PATHO

5. An accurate description of a silent mutation is: A a change in the DNA without a change in amino acid. B insertion or deletion of one or more base-pairs. C an increase in the number or frequency of mutations. D a mutation that occurs in the absence of exposure to a mutagen.

A A silent mutation occurs if a base-pair is changed but the DNA still codes for the same amino acid. This is possible as amino acids have more than one codon (triplet) that codes for them. Insertion or deletion of one or more base-pairs is a frameshift mutation and can change the entire reading frame. A mutagen is an agent that increases the frequency of mutations. A spontaneous mutation occurs when a mutation occurs but there is no exposure to a mutagen.

2. Which describe epigenetic mechanisms? A DNA methylation, histone modifications, RNA-based modifications. B RNA methylation, protease modifications, DNA-based modifications. C Genetic disruption, protease modifications, DNA-based modifications. D Histone modification, DNA-based modifications, RNA methylation.

A DNA methylation, histone modifications, RNA-based modifications are epigenetic mechanisms. RNA methylation and protease modifications are not. Additionally DNA-based modifications although important are not mechanisms of epigenetics.

1. Which statement best captures the definition of epigenetics? A The study of switching on or silencing genes. B The study of pharmacology and genes. C The study of inherited phenotype traits. D The study of DNA.

A Epigenetics is the study of mechanisms that will switch genes "on," such that they are expressed, and "off," such that they are silenced. Epigenetic mechanisms include chemical modifications to DNA and associated histones and the production of small RNA molecules. Gene regulation by epigenetic processes can occur at the level of either transcription or translation.

4. Which is correct with regard to facioscapulohumeral muscular dystrophy (FSHMD)? A Arises through loss of normal methylation. B Arises through gain of abnormal methylation. C Has limited effect on skeletal musculature. D Persons with FSHMD rarely live past 30 years.

A FSHMD is a disease whose phenotype arises through loss of normal methylation rather than gain of abnormal methylation. Symptoms of the disease include adverse impacts on skeletal musculature. Though life span is not typically reduced by the disease, wheelchair use becomes necessary late in life for a subset of individuals.

14. An autosomal dominant gene transmission results in: A the affected parent transmitting the gene to half of his or her children. B the affected gene being found in males only. C the skipping of generations for transmission. D females transmitting the gene more often than males.

A The affected parent will transmit the trait to half of the children (approximately). This is because in each match there is a 50% chance that either a normal gene or an affected gene will be transmitted to the child. The affected gene is found equally in males and females, both sexes transmit the trait equally, and there is no skipping of generations.

1. Which bases are single-ringed structures in the DNA molecule? A Cytosine and thymine B Cytosine and adenine C Thymine and guanine D Guanine and adenine

A The single-ringed bases (pyrimidines) are cytosine and thymine. The double-ringed bases (purines) are adenine and guanine.

10. Which term describes a cell that does not contain a multiple of 23 chromosomes? A Aneuploid B Monsomy C Trisomy D Tetraploidy

A The term aneuploid means that the cell does not contain a multiple of 23 chromosomes. Monsomy is the presence of only one copy of a given chromosome in a cell. Trisomy is when there are three copies of a chromosome. Tetraploidy is a cell that contains 92 chromosomes.

17. The DNA is composed of: (select all that apply) A phosphate. B deoxyribose. C pyrimidine base. D ribosome. E purine base.

A B C E Genes are composed of DNA, which has three basic components: the five-carbon monosaccharide deoxyribose; a phosphate molecule; and four types of nitrogenous bases. Two of the bases, cytosine and thymine, are single carbon-nitrogen rings called pyrimidines. The other two bases, adenine and guanine, are double carbon-nitrogen rings called purines. The four bases are commonly represented by their first letters: A, C, T, and G. A ribosome is an RNA complex that is synthesized in the nucleolus and secreted into the cytoplasm.

10. Which of the following characterizes Beckwith-Wiedemann syndrome? A Increased predisposition to cancer B Sometimes identifiable at birth C Typically small birth stature (lower 10 percentile) D Increased predisposition to developing Wilms' tumor. E Some experience asymmetrical overgrowth of a limb.

A B D E Beckwith-Wiedemann syndrome is usually identifiable at birth because of large size for gestational age, neonatal hypoglycemia, a large tongue, creases on the earlobe, and omphalocele (birth defect infant intestines). Children with Beckwith-Wiedemann syndrome have an increased risk of developing Wilms' tumor or hepatoblastoma. Usually children with Beckwith-Wiedemann syndrome are severely retarded. Some children with Beckwith-Wiedemann syndrome also develop asymmetrical overgrowth of a limb or one side of the face or trunk (hemihyperplasia).

