Question 1

Which statement best describes the mechanism of action of miRNAs in blocking expression of proteins?

Accepted Answer

Single-stranded miRNA, in association with the RISC complex, binds to the complementary sequence in the 3ʹ UTR of mRNAs. This interaction blocks translation and induces degradation of the mRNA, effectively silencing the gene.

Question 2

Which of the following transposable elements accounts for ~21% of the human genome?

Accepted Answer

Long interspersed elements (LINEs) account for approximately 21% of the human genome. Short interspersed elements (SINEs) account for around 13%, retrovirus-like elements account for less than 1%, and DNA transposons account for less than 3%.

Question 3

Which statement about LINEs is false?

Accepted Answer

Mutations induced by LINEs are not exclusively harmful. Some mutations may be neutral or even beneficial. However, because of their ability to cause genetic instability, LINEs are more likely to cause harmful mutations than other types of DNA sequences.

Question 4

In dogs, the Fgf4 gene encodes a protein that regulates bone growth, and in its normal chromosomal location, Fgf4 yields dogs with long legs. Which statement best explains the mechanism leading to a short-legged phenotype in dogs?

Accepted Answer

The short-legged phenotype in dogs is due to the retrotransposition of the Fgf4 gene into a location where it is abnormally expressed, as described in option C. This abnormal expression disrupts the normal regulation of bone growth, leading to shorter legs.

Question 5

A pseudogene is a

Accepted Answer

A pseudogene is a gene that arose through gene duplication but after acquiring mutations became nonfunctional. It is a remnant of a functional gene that has become inactive in the course of evolution.

Question 6

Partial digestion of chromatin with micrococcal nuclease was found to yield DNA fragments approximately 200 base pairs long. What accounts for this phenomenon?

Accepted Answer

The binding of proteins to DNA in chromatin may protect regions of DNA from nuclease digestion, resulting in the observed fragments being approximately 200 base pairs long.

Question 7

Extensive digestion of chromatin with micrococcal nuclease was found to yield particles called nucleosome core particles that appear as beads when viewed by electron microscopy. Which of the following is not found in the nucleosome core particle?

Accepted Answer

The nucleosome core particle contains two molecules each of H2A, H2B, H3, and H4 proteins, but only one molecule of the linker histone, H1, is found outside of the core particle. Therefore, the correct answer is D, as it is the only option that is not found within the nucleosome core particle.

Question 8

A centromere is a region of the chromosome that

Accepted Answer

A centromere plays a critical role in ensuring the correct distribution of duplicated chromosomes to daughter cells during mitosis. It is the site of kinetochore assembly, which allows the attachment of spindle fibers during cell division, ensuring proper segregation of chromosomes. The other answer choices do not accurately describe the role of the centromere.

Question 9

Which statement describes centromeric sequences in humans?

Accepted Answer

Centromeric sequences in humans are characterized by long stretches of repetitive DNA, including alpha satellite DNA, which spans 1-5 million base pairs. This structure is crucial for chromosome segregation during cell division.

Question 10

In the chromatin around centromeres, nucleosomes are present that have a unique structure in which the core protein _______ is replaced by _______, and this variant of the nucleosome is required for protein assembly at the kinetochore.

Accepted Answer

The unique nucleosomes in the chromatin around centromeres contain a variant of the core protein histone H3, called CENP-A. This variant is required for protein assembly at the kinetochore. Histone H5 is not a known variant and histone H1 is a linker histone, not a core histone, and is not typically found in nucleosomes around centromeres.

Question 11

The function of telomeres is to

Accepted Answer

Telomeres help protect the ends of linear chromosomes from degradation and fusion with neighboring chromosomes, and also ensure successful replication and maintenance of the chromosome during cell division.

Question 12

Suppose you are working on a set of experiments using Western blotting. Using an antibody that recognizes amino sequences encoded by exon 3 of a five-exon gene, you have demonstrated that a protein is highly expressed in a particular cell line. To assess the mRNA, you design reverse transcriptase polymerase chain reaction (rtPCR) primers to exons 2 and 4, which flank exon 3. Despite all your efforts, you cannot amplify an mRNA. You know that it is indeed expressed, since the protein is detectable. You also know that your controls are working and your experimental procedure is sound, because you are able to detect an mRNA for the other cell lines. Given what you know about the "central dogma" and gene structure, how might you explain this inability to identify the mRNA encoding this exon 3 protein?

Accepted Answer

The answer of Suppose you are working on a set...

Question 13

Briefly describe two molecular mechanisms that give rise to gene duplication.

Accepted Answer

The answer of Briefly describe two molecular mechanisms that give...

Question 14

Processed pseudogenes do not have introns. Why not?

Accepted Answer

The answer of Processed pseudogenes do not have introns. Why...

Question 15

Arabidopsis, and many other plants, have more protein coding genes than humans. What molecular mechanism is likely responsible for an organism so much less complex than humans having so many protein-coding genes?

Accepted Answer

The answer of Arabidopsis, and many other plants, have more...

Question 16

A "complete" sequence of the Drosophila genome has recently been obtained; that is, the part of the genome that lies within euchromatin (and only that part) has been sequenced. Why would sequencing be focused on euchromatin, and why is the acquisition of the Drosophila genome sequence now considered to be virtually complete?

Accepted Answer

The answer of A "complete" sequence of the Drosophila genome...

Question 17

Which genes are actively undergoing transcription during mitosis?

Accepted Answer

The answer of Which genes are actively undergoing transcription during...

Question 18

What are two important functions of centromeres?

Accepted Answer

The answer of What are two important functions of centromeres?...

Question 19

Why is it thought that the DNA sequences of centromeres are not critical to their function, whereas the chromatin structure is?

Accepted Answer

The answer of Why is it thought that the DNA...

Question 20

Because telomeres are longer in the cells of infants than they are in older people, it has been hypothesized that telomere length determines a cell's life expectancy. Thus, some believe that finding a way to extend the length of telomeres in older people would extend their life expectancy. What is a possible problem with this approach?

Accepted Answer

The answer of Because telomeres are longer in the cells...

Quiz 6: Genes and Genomes