Cytogenetics Flashcards
What is the G-banding pattern in a chromosome?
Is the staining of a chromosome in a karyotype, revealing a light and dark regions (G-bands), allowing the chromosomes to be accurately identified.
*occur because trypsin digest partially some associated protein to the chromosomes ▶️ giemsa binds to DNA
What type of chromosome are only involve in robertsonian translocation?
Acrocentric chromosomes
What could you think to be the cause of mental retardation or pregnancy loss?
Chromosome abnormalities
Why does the Down syndrome patients have high incidence of Alzheimer disease?
Developed by 5th or 6th decade of life, amyloid precursor protein (APP) gene in chromosome 21
Most common chromosome abnormality causing spontaneous loss of pregnancy
Trisomy
Named examples of mosaicism
- Turner syndrome
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What is the triple screen and for what is used?
- Alfa-fetoprotein, chorionic gonadotropin, unconjungated estriol
- detect approximately 70% fetuses with Down syndrome (prenatal diagnosis)
Difference of structural chromosome abnormality in germ line and somatic cells
- germ line: segregate to the offspring
- somatic cell: ⬆️ risk of cancer (no pass to the offspring)
What is a reciprocal translocation?
When part or piece of chromosomes are exchanged between no homologous ones (translocation carrier)
Which is the problem to be a translocation carrier, does it have symptoms or disease?
- don’t have symptoms or clinical consequences (have balanced, although misplaced the genetic information)
- problem is during gametogenesis and meiosis unbalanced genetic material can be transmitted to the offspring
What is consequence of an alternate segregation in a reciprocal translocation?
- normal haploid gamete ▶️ diploid conception
- live born phenotypically normal translocation carrier
- gametes from translocation carrier contain balanced chromosomal material
What is the consequence of an adjacent segregation in a reciprocal translocation?
- unbalanced genetic material and most likely loss of pregnancy
- gametes that contain unbalanced chromosomal material produce conceptions with partial monosomies and trisomies
What is the cause of the Philadelphia chromosome? What is the consequence?
Reciprocal translocation of the long arms of chromosomes 9 and 22
- alters activity of the abl protooncogene (break middle of gene)
- when occur in hematopoietic cells ▶️ chronic myelogenous leukemia
What is a robertsonian translocation?
- two non homologous chromosomes without short arms, fusion their long arms
Do a robertsonian translocation carrier have clinical consequences or symptoms?
No because short arms of acrocentric chromosomes don’t contain essential information
What type of segregation must occur in robertsonian translocation to get normal diploid and translocator carrier?
Alternate segregation
In a context of a couple with a son or daughter with Down syndrome and multiple loss of pregnancy, what is the most possible genetic cause?
Robertsonian translocation in one of the parents
*5% of Down syndrome is because robertsonian translocation, but have higher recurrence rate than non disjunction cause (10-15% mom carrier, 1-2% dad carrier)
How can you differentiate the cause of Down syndrome by non disjunction (95% of the cases) or robertsonian translocation (5%)?
Examining the karyotype: key difference 47 vs 46 chromosomes
- non disjunction: 47XX+21, or 47XY+21
- robertsonian translocation: 46XX-14+t(14q;21q), or 46XY-14+t(14q;21q)
What is the result of a adjacent segregation in a robertsonian translocation?
- unbalanced information is transmitted and loss pregnancy results, except if chromosome 21 is involved, trisomy 21 occur.
Which is a structural chromosome abnormality cause of cri-du-chat syndrome?
Interstitial and terminal deletion of 5p chromosome
What other chromosomal structural abnormality besides aneuplody (by non disjunction) results in Turner syndrome?
Ring chromosome
Isochromosome
What is the advantage of FISH respect classic karyotype?
The chromosome don’t have to be in metaphase stage for accurate diagnosis
*aneuplidies, translocations, deletions (include microdeletion)
Which are the most common chromosomal abnormalities associated with spontaneous abortion?
- Trisomy (52%), all, but 16 most common
- Polyploidy (22%)
- Monosomy (19%)
