Molecular Genetics Chapter 4 Smartworks

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Each of the following statements about conserved and nonconserved regions in a comparison of mouse and human genomes is true EXCEPT:

Nonconserved regions include sequences with critical but undefined functions.

Roughly half of the DNA in the human genome consists of repeated sequences.

True

What is the term for the evolutionary process that eliminates individuals carrying mutations that interfere with important genetic functions?

Purifying selection

To complete the table, what number should be written in place of the question marks for the comparison of fish and whale?

17

Are all of the exons of the human β-globin gene (indicated by shading in Part A) homologous to the mouse β-globin gene? How would you explain any discrepancies if present?

No, the discrepancies are bits that do not encode protein.

Assuming that substitutions occurred at the same rate in the duplicated sequences generated by these Alu insertions, how long ago did this group of Alu sequences insert into these genes?

14 million years

Multispecies sequence comparisons have revealed large numbers of so-called multispecies conserved sequences, the majority of which code for proteins.

False

Which one of the following statements correctly describes what has been learned in studies of chromosomal sequences that have been conserved during mammalian evolution but have been deleted from the human genome in the six million years since humans and chimpanzees diverged?

They reveal changes in sequences that are thought to regulate brain development.

  1. Reception of extracellular signals 2. Post-translational protein modification 3. Development and transcription regulation

In which order did these major regulatory innovations occur during vertebrate evolution, from earliest to latest?

3-1-2

What is the basis for the variable intensity of hybridization of RsaI-A genes in males with normal color vision?

The duplicated genes can recombine due to their sequence similarity to generate more copies.

What is the term for a copy of a functional gene that has become irreversibly inactivated by multiple mutations?

Pseudogene

About 500 million years ago, the original globin gene was duplicated and mutated to form two slightly different genes encoding proteins that could form a hemoglobin molecule containing two α and two β chains (see the figure). Why is this event considered such an important evolutionary advance?

Hemoglobin releases oxygen more efficiently in the tissues.

How does the presence of long introns affect such duplication events?

Long introns increase the probability of favorable duplication events, because duplication can occur by recombination at many potential sites rather than just a few sites.

Which one of the following orders correctly ranks the rate—from fastest to slowest—at which deleterious, advantageous, and neutral mutations would be expected to spread through a population?

Advantageous–neutral–deleterious

How many single nucleotide differences do you suppose would be found in a comparison of the genomes from two unrelated individuals?

Millions of nucleotide pairs

Which one of the following statements correctly characterizes a property of the variants discovered by comparing the genome sequences from many individuals?

Most common variants were fixed long ago, in ancient times.

From which, if any, of the individuals did the drop of blood at the crime scene originate?

Individual B

Each of the following changes to the genome is likely to cause genetic disease EXCEPT:

Bringing together two copies of one of the common variants

What is the term describing the relative orientation of the two strands in a DNA helix, when the polarity of one strand is oriented in the opposite direction to that of the other strand?

Antiparallel

What happens to the two strands of a DNA molecule during replication?

Each strand is used as a template to create a complementary strand; each new strand pairs with an old strand; the two old strands separate.

Which of the following chromosomal events has led to this abnormal karyotype?

Translocation

What is the term for a DNA sequence that produces a functional RNA—structural, catalytic, or regulatory—or encodes a protein (or a set of closely related protein isoforms)?

Gene

Using these numbers, how many protein-coding genes would you estimate for the haploid human genome?

About 27,000

The DNA of human mitotic chromosomes is highly condensed; the DNA of human interphase chromosomes is fully extended.

False

Do these results suggest that the Martian organism has nucleosome-like structures in its chromatin? If so, what can you deduce about their spacing along the DNA?

Yes, and the nucleosomes are irregularly spaced along the DNA molecule.

Given the dynamic structure of the nucleosome, which one of the following effects is most important for determining the exact positions of nucleosomes along a stretch of DNA at any time in the cell?

The presence and nature of proteins bound to the DNA

Which one of the following proteins is called the linker histone?

Histone H1

Which one of the following forms of chromatin is the most common in a mammalian cell?

Quiescent euchromatin

Does trypsin treatment of nucleosome monomers appear to render a random population or a specific population of nucleosomes sensitive to micrococcal nuclease? How can you tell?

A specific population, because digestion of trypsin-treated nucleosomes with micrococcal nuclease protected globin cDNA to the same extent as DNase I-treated red-cell nuclei.

Phosphorylation of serine and acetylation of lysine in histone tails would both be expected to alter the interaction of the histone tails with DNA. Would these histone modifications be expected to increase or decrease the interaction of the histone with DNA?

Phosphorylation of serine would decrease DNA interactions; acetylation of lysine would decrease DNA interactions.

Which one of the following statements about histone variants is correct?

All histone variants have the characteristic histone fold.

Which of the following statements about histone marks on nucleosomes are correct?

I The combinations of modifications to histone tails constitute a well-defined histone code. II Because histone tails extend outward from nucleosomes, they are accessible except in condensed chromatin. III The marks on nucleosomes due to covalent changes to histones are dynamic, being constantly removed and added.

III

Based on these results, which of the tested proteins binds to the unmodified tails of histones H3 and H4?

Suv39h1 and Pc1

Which one of the following statements best explains the function of the E and I sites?

E and I are binding sites for factors that stimulate formation of heterochromatin.

Which one of the following descriptions applies to both the inheritance of heterochromatin and its spreading along the chromosome?

Both involve reader–writer complexes.

Which of the following modifications could explain the lack of p16 protein in these cancer cells?

I Formation of euchromatin at the p16 genes II Formation of heterochromatin at the p16 genes III Modification of histone tails at the p16 genes

II and III

Test your knowledge on genomic comparisons, evolutionary processes, and homologous genes with this quiz. Questions cover topics such as conserved and nonconserved regions, repeated sequences in the human genome, homologous genes, and the evolutionary process of eliminating individuals carrying mutations.

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