Porth's Pathophysiology, Tenth Edition - Chapter 4: Genetic Control of Cell Function and Inheritance
Following meiosis, which replicates germ cells and results in the formation of gametes, how many chromosomes do the gametes possess?
Correct response: 23 single chromosomes Explanation: Meiosis is limited to replicating germ cells and results in the formation of gametes or reproductive cells (ovum and sperm), each of which has only a single set of 23 chromosomes.
Individual differences in appearance, behavior, and disease susceptibility are a result of which of these?
Correct response: A haplotype Explanation: Small variations in gene sequence (termed a haplotype) are thought to be responsible for individual variations in appearance, behavior, and disease susceptibility. Mutations and consequent DNA repair are not believed to be responsible for the majority of these differences. Karyotyping refers to the process of chromosomal examination.
The gene responsible for a particular congenital cardiac anomaly is said to have complete penetrance. What are the clinical implications of this fact?
Correct response: All the individuals who possess the gene will exhibit the anomaly. Explanation: Penetrance represents the ability of a gene to express its function with complete (100%) penetrance, ensuring that all individuals possessing the gene will experience the phenotype in question. The disorder is not necessarily the result of multiple alleles or polygenetic inheritance. Complete penetrance does not mean that the disorder is a single-gene trait.
A pregnant woman carrying both a dominant (brown) and a recessive (blue) gene has a husband who has a recessive gene that pairs with her recessive gene. The woman asks what color eyes their baby will have. The best response would be:
Correct response: Blue Explanation: When two recessive genes combine for the lighter color eyes, the child would have the lighter (blue) eyes. Despite the woman having a recessive and dominant gene, it would not alter the color of the baby's eyes to a different shade.
A pregnant woman carrying both a dominant (brown) and a recessive (blue) gene has a husband who has a recessive gene that pairs with her recessive gene. The woman asks what color eyes their baby will have. The best response would be:
Correct response: Blue Explanation: When two recessive genes combine for the lighter color eyes, the child would have the lighter (blue) eyes. Despite the woman having a recessive and dominant gene, it would not alter the color of the baby's eyes to a different shade.
Which statement is not true concerning chromosomes?
Correct response: Chromosomes do not retain integrity between cell divisions. Explanation: Chromosomes retain integrity between cell divisions. All of the other statements are true.
There are two main approaches used in gene therapy: transferred genes can replace defective genes, or they can selectively inhibit deleterious genes. What are the compounds usually used in gene therapy?
Correct response: Cloned DNA sequences Explanation: Cloned DNA sequences are usually the compounds used in gene therapy. Messenger RNA carries the instructions for protein synthesis. Sterically stable liposomes are stable liposomes with long circulation times. Sites in the DNA sequence where individuals differ at a single DNA base are called single nucleotide polymorphisms (SNPs, pronounced "snips").
A physiology instructor asks the students about the purpose of the promoter region on a DNA strand. Which student response is most accurate?
Correct response: Contains amino acids that the RNA polymerase recognized and binds to, thus starting the replication process Explanation: During transcription, RNA polymerase recognizes the start sequence of a gene and attaches to the DNA. It is initiated by the assembly of a transcription complex composed of RNA polymerase and other associated factors. This complex binds to the double-stranded DNA at a specific site called the promoter region. Within the promoter region is the so-called "TATA box," which contains the crucial thymine-adenine-thymine-adenine sequence that RNA polymerase recognizes and binds to, starting the replication process. Exons are RNA sequences retained on the original RNA during splicing. tRNA delivers activated amino acids to proteins in the ribosome. When several triplet codons encode the same amino acid, the genetic code is said to be redundant.
When an infant is born with gene mutations in his/her cells, the errors may be a result of all of the following except _____________ of base pairs.
Correct response: Differentiation Explanation: Genetic mutations occur in germ cells (inherited errors) or somatic cells. Germ cell mutations can be spontaneous or an error of base pair deletion, substitution of one pair for a different pair, or rearrangement of the sequence of base pairs. Gene mutations represent accidental errors in duplication, rearrangement, or deletion of parts of the genetic code. Somatic cell mutations affect a cell line that differentiates into tissue types.
Which feature of a DNA molecule allows for precise replication?
