presence of a functional copy.

22. Describe one reason histone proteins are important in cells.

DNA in eukaryotic cells is wound tightly around histone proteins.  One reason this is important is that it allows DNA to fit into the nucleus—without the coiling it would be way too long.  Histones are also important because depending on how DNA is wrapped around histone proteins, certain genes may be inaccessible for processing.

23. Please critique the following statement: a single gene codes for a single protein.

This is not necessarily true.  If a gene has multiple exons these can be spliced together in different ways to create different proteins. 

24. Transcription factors and hormones can both influence gene expression. Describe how they differ.

Transcription factors are proteins produced within the cell bind to regulatory regions of DNA, thereby influencing gene expression.  Hormones, on the other hand, are signals that move from cell to cell.  When reaching their destination they may bind to receptors that then send signals that may alter patterns of gene expression.

25. Please give an example of how genes are regulated at each of the following stages:

Pre-transcription: coiling or packing of DNA making it more or less accessible to processing

Transcription: DNA can be methylated, which blocks transcription.

Post-transcription: Alternative splicing can lead to the production of different proteins

Translation: Binding of regulatory proteins or microRNAs can influence whether translation occurs

Post-translation: Cleavage or amino acid chains, binding of other proteins, etc. can alter the structure and/or function of  a protein