Genetic Diagnosis

Question 1

use of agarose gel electrophoresis of PCR products?

Answer 1

if known mutation changes the length of the gene, this difference can be detected in the PCR-amplified DNA by electrophoresis on agarose gel

Question 2

how does the blotting technique work? breaking down of DNA, charge, what do you add?

Answer 2

DNA broken down using restriction endonucleases = DNA fragments - RNA and proteins not cut up, they are small enough to analyze directly
DNA and RNA negatively charged so migrate towards positive terminus on basis of size
add specific probes

Question 3

what does southern block analyze?

Answer 3

analyzes DNA fragments on a gel electrophoresis using a probe

Question 4

what does northern blot analyze?

Answer 4

analyzes RNA fragments on a gel electrophoresis using a probe

Question 5

what does western blot analyze?

Answer 5

analyzes proteins on gel electrophoresis using enzyme linked antibody

Question 6

what does dot blot analyze and what is it used for?

Answer 6

analyzes RNA, DNA or proteins and does not use electrophoresis

Question 7

most often, how will mutated alleles differ?

Answer 7

differ in fragment size b/c a SNP will delete a palindrome that is normally present on a normal allele

Question 8

genetics of sickle cell anemia? chance of being a carrier vs having the dz?

Answer 8

normally there are 3 palindromes in the beta-globin allele
A to T SNP destroys the palindrome at the restriction site for MST II
fetus has 50% chance of being carrier, 25% chance of having the dz
can tell for sure with RFLP analysis

Question 9

what does northern blot specifically measure and what can it be used to determine?

Answer 9

measures mRNA and it’s levels

used to determine pattern of expression in organs cell types and how much

Question 10

what is an allele-specific oligonucleotide? what does it act as? why are they put onto chips?

Answer 10

short piece of synthetic DNA complementary to the sequence of a variable target DNA
it acts as a probe for the presence of the target in a southern assay or more commonly, in the simpler dot blot assay
put onto chips for specific disease testing

Question 11

how are DNA chips used?

Answer 11

ASOs (allele specific oligonucleotides) are put onto chips for specific dz testing
thousands of different oligonucleotides, representing various mutations and normal sequences are embedded on a silicone chip
pt DNA from specific regions is amplified by PCR, tagged with a fluorescent label and exposed to the oligonucleotides on the chip
it is a type of dot blot and can be used to test for RNA and proteins

Question 12

what is indirect genetic diagnosis? what does it use? what marker is most likely used?

Answer 12

if mutation causing a dz in a family is not known, indirect analysis can be used to infer if a parent has transmitted the mutation to their offspring
uses genetic markers that are closely linked to the diseased locus
STRPs are most commonly used b/c they have multiple alleles - often used as informative markers to use

Question 13

what are the 5 applications of genetic diagnosis/

Answer 13

carrier dx in recessive dz
presymptomatic diagnosis fro late-onset dzs
asx diagnosis for dzs w/reduced penetrance
prenatal dx
preimplantation testing

Question 14

what is one of the most common applications of genetic dx?

Answer 14

prenatal genetic diagnosis

Question 15

fetal cells present in amniotic fluid can be used to dx what? risk of amniocentesis?

Answer 15

single gene d/os
chromosome abnormalities
some biochemical d/os (alpha-fetoprotein levels in NTD)
risk of fetal demise is 0.5% in amniocentesis

Question 16

when can chorioinic villus sampling be completed? what does it involve, how can it be done? what does it provide? associated mortality rate?

Answer 16

can be completed at 10-12 wks gestation
involves removal of a sm sample of chorionic villus material
can be done either transcervical or transabdominal
provides dx earlier in PG
have a higher fetal mortality rate of 1% and can have sm diagnostic error b/c of placental mosaicism

Question 17

what is panorama?

Answer 17

cfDNA testing that can be completed at 9 weeks and tests for numerical abnormalities

Question 18

how is preimplantation diagnosis done? when is it done?

Answer 18

embryos derived from in vitro fertilization can be dx by removing a single cell
typically taken from eight-cell stage
DNA is PCR amplified and is used to make a genetic diagnosis - allows PG to be terminated so that only embryos w/o mutations are implanted
disadvantage is potential diagnostic error as a result of a PCR amplification from a single cell

Question 19

what is Beckwith-Wiedemann syndrome? what does it put children at risk for?

Answer 19

overgrowth d/o usu present at birth characterized by an increased risk of childhood cancer and certain congenital features, also observed severe increase in size of the adrenal glands

Question 20

original name of Beckwith-Wiedemann syndrome?

Answer 20

originally exomphalos-macroglossia-gigantism syndrome to combine the combo of congenital abd wall defects of hernia, large tongue and large bodies and/or limbs

Question 21

5 common features of BWS?

Answer 21

macroglossia
macrosomia
midline abd wall defects
ear creases or ear pits
neonatal hypoglycemia