Correct response: Double-stranded structure Explanation: The double-stranded structure of DNA molecules allows them to replicate precisely by separation of the two strands, followed by synthesis of two new complementary strands. Similarly, the base complementary pairing allows for efficient and correct repair of damaged DNA molecules. A precise complementary pairing of purine and pyrimidine bases allows for each nucleotide in a pair to bind with the bases on opposite DNA strands by hydrogen bonds that are extremely stable under normal conditions. The spiral staircase of paired bases allows for precise pairing of the bases. Several hundred to almost one million base pairs can represent a gene, the size being proportional to the protein product it encodes.
A researcher is involved in the investigation of an individual's genetic abnormality. Which situation could the researcher most likely rule out as the genetic cause of a mutation?
Correct response: Formation of an adenine-uracil base pair Explanation: RNA contains uracil instead of thymine. Formation of an adenine-uracil base pair is a normal event during assembly of messenger RNA. Substitution for cysteine or adenine produces possibilities for mutations.
The process of spermatogenesis results in which of the following?
Correct response: Four spermatids Explanation: The process of spermatogenesis results in four daughter cells called spermatids. Polar bodies are the result of oogenesis. A karyotype is the completed pictorial representation of chromosomes.
A nurse conducting a community education class on genetics tells the class that meiosis occurs in which type of cell?
Correct response: Gamete producing Explanation: The nurse should say that meiosis occurs in gamete-producing cells. Spermatids are daughter cells formed by meiosis. Polar body cells are formed through the process of oogenesis. Daughter cells are the result of both meiosis and mitosis.
Which method of genetic mapping focuses on the measurement of enzyme activity?
Correct response: Gene dosage studies Explanation: Gene mapping that is performed using dosage studies involves measuring enzyme activity. Hybridization studies and linkage studies do not perform genetic mapping by way of enzyme measurement, and haplotype mapping is a distinct type of genetic mapping.
A nurse recognizes that no two clients have the same susceptibility to disease and that this is partly due to:
Correct response: Haplotype Explanation: The nurse knows that each client's haplotype helps to account for individual client differences in disease susceptibility.
When discussing linkage studies, the instructor mentions that color blindness is found in a small section of the X chromosome and has been linked to development of which disease? Select all that apply.
Correct response: Hemophilia A Glucose-6-phosphate dehydrogenase (G6PD) deficiency Explanation: When two inherited traits occur together at a rate greater than would occur by chance alone, they are said to be linked. Color blindness has been linked to classic hemophilia A (i.e., lack of factor VIII) in some pedigrees; hemophilia A has been linked to glucose-6-phosphate dehydrogenase deficiency in others; and color blindness has been linked to glucose-6-phosphate dehydrogenase deficiency in still others. Because the gene for color blindness is found on the X chromosome, all three genes must be found in a small section of the X chromosome. Alzheimer disease and Down syndrome have not been associated with a linkage disorder.
A nurse is counseling a client on how recessive disorders are transmitted from parent to child. The nurse knows that recessive disorders occur when which allele is present?
Correct response: Homozygous recessive Explanation: Recessive disorders occur when the client has homozygous (two copies) of the recessive allele present.
Which of the following is the purpose of messenger RNA (mRNA)?
Correct response: It is necessary for protein synthesis. Explanation: mRNA provides the information needed for placing amino acids in their proper order for each specific type of protein.
Which term accurately describes the position of a gene on a chromosome?
Correct response: Locus Explanation: The position of a gene on a chromosome is called its locus. Alternate forms of a gene at the same locus are called alleles.
What ribonucleic acid (RNA) structure controls protein synthesis?
Correct response: Messenger RNA Explanation: After messenger RNA has been transcribed, it detaches from DNA and is processed by cutting, removing introns, and splicing the exon RNA sequences to produce a variety of mRNA molecules from a single gene. Once messenger RNA has been processed, it diffuses through the nuclear pores into the cytoplasm, where it controls protein synthesis. Transfer RNA reads the instructions and delivers the appropriate amino acids to the ribosome, where ribosomal RNA translates the instructions and provides the machinery needed for protein synthesis.
Which statement is true of genetic mutations?