9. Which is true about Angelman syndrome? (select all that apply) A Inherited from the mother B Characterized by mild mental retardation C Typically manifests in seizures D Associated with an ataxic gait

A C D A 4 Mb deletion, when inherited from the mother, causes Angelman syndrome which is characterized by severe mental retardation, seizures, and an ataxic gait.

8. Which is true of Prader-Willi syndrome? (select all that apply) A Associated with long arm deletion of chromosome 15 B Taller than average due to excessive eating C Severe mental retardation D Obesity due to overeating E Hypogonadism

A D E A well-known disease example of imprinting is associated with a deletion of about 4 million base (Mb) pairs of the long arm of chromosome 15. When this deletion is inherited from the father, the child manifests Prader-Willi syndrome whose features include short stature, hypotonia, small hands and feet, obesity, mild to moderate mental retardation, and hypogonadism.

6. How does the drug 5-azacytidine work? It: A inhibits histone deacetylase. B demethylates DNA. C recodes miRNA. D increases chromatin compaction.

B 5-Azacytidine has been used as a therapeutic drug in the treatment of leukemia and myelodysplastic syndrome. A cytosine analog, 5-azacytidine, is incorporated into DNA opposite its complementary nucleotide, guanine. The drug is a DNA demethylator. It does not work on histones and it does not recode miRNA. Chromatin compaction is a function of histone deacetylase Inhibitors.

7. Which is true about epigenetic modifications? They: A alter gene expression by modifying DNA. B can be influenced by diet and lifestyle. C occur only at the time of birth. D at best, only involve benign processes.

B Epigenetic modification alters gene expression without changes to DNA sequence. Environmental factors, such as diet and exposure to certain chemicals, may cause epigenetic modifications. These modifications can occur as adults and can result in devastating disease processes such as cancer.

9. Which is a characteristic of a somatic cell? A somatic cell: A contains three different cell types. B contains 46 chromosomes. C has gametes that are diploid cells. D contains diploid cells that are formed through meiosis.

B Somatic cells have 46 chromosomes in the nucleus and are considered diploid cells. There are two cell types: somatic cells and gametes. Somatic cells are all cells that are not gametes (sperm and eggs). The gametes are haploid cells that have only 23 chromosomes and are formed from diploid cells through meiosis.

3. Which statement regarding codons is TRUE? A There are 80 possible codons. B There are three codons that signal the end of a gene. C There are 70 codons that specify amino acids. D Each amino acid has one codon.

B There are three codons that signal the end of a gene, and they are called termination or nonsense codons. There are 64 possible codons, and 61 specify amino acids. There is more than one codon for an amino acid.

16. Regarding sex-linked inheritance, select the true statement. A Most sex-linked traits occur on the Y chromosome. B X-linked recessive diseases are more common than X-linked dominant diseases. C Males are less affected by X-linked diseases. D Females are always homozygous for X-linked traits.

B X-linked recessive diseases are more common than X-linked dominant diseases. Most sex-linked diseases occur on the X chromosome, as the Y chromosome does not carry as many genes. Females are less likely than males to carry an X-linked recessive disease. They have two X chromosomes—one from their mother and one from their father—and, thus, are usually heterozygous for the gene rather than homozygous. Because most X-linked diseases are recessive, females would have to receive two defective chromosomes, which is rare. Males, however, have only one X chromosome, which comes from their mother, and there are no genes on the Y chromosome to counteract that recessive gene; thus, they are more likely to have X-linked recessive genes.

2. The term describing the DNA subunit of one deoxyribose molecule, one phosphate group, and one base is a: A polypeptide. B double helix. C nucleotide. D codon.

C A nucleotide consists of one deoxyribose molecule, one phosphate group, and one base. The double helix is the twisted staircase presentation of DNA that was proposed by Watson-Crick. A polypeptide is a chain of proteins. A codon is a triplet of amino acids.

11. Which is correct regarding Down syndrome? Down syndrome: A occurs in 1 in 400 live births. B produces an individual with a normal IQ. C results in a distinctive facial appearance. D has a symptomatology that includes above average muscle tone.

C Down syndrome, trisomy 21, is one of the best-known examples of aneuploidy, occurring in 1 in 800 live births. Persons with Down syndrome have a distinctive facial appearance with a low nasal bridge, epicanthal folds, protruding tongue, and flat low-set ears. They also have poor muscle tone and short stature. The disease produces mental retardation, with an IQ between 25 and 70 (low).

