GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Genome Evolution
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #1 : Help With Genome Evolution
Why are rRNA genes more useful in molecular typing than other genes?
rRNA genes are only in bacteria and archaea
Ribosomal RNA (rRNA) genes have both highly conserved and variable regions
rRNA genes are only in eukaryotes
There are multiple rRNA genes in each organism
None of these
Ribosomal RNA (rRNA) genes have both highly conserved and variable regions
The correct answer is that rRNA genes have both highly conserved and highly variable regions. Molecular typing is the process of identifying species from a microbiome by analysis of common molecules or genes. All organisms including eukaryotes, prokaryotes, and archaea, (but not viruses) have multiple rRNA genes. Given that rRNA genes have highly conserved regions, it allows researchers to identify transcripts/genes as rRNA genes in unknown species. Comparing the sequences of the variable regions of the rRNA genes allows researchers to identify the species of the organism from which it is derived.
Example Question #2 : Help With Genome Evolution
What is orthology in the context of genome comparisons?
None of these
A homologous DNA sequence that was derived from the same ancestral sequence
A gene that has the same DNA sequence as that in another species
A gene that has the same function as another gene sequence
A homologous DNA sequence that was derived from a gene duplication event
A homologous DNA sequence that was derived from the same ancestral sequence
An orthologous gene is one that is descended from a common ancestral sequence. So, when two sequences from different species are compared, they are orthologs if they have the same evolutionary history. A paralogous gene is the case in which a similar gene sequence is derived from a genome duplication event, and do not have a evolutionary relationship. These genes often develop different functions, unlike orthologs.
Example Question #3 : Help With Genome Evolution
What is the physiological purpose of a tandem gene array?
Encoding of huge numbers of important genes simultaneously
Tandem arrays are just an artifact of DNA duplication and replication processes
Tandem arrays are a species specific genome feature used in species specific ways
Many copies of a genes serve to make it less likely that there are mutated copies
None of these
Encoding of huge numbers of important genes simultaneously
Tandem arrays are used for extremely important genes, like ribosomal RNA genes that are vital for organism function. The arrays serve to allow massive parallelized encoding of these genes, because many copies are required.
Example Question #4 : Help With Genome Evolution
Why are rRNA genes and internal transcribed spacers (ITS) frequently used for organismal identification and evolutionary comparisons between organisms?
Only bacteria have ITS and only eukaryotes have rRNA genes
rRNA genes and ITS have highly conserved regions and highly divergent regions
rRNA genes and ITS are highly conserved among all species
None of the other answers
rRNA genes and ITS are highly divergent among all species
rRNA genes and ITS have highly conserved regions and highly divergent regions
The correct answer is rRNA genes and ITS have highly conserved regions and highly divergent regions. Both prokaryotes and eukaryotes have rRNA genes and ITS, making these ideal targets for molecular typing. In order to amplify, then sequence these regions for evolutionary comparisons, universal primers are designed to anneal within the highly conserved regions and amplify through the highly divergent regions. The divergent regions of rRNA genes and ITS allow for specie to specie comparison and identification.
Example Question #5 : Help With Genome Evolution
Genome projects on Drosophila and Anopheles have identified approximately 6,000 1:1 orthologs ranging from 100% to 20% identity. Why were no orthologs at a lower identity identified?
It is almost impossible to align these sequences
There are many orthologs present at other ratios clouding the data
No orthologs would exist below this threshold
None of these are correct
These insects are too closely related to identify them
It is almost impossible to align these sequences
When two sequences have less than 20% identity, it is almost impossible to align them and identify that they are actually orthologs. This is especially the case in huge genome data sets, in which it is impossible to find matching sequences by hand.
Example Question #6 : Help With Genome Evolution
What are pseudogenes?
None of these are correct
A gene that has multiple copies in the genome
A gene with a similar function to another gene
A gene resulting from a duplication event that has degenerated and lost its function
A gene that is no longer functional
A gene resulting from a duplication event that has degenerated and lost its function
The key factors that distinguish pseudogenes are that they are sequences that result from a duplication event in the genome, but have since mutated without selection pressure and have become nonfunctional.
Example Question #7 : Help With Genome Evolution
Organisms with extremely large genomes tend to have high amounts of what?
None of these are correct
Intron duplication
Viral DNA insertions
Transposons
Recombination
Transposons
Organisms with large genomes tend to have very high levels of transposons. For instance, this is the case in our own genomes. It is hypothesized that in some organisms, there is a breakdown of systems that control insertion of transposons into the genome, resulting in large expansions.
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