Correct response: Mutations may result from environmental agents. Explanation: In addition to random errors, extrinsic factors such as environmental agents, chemicals, and radiation can induce errors in DNA duplication. DNA repair mechanisms resolve the majority of mutations. As a result, most mutations are corrected and do not result in pathology or death. Only those DNA changes that occur in germ cells can be inherited.
Crossing-over of chromatid segments during meiosis division 1 results in:
Correct response: New gene combinations Explanation: Crossing-over of chromatid segments allows for new gene combinations and increased genetic variability. It is unrelated to mutations. DNA synthesis occurs only during or after meiosis division 2. Because X and Y chromosomes are not homologs, they do not pair up to form bivalents during meiosis division 1.
A client states, "Both of my parents were overweight, but I've never really had any problems maintaining a healthy weight." How should the nurse best interpret the role of genetics in the client's observation?
Correct response: Obesity is a polygenic trait and does not result from a single gene at one locus. Explanation: Obesity is an example of a trait that has a genetic component but which is polygenic; it does not exist by virtue of one single genotype. As such, it is not considered to be a recessive or dominant trait. Because it is polygenic, the odds of having a child who is obese cannot be precisely determined.
Which conceptual model would be most helpful for a nurse to develop to show a client's family history of an inherited trait?
Correct response: Pedigree Explanation: A pedigree is a graphic method for portraying a family history of an inherited trait constructed from a carefully obtained family history. The Punnett square shows all the possible combinations for transmission of a single-gene trait. Phenotype is the complete physical, biochemical, and physiologic makeup of an individual.
What is the term that refers to the recognizable traits associated with specific genetic information stored in an individual base sequence?
Correct response: Phenotype Explanation: The phenotype refers to the recognizable traits, physical or biochemical, associated with a specific genotype. The genotype of a person is the genetic information stored in the base sequence triplet code. The position of a gene on a chromosome is called its locus, and alternate forms of a gene at the same locus are called alleles.
A nurse is completing a genetic map of a client's family. The client has brown eyes and his wife has blue eyes. Both the son and the daughter have brown eyes. Which of the following is the same in both children?
Correct response: Phenotype Explanation: Both the son and the daughter have the same phenotype, which is defined as the recognizable traits associated with a specific genotype.
The nurse knows that during the transcription process, which of these is true of RNA?
Correct response: Polymerase attaches to DNA. Explanation: During transcription, RNA polymerase recognizes the start sequence of a gene and attaches to the DNA. Exons are RNA sequences retained on the original RNA during splicing. tRNA delivers activated amino acids to proteins in the ribosome. When several triplet codons encode the same amino acid, the genetic code is said to be redundant.
Triplet codes of three bases are the genetic codes used in transmitting genetic information necessary for which one of these?
Correct response: Protein synthesis Explanation: Codons, triplet codes of bases, form the genetic code necessary for protein synthesis. Chromatin is a complex composed of DNA, RNA, and several types of protein. Polymerase enzymes synthesize RNA in the nucleus. DNA is composed of nucleotides, which are DNA strands bound together by hydrogen bonds.
Select the option that best describes the nitrogenous group that has two nitrogen rings and includes adenine and guanine.
Correct response: Purine base Explanation: The purine bases, adenine and guanine, have two nitrogen rings. Thymine and cytosine are pyrimidine bases.
A client with hepatitis C is scheduled to begin a new therapy that would block the progression of the virus by interfering with its genetic replication. What type of therapy is this client beginning?
Correct response: RNA interference Explanation: RNAi will stop genes from making unwanted disease proteins by interfering with gene expression. Gene transfer and replacement are protocols that aim to fix the problem gene, not the gene product. DNAi will silence a gene, not its product.
Select the statement that best describes the difference between ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
Correct response: RNA is a single-stranded molecule. Explanation: RNA is a single-stranded molecule, while DNA is a double-stranded molecule. The sugar in each nucleotide of RNA is ribose instead of deoxyribose. The pyrimidine base thymine in DNA is replaced by uracil in RNA. RNA, like DNA, is a large molecule made up of a long string of nucleotides.
Which process is considered one of the primary approaches to gene therapy?
Correct response: Replace defected genes Silence deleterious genes Explanation: Two main approaches are used in gene therapy: transferred genes can replace defective genes, or they can selectively inhibit deleterious genes. Cloned DNA sequences are usually the compounds used in gene therapy.
