Chromosomal Abnormalities Flashcards
What is the normal male karyotype?
46XY
What stain is used for G-banding?
Giemsa stain
What is a telomere and what is its function?
- DNA + protein cap
- Ensures DNA replication to tip
- Tether to nuclear membrane
What are light bands?
- Less condensed chromatin
- Transcriptionally active
- Gene + GC rich
What is the function of centromeres?
- Joins sister chromatids
- Essential for chromosome segregation at cell division
What are dark (G) bands?
- Condensed chromatin
- Gene poor, AT rich
What is Cytogenetic testing?
G banded routine karyotype
Karyotype = test of whole genome but normal result does not exclude genetic problem
What gene is CF, Huntington’s and SCA on?
CF = gene 7 Huntington's = gene 4 SCA = gene 11
What is the limit of detection of Karyotype resolution?
Able to see changes (e.g. deletion or extra piece) down to 5 million bases = limit, won’t see any smaller
What is DNA sequencing used for?
To look at DNA one base at a time
Name some cytogenetic techniques
Karyotype, FISH, Array-CGH
Name some molecular genetic techniques
MLPA, DNA sequencing
What is a Karyotype and what is the standard notation?
Karyotype = representation of person’s chromosome complement
Standard notation:
- total no. chromosomes
- followed by sex chromosome composition
- followed by any abnormalities detected
- changes in whole chromosome number (= chromosomal aneuploidy) = denoted using + or - sign against particular chromosome
Are trisomies viable?
No, common at conception only, never born
What is the only chromosomal monogamy survivable to term?
Turner syndrome (monosomy X)
What is a common mechanism of chromosomal aneuploidy?
Non-disjunction at meiosis (can occur in meiosis I or II)
What is Down syndrome?
Trisomy 21 - most common autosomal trisomy
How is Down syndrome detected?
- Structural abnormalities in antenatal scans, screening tests, or facial appearance at birth
- Increased nuchal translucency measurement @ 12 weeks
What is the presentation of Down syndrome in infants?
- muscle hypotonia
- large tongue
- umbilical hernia
- brush field spots
- single player crease
- congenital defects