Cytogenetics

Question 1

What is the G-banding pattern in a chromosome?

Answer 1

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

Question 2

What type of chromosome are only involve in robertsonian translocation?

Answer 2

Acrocentric chromosomes

Question 3

What could you think to be the cause of mental retardation or pregnancy loss?

Answer 3

Chromosome abnormalities

Question 4

Why does the Down syndrome patients have high incidence of Alzheimer disease?

Answer 4

Developed by 5th or 6th decade of life, amyloid precursor protein (APP) gene in chromosome 21

Question 5

Most common chromosome abnormality causing spontaneous loss of pregnancy

Answer 5

Trisomy

Question 6

Named examples of mosaicism

Answer 6

• Turner syndrome

-

Question 7

What is the triple screen and for what is used?

Answer 7

• Alfa-fetoprotein, chorionic gonadotropin, unconjungated estriol
• detect approximately 70% fetuses with Down syndrome (prenatal diagnosis)

Question 8

Difference of structural chromosome abnormality in germ line and somatic cells

Answer 8

• germ line: segregate to the offspring

- somatic cell: ⬆️ risk of cancer (no pass to the offspring)

Question 9

What is a reciprocal translocation?

Answer 9

When part or piece of chromosomes are exchanged between no homologous ones (translocation carrier)

Question 10

Which is the problem to be a translocation carrier, does it have symptoms or disease?

Answer 10

• 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

Question 11

What is consequence of an alternate segregation in a reciprocal translocation?

Answer 11

• normal haploid gamete ▶️ diploid conception
• live born phenotypically normal translocation carrier
• gametes from translocation carrier contain balanced chromosomal material

Question 12

What is the consequence of an adjacent segregation in a reciprocal translocation?

Answer 12

• unbalanced genetic material and most likely loss of pregnancy
• gametes that contain unbalanced chromosomal material produce conceptions with partial monosomies and trisomies

Question 13

What is the cause of the Philadelphia chromosome? What is the consequence?

Answer 13

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

Question 14

What is a robertsonian translocation?

Answer 14

• two non homologous chromosomes without short arms, fusion their long arms

Question 15

Do a robertsonian translocation carrier have clinical consequences or symptoms?

Answer 15

No because short arms of acrocentric chromosomes don’t contain essential information

Question 16

What type of segregation must occur in robertsonian translocation to get normal diploid and translocator carrier?

Answer 16

Alternate segregation

Question 17

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?

Answer 17

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)

Question 18

How can you differentiate the cause of Down syndrome by non disjunction (95% of the cases) or robertsonian translocation (5%)?

Answer 18

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)

Question 19

What is the result of a adjacent segregation in a robertsonian translocation?

Answer 19

• unbalanced information is transmitted and loss pregnancy results, except if chromosome 21 is involved, trisomy 21 occur.

Question 20

Which is a structural chromosome abnormality cause of cri-du-chat syndrome?

Answer 20

Interstitial and terminal deletion of 5p chromosome

Question 21

What other chromosomal structural abnormality besides aneuplody (by non disjunction) results in Turner syndrome?

Answer 21

Ring chromosome

Isochromosome

Question 22

What is the advantage of FISH respect classic karyotype?

Answer 22

The chromosome don’t have to be in metaphase stage for accurate diagnosis
*aneuplidies, translocations, deletions (include microdeletion)

Question 23

Which are the most common chromosomal abnormalities associated with spontaneous abortion?

Answer 23

1. Trisomy (52%), all, but 16 most common
2. Polyploidy (22%)
3. Monosomy (19%)