Genetics Flashcards
Which one of the following statements in correct regarding DNA?
A. Consists of nucleotides adenosine, cytosine, guanine and uracil
B. Is translated to generate messenger RNA
C. Topoisomerase generates a new copy from a template of DNA
D. DNA expression is increased by DNA cytosine methylation
E. Oxidative damage by ionising radiation can lead to double strand DNA breaks
Answer: E - Oxidative damage by ionising radiation can lead to double strand DNA breaks
Wilson disease has a frequency of 1 in 8100 in a community. What is the carrier rate?
A. 1 in 90 B. 1 in 15 C. 89 in 90 D. 1 in 45 E. 1 in 60
Answer: D - 1 in 45
Hardy Weinberg equilibrium:
a^2 + 2aA + A^2 = 1
Alternatively divide by 4 and square root
Which one of the following statement is FALSE regarding RNA?
A. HIV is a single stranded RNA virus
B. MicroRNAs are post-transcriptional regulators that target messenger RNA transcripts (mRNAs) for repression or degradation
C. Viruses use reverse transcriptase to generate DNA molecules from RNA
D. Transfer RNA (tRNA) is a small RNA chain that transfers a specific amino acid to a growing polypeptide chain during translation
E. Ribosomes are the site of RNA synthesis
Answer: E - Ribosomes are the site of RNA synthesis (is false)
Which one of the following processes is involved in the inactivation of the second X chromosome (Barr body) in females?
A. DNA hypomethylation B. DNA hypermethylation C. Increased histone acetylation D. Chromosomal translocation E. Decreased expression of non-coding RNAs
Answer: B - DNA hypermethylation
DNA methylation is the addition of methyl groups to inactivate transcription of the affected genes. Hypermethylation occurs during inactivation of the second X chromosome in females (lyonisation). The inactive X Chromosome has high levels of DNA methylation, low levels of histone acetylation with gene silencing.
Which one of the following describes mature messenger RNAs correctly?
A. Mature mRNAs are created by post-transcriptional processing
B. The production of protein from mature mRNA is called transcription
C. Mature mRNAs are generation from introns
D. Adenine, cytosine, guanine and thymine are the nucleotide bases found in mature mRNA
E. Mature mRNA is degraded by ribosomes
Answer: A - Mature mRNAs are created by post-transcriptional processing
Which one of the following is a feature of mitochondrial DNA disorder inheritance?
A. Paternal gene transmission
B. Autosomal dominant inheritance
C. Point mutation is the type of defect identified in all mitochondrial gene mutations
D. There is a single copy of mitochondrial DNA in each cell
E. A mitochondrial gene mutation is present only in a proportion of the cell’s mitochondrial genome copies
Answer: E - A mitochondrial gene mutation is present only in a proportion of the cell’s mitochondrial genome copies
Mitochondria have their own chromosomes and are passed from a mother to all of her children, but not from the father. There is a high and variable number of NDA copies. Due to this heteroplasmy, a mitochondrial mutation may be present in only a proportion of the mitochondrial genome copies.
Which one of the following statements about single-nucleotide polymorphisms (SNPs) is correct?
A. SNPs occur more frequently in coding regions than non-coding regions
B. SNPs within a coding sequence always change the amino acid sequence of the protein produced
C. SNPs that are not in protein-coding regions do not affect gene expression
D. A SNP allele occurs at the same frequency across all human populations
E. A SNP may cause a disease with Mendelian inheritance
Answer: E - A SNP may cause a disease with Mendelian inheritance
Which one of the following statements concerning familial adenomatous polyposis (FAP) is correct?
A. Testing of the adenomatous polyposis coli (APC) gene is cost-effective in identifying carriers of the APC mutation among at-risk relatives of affected individuals
B. 1st degree relatives should be screened with DNA sequencing of p53
C. Affected persons develop colorectal adenocarcinoma after the age of 30years
D. FAP is an autosomal recessive condition
E. Patients identified with mutations should have colonoscopy every 3 years
Answer: A - testing of the adenomatous polyposis coli (APC) gene is cost-effective in identifying carriers of the APC mutation among at-risk relatives of affected individuals
FAP is an autosomal dominant disorder with almost universal penetrance i.e. colorectal cancer by the age of 40. Mean age of death is 42 years. Testing is cost effective to identify carriers in at risk relatives.
Early diagnosis increased life expectancy throughout improved surveillance and timely prophylactic colectomy.
Patients with an APC mutation should have:
- Annual colonoscopy
- As progresses, often by late teens-20s there are too many polyps to safely remove and then prophylactic subtotal colectomy is recommended
- Still requires annual endoscopy screening due to risk of gastric cancer and upper GI adenomas
A 25 year old Cambodian woman who is known to have mild and non-symptomatic anaemia associated with beta-thalassemia trait presents for genetic counselling. She is about to marry a 28 year old Cambodian man with no symptoms but also found on recent testing to have beta-thalassemia trait. Which one of the following is the probability that they will have an unaffected child without either B-thalassemia or trait.
