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Lecture 5

BIMS 201 Lecture Notes - Lecture 5: Robertsonian Translocation, Spina Bifida, Neural Tube Defect

Biomedical Science
Course Code
BIMS 201
Elizabeth A.Crouch

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Case Study #3 Discussion-Down Syndrome
Robertsonian translocation: carried in fam
o Typically b/w acrocentric chroms.
o Switching q arms do’t pair ell durig prophase I eiosis I
End up w/cross structure
Carriers (45 chroms.) lose p arms on 14p-21 p chrom.: EXP no phenotype
except very easily have Downs offspring
Balance translocation
½ of children will die
o 50:50 chance a pregnancy will survive
1/3 of children will have Downs
13 (acrocentric), 18, and 21 typically survive as trisomies
Polymerase Chain Rxn (PCR)
o Amplifies DNA, crime scene analysis, detects presence/absence of genetic
o 3 steps
denature: pulls DNA apart, primers and synthesis (always ’ ’
up to 90C
anneal: lower temp. to anneal primers
extension: Taq polymerase; temp. raised for this enzyme
o can control specificity w/primers, length of primers, and temps.
RT-PCR: real time PCR
o Allows direct observation
o Measures throughout cycles
o Quantifies mRNA in a cell
o Diagnose trisomy 21 by looking @ gene EXP of mRNA
o Works w/reverse transcriptasenucleotides tagged w/fluorescent molecs. and
can quantify amt. of mRNA in cell
o Tells you what and how much of something is being EXP/made (bc of mRNA)
o 4 steps
o intensity of fluorescents can be quantified
AFP: produced by fetal liver and INC in pregnancy
o High levels indicate neural tube defect (anencephaly, spina bifida, etc.)
o Lower levels indicate Downs
o Diagnostics
False + : pregnant w/multiples, baby has mutation in AFP production (low
Out of 5 markers, ambiguous results
Why test in a 16-week fetus: age indication, familial Downs, baby is still
very small
Older they get, can > easily prick them w/needle
Mother still has decision points and still legal to have abortion
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