A researcher is involved in the production of insulin through recombinant DNA technology. Which statement about recombinant DNA is most accurate?
Correct response: The gene fragment responsible for insulin production can be isolated and reproduced. Explanation: The gene fragment that initiates and controls the production of several human proteins, including insulin, can be identified, separated, and reproduced by recombinant technology. Bacteria are used as a medium of reproduction, but they are not inherently capable of insulin production. Recombinant technology does not take place at the macrochromosomal level or at the microbase pair level.
Prenatal genetic testing that counts the number of Barr bodies in a chromosome is able to determine:
Correct response: The genetic sex of a child Explanation: The genetic sex of a child can be determined by microscopic study of cell or tissue samples because the total number of X chromosomes (which determine sex) is equal to the number of Barr bodies plus one. Genetic testing can reveal the presence of inherited disorders such as fragile X syndrome and hemophilia, but the focus of such testing is not the Barr bodies. Similarly, overall fetal viability is not ascertained from identifying Barr bodies.
A nurse in a genetic clinic reads that a client's karyotype includes a broken "p." The nurse interprets this to mean which of the following?
Correct response: The short arm of the X chromosome is broken. Explanation: The "p" refers to the short arm of the X chromosome, thus the nurse's interpretation should be that the short arm of the X chromosome is broken.
Which of the following is the definition of cytogenetics?
Correct response: The study of the structure and numeric characteristics of the cells' chromosomes Explanation: The study of cytogenetics is the study of the structure and numeric characteristics of the cells' chromosomes. The other statements are not true.
Like DNA, RNA is a long string of nucleotides encased in a large molecule. However, there are three aspects of its structure that makes it different from DNA. What are these aspects?
Correct response: The sugar in each nucleotide of RNA is ribose. RNA is a single-stranded molecule. RNA's thymine base is replaced by uracil. Explanation: RNA is a single-stranded rather than a double-stranded molecule. Second, the sugar in each nucleotide of RNA is ribose instead of deoxyribose. Third, the pyrimidine base thymine in DNA is replaced by uracil in RNA. All cells are supposed to have 23 pairs of chromosomes.
Select the base used in transmitting genetic information needed for protein synthesis that replaces thymine in a ribonucleic acid (RNA) structure.
Correct response: Uracil Explanation: A sequence of three of these bases forms the fundamental triplet code for 1 of the 20 amino acids used in protein synthesis in humans. This triplet code is called a codon. The molecular link between the DNA code of genes and the amino acid sequence of proteins is ribonucleic acid (RNA), a macromolecule similar in structure to DNA, except that uracil (U) replaces thymine (T) as one of the four bases.
A nurse is reading a report that refers to a gene on band 2, region 2 of the short arm of the X chromosome. The nurse understands that the location of the gene would typically be documented as which of the following?
Correct response: Xp22 Explanation: Reference to a gene located on band 2, region 2 of the short arm of the X chromosome would typically be documented as Xp22. The X represents the X chromosome, the "p" refers to the short arm of the X. The first "2" represents the band and the second "2" represents the region of the short arm where the gene is located.
A male child asks the nurse what chromosomes he would receive from his father. The best response would be:
Correct response: Y Explanation: Males (XY) get an X chromosome from their mother, and a Y chromosome from their father. If the father transmits an X chromosome, then the fetus would develop into a female (XX).
Which enzymes assist in repairing deoxyribonucleic acid (DNA) defects by recognizing a defect, cleaving the abnormal chain, and removing the distorted regions?
Correct response: endonucleases Explanation: Several repair mechanisms exist, and each depends on specific enzymes called endonucleases that recognize local distortions of the DNA helix, cleave the abnormal chain, and remove the distorted regions. The other options are not enzymes involved in this process.
Splicing of mRNA during processing permits a cell to:
Correct response: form different proteins. Explanation: Splicing permits a cell to produce a variety of mRNA molecules from a single gene, thus reducing how much DNA must be contained in the genome. Stop codes signal the end of a protein molecule, and RNA strands are then processed. Processing involves addition of certain nucleic acids to the RNA; splicing involves removing segments of RNA.
The International HapMap Project was created with two goals. One is the development of methods for applying the technology of these projects to the diagnosis and treatment of disease. The other is to map the ______ of the many closely related single nucleotide polymorphisms (SNPs) in the human genome?