A. 0.01 B. 0.1 C. 0.25 D. 0.5 E. 0.75
Answer: C - 0.25
Which one of the following changes in genomic stability contributes to the development of colorectal cancer?
A. Chromosomal instability involves inactivation of genes required for repair of mismatches in DNA bases
B. Chromosomal instability causes the loss of a wild-type copy of APC, a tumour suppressor gene
C. Germline defect in mismatch-repair genes is the main explanation for FAP
D. Amplification of gene copy numbers occurs commonly in colorectal cancer
E. Gene rearrangement occurs commonly in colorectal cancer
Answer: B - Chromosomal instability causes the loss of a wild-type copy of APC, a tumour suppressor gene
Loss of genomic stability can drive colorectal cancer and facilitate acquisition of multiple tumour causing genetic mutations.
The most common type of genetic instability in CRC is chromosomal instability, which cause changes in Chromosomal copy number and structure. Chromosomal instability is an efficiency mechanism for casing the loss of wild type tumour suppressor genes (i.e. APC, p53, SMAD) which oppose the malignant phenotype.
In a subgroup of CRC, there is inactivation of genes for DNA mismatch-repair. Inherited inactivation = HNPCC/Lynch syndrome. Germline defects in mismatch-repair genes (primarily MLH1 and MSH2) confer a lifetime risk of CRC of 80%, most by age of about 45yrs.
Which one of the following is correct regarding Down syndrome?
a. Alzheimer-like changes in the brain develop in mid-life
B. Both males and females are infertile
C. Temporal lobe epilepsy occurs in 40%
D. The commonest chromosomal abnormality is translocation
E. Individuals have a higher risk of developing acute myeloid leukaemia but not acute lymphoblastic leukaemia.
Answer: A - Alzheimer-like changes in the brain develop in mid-life
T21 - most non-dysjunction during meiosis
Remaining 5% have Robertsonian translocation or mosaicism
Risk of ALL is 10-20x increased.
A 36 year old man has paraesthesiae in his hands and feet. On examination, he has diffuse cutaneous angiokeratomas, which are particularly predominant on the buttocks, upper thighs, lower abdomen and peri-umbilical area. He has a systolic murmur in the aortic area. Echocardiography reveals asymmetrical left ventricular hypertrophy and LVOT obstruction. What is the most likely diagnosis?
A. Fabry disease B. Neurofibromatosis C. Niemann-Pick disease D. Tay-Sachs disease E. Marfan syndrome
Answer: A - Fabry disease
X-linked lyosomal storage disease. Alpha-galactosidase A deficiency
Which one of the following disease exhibits genetic anticipation?
A. Familial hypercholesterolaemia B. Friedrich ataxia C. Myotonic dystrophy D. Tuberous sclerosis E. Von Willebrand disease
Answer: C - Myotonic dystrophy
Genetic anticipation refers to the increasing severity and earlier age of onset of disease in successive generations.
Commonly with trinucleotide repeat disorders including Huntington disease, fragile X syndrome, spinocerebellar ataxia and myotonic dystrophy
Which one of the following correctly describes the haemochromatosis (HFE) gene and iron-overload disease?
A. HFE gene mutation in hereditary haemochromatosis type 1 is inherited in an autosomal dominant manner
B. H63D mutation homozygotes are a common >90% finding in individuals with HH
C. C282Y mutations homozygotes develop iron-overload disease before 30yrs age
D. HFE gene mutations can lead to impairment in the hepcidin-ferroportin axis
E. Disease penetration in homozygotes for C282Y mutation is high >75%
Answer: D - HFE gene mutations can lead to impairment in the hepcidin-ferroportin axis
Nearly 10% of the white population carries the C282Y HFE mutation. Inheritance of haemochromatosis in an autosomal recessive manner with variable expressivity.
A 22 year old woman is referred for review because her 50yr old father is diagnosed with Huntington disease. She wants to know what this means for her. What is the most appropriate information?
A. She may have inherited the gene for Huntington disease but it manifests in men only
B. There is a 50% chance that she has inherited the gene and if she has, will likely develop symptoms at a younger age than her father
C. There is a 50% chance she inherited the gene and if she has, she is likely to develop symptoms at a later age.
D. There is a 50% chance that she has inherited the gene for Huntington disease, but fewer than half develop disease
E. She is a carrier of the gene for Huntington, but is unlikely to develop disease herself unless it runs in her mother’s family
Answer: B - There is a 50% chance that she has inherited the gene and if she has, will likely develop symptoms at a younger age than her father
Autosomal dominant CAG repeat disorder.
Causes triad of progressive: 1. motor, 2. cognitive and 3. psychiatric symptoms
Anticipation is more common with paternal transmission of the disease allele.