15. Which statement regarding autosomal recessive trait inheritance is accurate? Autosomal recessive trait inheritance results in: A parents consistently displaying the trait. B approximately 50% of children displaying the trait. C both males and females being affected equally. D the child being heterozygous.

C Males and females are equally affected by autosomal recessive traits. Generally, parents will not display the trait; that is, they are heterozygous themselves, but each will pass the recessive trait to 25% of their children. The child must be homozygous for the trait to express the recessive trait.

4. The function of DNA polymerase is to: A synthesize RNA from the DNA template. B synthesize a polypeptide. C perform base-pairing in replication. D split DNA molecules.

C The function of DNA polymerase is to assist with base-pairing when replicating DNA. This enzyme travels along the single DNA strand, adding the correct nucleotides to the free end of the new strand and proofreading. Transcription is the synthesis of RNA from DNA and uses RNA polymerase. Translation is the formation of a polypeptide from RNA and does not require DNA polymerase.

7. The term describing the sequence for the beginning of a gene is: A intron. B exon. C promoter site. D anticodon.

C The promoter site signals the beginning of a gene and is the location of the RNA polymerase binding. Excised sequences are called introns. Exons are the portions of code that remain after introns are excised, and they code for the actual proteins. The anticodon is the sequence of three nucleotides that undergo complementary base-pairing in translation.

8. Which chemical complex is secreted into the cytoplasm and synthesized in the nucleolus? A Endoplasmic reticulum B Cisternae C Ribosome D Lysosome

C The ribosomes are RNA complexes that are synthesized in the nucleolus and secreted into the cytoplasm, possibly through pores in the nuclear envelope. Cisternae are tubular or saclike channels that extend throughout the cytoplasm. The endoplasmic reticulum is a membrane factory that specializes in synthesis. Lysosomes are saclike structures that originate from the Golgi complex.

12. A female patient born with short stature, webbing of the neck, sparse body hair, and narrowing of the aorta is likely exhibiting symptomatology of: A Klinefelter syndrome. B Down syndrome. C Turner syndrome. D fetal alcohol syndrome.

C Turner syndrome has a karyotype of 45, X. Persons with Turner syndrome are females who are usually sterile, have minimal body hair, and have short stature with a webbed neck. They also have coarctation of the aorta. Down syndrome produces mental retardation, with an IQ between 25 and 70 (low). Persons with Down syndrome have a distinctive facial appearance with a low nasal bridge, epicanthal folds, protruding tongue, and flat low-set ears. They also have poor muscle tone and short stature. Persons with Klinefelter syndrome are male with 47, XXY. The testes are small, body hair is sparse, and the voice is somewhat high pitched. A moderate degree of mental impairment is present. Fetal alcohol syndrome does produce some mental retardation and facial changes; however, there is no webbing of the neck or sparse body hair.

3. Which is a characteristic of Russell-Silver syndrome? A Round moon-shaped face B Tall in stature C Severe mental retardation D Leg length discrepancy

D Russell-Silver syndrome is characterized by growth retardation; proportionate short stature; leg length discrepancy; and a small, triangular-shaped face. About one-third of Russell-Silver syndrome cases are caused by imprinting abnormalities of chromosome 11p15.5 that lead to downregulation of IGF-2 and therefore diminished growth.

5. Which is correct about the epigenetic screening of cancer? A Epigenetic screening is of no use to cancer detection. B Epigenetic screening involves invasive procedures. C This is a very expensive alternative to current testing. D Can complement, or possibly replace, current detection methods.

D The common finding of epigenetic alteration in cancerous tissue raises the possibility that epigenetic screening approaches could complement or even replace existing early detection methods. In some cases, epigenetic screening could be done using bodily fluids, such as urine or sputum, eliminating the need for the more invasive, costly, and risky strategies currently in place.

13. A patient born with the deletion of the short arm of the chromosome 5 is exhibiting a characteristic of: A Down syndrome. B Turner syndrome. C fragile X syndrome. D cri du chat syndrome.

D This patient most likely will have cri du chat syndrome. This is the most often cited example of a chromosomal deletion-in this case, chromosome 5. Turner syndrome affects the sex chromosomes of females. Down syndrome is an example of aneuploidy. Fragile X syndrome develops due to a break or gap on the X chromosome; thus, the term "fragile sites." These patients may not manifest any disease, but may pass it on to their offspring.

6. Base pairs are appropriately described as: A adenine pairs with guanine. B guanine pairs with thymine. C cytosine pairs with adenine. D uracil pairs with adenine.

D Uracil is structurally similar to thymine. Therefore, the correct base-pairs are adenine with thymine, guanine with cytosine, and uracil with adenine.