Question 1

If mutagenizing a number of Drosophila results in several observable phenotypes but also in several lethal mutations,does this mean that recessive lethal mutations cannot be studied further?

Accepted Answer

Even though the lethal mutations result in death, it is possible to recover the lethal allele from heterozygous siblings who carry one copy of the mutation but do not show the lethal phenotype. This can allow for further study of the recessive lethal mutation.

Question 2

If a mutagenesis screen provides some number (e.g.,24)of alleles shown by complementation analysis to be in the same gene,which of the following is true?

Accepted Answer

These mutants can be used to identify the role of the gene in metabolism because they represent different alleles of the same gene, which can help elucidate its function.

Question 3

In 1978,Arber,Smith,and Nathans won the Nobel Prize in Physiology and Medicine for work with restriction enzymes.Which of the following can still be performed without using these enzymes?

Accepted Answer

While restriction enzymes have greatly aided in genetic research and technology, genetic mapping can still be performed without using these enzymes.

Question 4

Whether libraries are cDNA or genomic,whether amplification is based on PCR or cloning,and whether screening is done with northern or Southern blotting or probes,all are based on which of the following?

Accepted Answer

All of the techniques mentioned rely on the principle of complementary base pairing between nucleic acid sequences in order to identify, amplify, or isolate specific genetic information. This includes complementary binding between probes and target sequences in Northern or Southern blotting, annealing of primers in PCR amplification, and hybridization of cDNA or genomic sequences in library construction. Complementation, reverse transcription, and reverse translation are not directly related to these techniques. Gene expression may be involved, but is not the underlying principle that all of these techniques are based on.

Question 5

-Because of redundancy in the genetic code,some amino acids can have more than one possible codon.Use the table above and select which of the answer choices is a possibility for the following amino acid sequence: valine,glycine,glycine,cysteine,tyrosine

Accepted Answer

Valine (Val) can be coded by GUA, Glycine (Gly) by GGG or GGC, Cysteine (Cys) by UGU, and Tyrosine (Tyr) by UAC. Option D matches these codons.

Question 6

-In a disease associated with a nucleotide repeat,anticipation is often noticed in subsequent generations,usually associated with a more severe phenotype.Which of the following is a more likely cause of anticipation?

Accepted Answer

There is more frequent unequal crossing over.

Question 7

In the construction of a YAC library,each chromosome has the advantage of being able to hold very long DNA sequences.However,besides selectable marker(s)the YAC vector must minimally include which of the following?

Accepted Answer

The YAC vector must minimally include a centromere, telomeres, and yeast origin in order to properly replicate and segregate in yeast cells. These elements ensure that the YAC will be maintained as a stable extrachromosomal entity in the yeast cell, allowing for the insertion and propagation of long DNA sequences. The inclusion of a bacterial origin (ori) or cos site(s) and origin are also commonly used in YAC vectors, but are not strictly necessary for YAC construction. Therefore, choices A and B are not the best choices. While D and E both contain a centromere, only C includes all three necessary elements for YAC vector construction.

Question 8

A researcher wants to mutagenize an organism.He is not in need of a large number of mutants but is more concerned with being able to find and then to amplify the mutated sequence.Which of the following would therefore be more useful?

Accepted Answer

The answer of A researcher wants to mutagenize an organism.He...

Question 9

Before Muller's discovery that radiation induces mutation,scientists had to work on mutations that were found solely by phenotype differences in natural populations.Which of the features of Drosophila made it a fortuitous choice for Morgan and his colleagues?

Accepted Answer

Drosophila has a large number of easily visible phenotypes, which made it easier for Morgan and his colleagues to identify mutations and study their inheritance patterns. Its short generation time and ability to produce large numbers of offspring also made it a convenient organism for genetics research.

Question 10

You have a DNA sequence of 1600 bp.To characterize it,you decide to make a restriction map.Cutting with the first enzyme,you show by electrophoresis that the fragments produced are 400 and 1200 bp respectively.After using the second enzyme,you recover 700-bp and 900-bp fragments.After treatment with both enzymes,fragments were 300,400,and 900 bp.Which is the correct map?

Accepted Answer

The answer of You have a DNA sequence of 1600...

Question 11

-Which of the following would make a human disorder-causing allele or gene easiest to locate?

Accepted Answer

A single patient with a chromosomal translocation associated with the gene would provide a clear starting point for mapping the location of the gene. By identifying the breakpoints of the translocation, researchers can determine which genes are physically interrupted or relocated, providing strong clues about the location and identity of the disease-causing gene.