Correct response: haplotypes Explanation: The establishment of the International HapMap Project was to map the haplotypes of the many closely related single nucleotide polymorphisms (SNPs) in the human genome and the development of methods for applying the technology of these projects to the diagnosis and treatment of disease. Four bases—guanine, adenine, cytosine, and thymine (uracil is substituted for thymine in RNA)—make up the alphabet of the genetic code. A sequence of three of these bases forms the fundamental triplet code used in transmitting the genetic information needed for protein synthesis. This triplet code is called a codon. Alternate forms of a gene at the same locus are called alleles.
A pregnant female has been told she is a carrier for fragile X syndrome. She asks, "What does that mean?" The health care provider explains that she is heterozygous for fragile X recessive trait, but this will only be a problem if:
Correct response: her mate also is a carrier of the recessive fragile X trait. Explanation: Offspring in whom the two alleles of a given pair are the same are called homozygotes. For example, a plant may have two alleles for wrinkled peas. Heterozygotes have different alleles at a gene locus. All offspring with a dominant allele manifest that trait. In human genetics, a carrier is a person who is heterozygous for a recessive trait and does not manifest the trait. For example, the gene for the genetic disorder Fragile X is recessive. Therefore, only persons with a genotype having two alleles for fragile X have the disease. In most cases, neither parent manifests the disease; however, both must be carriers. A blood transfusion will not fix the problem.
Identifying the genetic sex of a child is based on finding intracellular Barr bodies that consist of:
Correct response: inactive chromatin material. Explanation: Barr bodies are present only when there is more than one X in each cell, signifying a female. The extra X is inactivated and stored as chromatin material that can be visualized in epithelial cells. Genetically normal males have one X and one Y chromosome, so a Barr body is not present. Male-specific encoding is on the Y chromosome only. The maternal and paternal chromosomes of a pair are called homologous chromosomes (homologues).
When discussing upcoming chromosome studies, a client asks, "What kind of sample are they going to take to do these tests?" The nurse replies, "The most common cells used for this purpose are:
Correct response: lymphocytes from a venous blood specimen." Explanation: Chromosome studies can be done on any tissue or cell that grows and divides in culture. Lymphocytes from venous blood are frequently used for this purpose.
An individual's muscle cell is undergoing the process of protein synthesis. During the process of translation, what event will take place?
Correct response: mRNA will transfer genetic instructions to rRNA. Explanation: During the translation phase of protein synthesis, the instructions transcribed from DNA to mRNA are transferred to the rRNA of ribosomes located in the cytoplasm. Each of the other listed processes takes place during the transcription phase.
A nurse administering a synthetic insulin to a client knows that production of synthetic insulin was made possible by:
Correct response: recombinant DNA technology. Explanation: The nurse knows that the production of synthetic insulin was made possible through recombinant DNA technology.
Most human traits are determined by multiple pairs of genes, many with alternate codes, accounting for some dissimilar forms that occur with certain genetic disorders. What type of inheritance involves multiple genes at different loci, with each gene exerting a small additive effect in determining a trait?
Correct response: Polygenic inheritance Explanation: Polygenic inheritance involves multiple genes at different loci, with each gene exerting a small additive effect in determining a trait. Multifactorial inheritance is similar to polygenic inheritance in that multiple alleles at different loci affect the outcome; the difference is that multifactorial inheritance includes environmental effects on the genes. Monofactorial inheritance is nonexistent as is collaborative inheritance.
DNA fingerprinting is based in part on recombinant DNA technology and in part on those techniques originally used in medical genetics to detect slight variations in the genomes of different individuals. These techniques are used in forensic pathology to compare specimens from the suspect with those of the forensic specimen. What is being compared when DNA fingerprinting is used in forensic pathology?
Correct response: The banding pattern Explanation: Banding patterns are analyzed to see if they match. Four bases—guanine, adenine, cytosine, and thymine (uracil is substituted for thymine in RNA)—make up the alphabet of the genetic code. A sequence of three of these bases forms the fundamental triplet code used in transmitting the genetic information needed for protein synthesis. The small variation in gene sequence (termed a haplotype) is thought to account for the individual differences in physical traits, behaviors, and disease susceptibility. Chromosomes contain all the genetic content of the genome.
