Midterm Exam Review HW Flashcards
Would any sort of insertion or deletion be cosnidered epigenetic?
No! Insertions and deletions in teh DNA sequence are permanent and therefore not considered epigenetic.
allele
different versions/variations of the same gene
Homologous recombination is suppressed near centromeres and increases greatly near telomeres in both males and females (but more so in males)
True or False?
True
Which type of condition is associated with all of hte following symptoms?
- congenital heart defects
- polydactyly
- retinal degeneration
- cystic kidneys
- brain anomalies
ciliopathies
What type of caridac condition is NOT associated with ciliopathies?
cardiac arrythmias
Homologous recombination facts
- occurs in meiosis 1
- recombination nusually involves one or more chiasmas per chromosome arm
- females have more recombination events than males
- different autosomes have different number of chiasmas beccuase they are different lengths and have different number of genes
- recombination is suppressed near centromeres and increases greatly near telomeres in both males and females (but more so in males)
Genome-wide epigenetic reprogramming in fetal development occurs in two waves. In the first wave of epigenetic reprogramming at about 8 days embryonic cells undergo genome-wide demethylation. Are imprinting centers included in this reprogramming?
No.
Imprinting centers are excluded from this stage of reprogramming.
What is a nonsense variant?
Point mutation in a DNA sequence that causes the replacement of the normal codon for an amino acid by one of the three termination (or “stop”) codons creates a nonsense variant or premature termination codon (PTC; also called stop gain). This causes translation to stop prematurely.
What is the most common outcome of a nonsense variant?
In general, mRNAs harboring a PTC (premature termination codon) are targeted for rapid degradation through a cellular process known as nonsense-mediated mRNA decay (NMD), and no translation is possible.
disease causing b/c not enough protein created?
What is a possible, but less likely, result of a nonsense variant?
Rarely, transcripts harboring a PTC (premature termination codon) escape NMD (nonsense-mediated mRNA decay), most predictably if the premature stop codon occurs in last 50bp of the penultimate exon or anywhere in the final exon of a gene. In this circumstance, a nonsense mutation can often give rise to a truncated protein with altered function.
What is c.434 C>T (p.R115X)
Emailed Dr. Tallis about this. Not sure if p is describing the protein or mRNA b/c it doesn’t really make sense.
What is nonsense mediated mRNA decay (NMD)?
a cellular mechanism to prevent translation into truncated proteins by recognizing and degrading mRNAs carrying premature translation termination (nonsense) condons. In general mRNAs hoboring a PTC (premature termination codon) are targeted for rapid degradation through a celular process known as NMD. This results in complete absence of protein.
Assume that 500,000 serial newborns were examined for new mutation cases of a dominant disorder with 100% penetrance. Twenty affected infants were found with unaffected parents. What is the calculated mutation rate?
2 x 10-5
A couple are both carriers for an autosomal recessive disorder. They have 3 children. What is the probabililty that at least one child is affected?
37/64
probability of each child not being affected: 3/4 x 3/4 x 3/4 = 27/64
1 - 27/64 = 37/64
Name the 5 acrocentric chromosomes.
13, 14, 15, 21, 22
Acrocentric chromosomes contain tandem repeats of ribosomal DNA.
True or False?
True
What does facultative mean?
- occurring optionally in response to circumstances rather than by nature
- capable of but not restricted to a particular function or mode of life
What is heterochromatin?
Condensed DNA that stains darkly. Regions such as centromeres, acrocentric short arms, and portions of human chromosomes 1, 9, 16, and Y constitute constitutive heterochromatin and are relatively genetically inactive in all cells
What is facultative heterochromatin?
Facultative heterochromatin is a variable feature, exemplified by the inactive X chromosome (Barr bodies). Contrast with euchromatin.
Another example is the p arm of acrocentric chromsomes.
You are seeing a patient in clinic with bilateral congenital sensorineural hearing loss. Which of the
following conditions would NOT be on your differential?
A. Usher syndrome
B. Alport syndrome
C. Pendred syndrome
D. Waardenburg syndrome
B. Alport syndrome (b/c typically causes progressive hearing loss, not congenital)
The others all cause congenital hearing loss.
A 24-year-old woman is a known carrier of autosomal recessive phenylketonuria, and has an
affected brother. She and her partner are half-first cousins (their mothers are paternal half-sisters), and
they are expecting their first child. There is no further family history of phenylketonuria. Which of the
following is the chance for the couple to have a child with phenylketonuria?
I think this is wrong. Shouldn’t the risk for the sister of the affected person be 2/3?
Core promoter elements that direct transcription include…
CAAT box and CpG islands
What is the target for DNA methylation?
CpG islands are targets for DNA methylation
always 5’CpG3’
Which is more rare? A mosaic variant in a parent (gonadal mosaicism) or a mosaic variant in a child.
gonadal mosaicism 1-2%
somatic mosaicism that is throughout the body, so happened early in development, is VERY rare. More rare than gonadal mosaicsim.