Question 12

Some restriction enzymes cut at specific and unambiguous sequences (e.g.,NotI at GCGGCCGC).As such,the distance between two such sites in a large random DNA sequence is 4⁸.However,the sequence recognized by XhoII is said to be ambiguous (Pu-GATC-Py,where Pu = any purine and Py any pyrimidine).What,therefore,is the expected distance between two XhoII sites in a large random sequence?

Accepted Answer

The sequence recognized by XhoII is Pu-GATC-Py, which means there are 2 possibilities for the first and last positions (purine or pyrimidine), and 4 possibilities for each of the four bases in GATC. Therefore, the expected distance is 2 × 4 × 4 × 4 × 4 × 2.

Question 13

In producing a recombinant plasmid to be used to clone a given donor insert,it is possible to cut both the donor and plasmid with the same restriction enzyme,resulting in complementary sticky ends.Assuming plenty of plasmid DNA is available,why is further selection necessary before the introduction of the plasmid into a cellular system?

Accepted Answer

Even with complementary sticky ends, there is a possibility that the donor insert could be inserted into the plasmid in the incorrect orientation. Therefore, selection is necessary to ensure that only plasmids with the correctly oriented donor insert are introduced into the cellular system. Choices A, B, C, and D are not relevant to the need for further selection with complementary sticky ends.

Question 14

One use of PCR has been to monitor the trafficking of endangered organisms.Suppose that one suspect was accused of illegally importing a specific animal,but the suspect asserts that the young animal had been bred in this country from two resident zoo animals.How would you best proceed?

Accepted Answer

Using DNA from hair follicles of the supposed zoo parents and of the supposed offspring to compare sequences amplified with primers for a highly polymorphic region would be the best option. This method can determine the relatedness of the suspected animal and the supposed parents by comparing the sequences of highly polymorphic regions. If there is a match, it supports the suspect's assertion that the young animal was bred in the country.

Question 15

Current sequencing technologies have major advantages over the dideoxy method because they produce more sequence in less time and at less cost.Which of the following would provide further advantage?

Accepted Answer

The answer of Current sequencing technologies have major advantages over...

Question 16

Among the attributes of model organisms,which of the following characteristics of C.elegans makes it useful for mutagenesis?

Accepted Answer

The answer of Among the attributes of model organisms,which of...

Question 17

Which of the following vectors would be most efficient to use to amplify fragments ~300 kb in length?

Accepted Answer

YACs (yeast artificial chromosomes) are designed to accommodate large fragments of DNA (up to 1 Mb) and have been used successfully to clone fragments of up to 300 kb in length. BACs (bacterial artificial chromosomes) can also accommodate larger fragments, but YACs have a higher transformation efficiency in yeast and can be maintained as circular molecules, making them more stable than BACs. Plasmids, lambda phage, and cosmids are not suited for cloning fragments of this length.

Question 18

In selecting recombinant bacteria,cells are chosen that are resistant to a specific antibiotic.How are the bacteria made resistant?

Accepted Answer

The antibiotic resistance is encoded in the vector, which allows for the selection of bacteria that have successfully taken up the vector containing the recombinant DNA.

Question 19

Genes for regulatory elements,such as creb,were found to be important in animal learning.Which of the following would increase the probability that such an element is studied throughout the animal kingdom?

Accepted Answer

The finding that creb is highly conserved increases the likelihood that it is studied throughout the animal kingdom because it suggests that the gene serves an important function across a wide range of species. Conserved genes are those that have remained relatively unchanged (in terms of DNA sequence) across evolution, indicating that they are important for survival and/or reproduction. Therefore, creb's high conservation suggests that it plays a critical role in animal learning and behavior, making it a prime candidate for study in diverse animal models.

Question 20

In forensics,the laws in the United States and elsewhere allow the establishment of databases of PCR amplification of short tandem repeats (STRs)of the Y chromosome.Which of these statements would provide an appropriate basis for making such databases divided by ethnicity?

Accepted Answer

Different heritage groups have different levels of Y chromosome polymorphisms, which can be useful in establishing databases for forensic investigations. This can aid in identifying suspects by narrowing down the pool of potential matches based on ethnic background. However, it is important to note that ethnicity alone should not be the sole factor in suspect identification, as it can lead to racial profiling and other forms of discrimination.

Quiz 16: Forward Genetics and Recombinant DNA Technology