Genetics, DNA, and Molecular Biology
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GRE › Genetics, DNA, and Molecular Biology
Hemophilia A is a blood clotting disorder that is usually inherited as an X-linked recessive trait. If a woman who does not have hemophilia A has a daughter with a man who does not have hemophilia A, what is the probability that the daughter will have hemophilia A if the maternal grandfather did have hemophilia A?
Explanation
X-linked recessive inheritance dictates that expression of themutant phenotype will only occur if the individual is homozygous for the mutation on the X-chromosomes. Therefore, a female must have inherited two mutant X-chromosomes to have hemophilia A, while a male only requires one mutant X-chromosome to have the disorder. By virtue of the father not having hemophilia A, we know the daughter is inheriting at least one wild-type X-chromosome, and therefore there is zero chance she will be homozygous and have hemophilia A.
Hemophilia A is a blood clotting disorder that is usually inherited as an X-linked recessive trait. If a woman who does not have hemophilia A has a daughter with a man who does not have hemophilia A, what is the probability that the daughter will have hemophilia A if the maternal grandfather did have hemophilia A?
Explanation
X-linked recessive inheritance dictates that expression of themutant phenotype will only occur if the individual is homozygous for the mutation on the X-chromosomes. Therefore, a female must have inherited two mutant X-chromosomes to have hemophilia A, while a male only requires one mutant X-chromosome to have the disorder. By virtue of the father not having hemophilia A, we know the daughter is inheriting at least one wild-type X-chromosome, and therefore there is zero chance she will be homozygous and have hemophilia A.
Hemophilia A is a blood clotting disorder that is usually inherited as an X-linked recessive trait. If a woman who does not have hemophilia A has a daughter with a man who does not have hemophilia A, what is the probability that the daughter will have hemophilia A if the maternal grandfather did have hemophilia A?
Explanation
X-linked recessive inheritance dictates that expression of themutant phenotype will only occur if the individual is homozygous for the mutation on the X-chromosomes. Therefore, a female must have inherited two mutant X-chromosomes to have hemophilia A, while a male only requires one mutant X-chromosome to have the disorder. By virtue of the father not having hemophilia A, we know the daughter is inheriting at least one wild-type X-chromosome, and therefore there is zero chance she will be homozygous and have hemophilia A.
Which of the following is true about the effects of epigenetics on gene expression?
Modification of histone lysine residues alters gene expression by changing the affinity between DNA and histones
Modification of chromatin lysine residues alters gene expression by changing the affinity between DNA and chromatin
Modification of histone arginine residues alters gene expression by changing the affinity between DNA and histones
Modification of nucleosome lysine residues alters gene expression by changing the affinity between DNA and histones
None of the other answers
Explanation
Methylation and acetylation of histones occurs on lysine residues, thereby decreasing or increasing gene expression, respectively. Methylation increases the affinity for histones and DNA, where acetylation decreases the affinity for histones and DNA. Gene expression is in part controlled by modification of histone proteins, rather non-histone chromosomal proteins.
Which prokaryotic polymerase is primarily responsible for filling in DNA nucleotides into the gap created by the removal of RNA primers?
DNA polymerase I
DNA polymerase II
DNA polymerase III
RNA polymerase
Reverse transcriptase
Explanation
DNA polymerase I replaces the RNA primer gap with DNA nucleotides. This polymerase is unique in that it has 5' 
Which of the following best describes an oncogene?
A gene that causes uncontrollable growth
A gene that regulates cell growth
A gene that stimulates apoptosis in cells
A gene that no longer makes a viable protein
Explanation
Oncogenes can be thought of as cancerous genes, or rather a gene that has the potential to cause cancer. They typically occur when a normal proto-oncogene undergoes a mutation. Proto-oncogenes normally code for growth and development in cells, and tightly regulate these processes. If mutated, these newly cancerous genes can stimulate unregulated growth, a symptom characteristic of cancerous cells.
An error occurs during DNA replication, resulting in the insertion of a base pair. Replication of the original 3' DNA strand (template) produces a mutant 3' strand (mutant), as diagrammed below:
Template
3' - AUGGCCATTTTTATA - 5'
Mutant
3'- AUGCGCCATTTTTATA - 5'
Of the answers below, which best describes the type of mutation depicted above?
Frameshift mutation
Missense mutation
Nonsense mutation
Duplication mutation
Repeat expansion
Explanation
The addition of a number of nucleotides that is not a multiple of three shifts the reading frame of the codons in the gene. One base pair was inserted early in the strand, thus shifting the codon reading frame +1 to the right.
Missense and nonsense mutations imply base pair substitutions, which did not occur in the diagram. Similarly, nothing was duplicated, and repeat expansion would require multiple repetitions of a short DNA sequence.
Which of the following is true about the effects of epigenetics on gene expression?
Modification of histone lysine residues alters gene expression by changing the affinity between DNA and histones
Modification of chromatin lysine residues alters gene expression by changing the affinity between DNA and chromatin
Modification of histone arginine residues alters gene expression by changing the affinity between DNA and histones
Modification of nucleosome lysine residues alters gene expression by changing the affinity between DNA and histones
None of the other answers
Explanation
Methylation and acetylation of histones occurs on lysine residues, thereby decreasing or increasing gene expression, respectively. Methylation increases the affinity for histones and DNA, where acetylation decreases the affinity for histones and DNA. Gene expression is in part controlled by modification of histone proteins, rather non-histone chromosomal proteins.
An error occurs during DNA replication, resulting in the insertion of a base pair. Replication of the original 3' DNA strand (template) produces a mutant 3' strand (mutant), as diagrammed below:
Template
3' - AUGGCCATTTTTATA - 5'
Mutant
3'- AUGCGCCATTTTTATA - 5'
Of the answers below, which best describes the type of mutation depicted above?
Frameshift mutation
Missense mutation
Nonsense mutation
Duplication mutation
Repeat expansion
Explanation
The addition of a number of nucleotides that is not a multiple of three shifts the reading frame of the codons in the gene. One base pair was inserted early in the strand, thus shifting the codon reading frame +1 to the right.
Missense and nonsense mutations imply base pair substitutions, which did not occur in the diagram. Similarly, nothing was duplicated, and repeat expansion would require multiple repetitions of a short DNA sequence.
Which prokaryotic polymerase is primarily responsible for filling in DNA nucleotides into the gap created by the removal of RNA primers?
DNA polymerase I
DNA polymerase II
DNA polymerase III
RNA polymerase
Reverse transcriptase
Explanation
DNA polymerase I replaces the RNA primer gap with DNA nucleotides. This polymerase is unique in that it has 5'