Lecture 18: Pre-Implantation Genetic Screening and Diagnosis

Question 1

What is PGD? What does it do?

Answer 1

Pre-Implantation Genetic Diagnosis

- technique to identify genetic defects in embryos created through IVF BEFORE implantation

Question 2

What is PGS? What does it do?

Answer 2

Pre-Implantation Genetic Screening

- Embryos from normal genetic parents are screened for defects

Question 3

What are the 3 major group of diseases regarding PGS/PGD?

Answer 3

1) Chromosomal Disorders
2) Single Gene Defects
3) Sex-linked disorders

Question 4

What is an example of Chromosomal Disorder?

Answer 4

Down Syndrome

Question 5

Karyotyoes are prepared from ______ cells that have been arrested in ___phase portion of the cell cycle, when ____ assume their most condensed conformations

Answer 5

mitotic
meta(phase)
chromosomes

Question 6

Normal compliment of chromosomes, exact multiple of haploid numbers, 2n (46 chromosomes) is:

Answer 6

Euploidy

Question 7

Abnormal number of chromosomes is:

Answer 7

Aneuploidy

Question 8

3 complete sets of chromosomes, 3n (69 in humans) is:

Answer 8

Triploidy

Question 9

Presence of additional (third) chromosome of one type in otherwise Diploid cell (2n+1)

Answer 9

Trisomy

Question 10

Cell Cycle Review:

The cell “double checks” the duplicated chromosomes for error, making any needed repair

Answer 10

G2

Question 11

Cell Cycle Review:

Cellular contents, excluding the chromosomes, are duplicated

Answer 11

G1

Question 12

Cell Cycle Review:

Each of the 46 chromosomes is duplicated by the cell

Answer 12

S

Question 13

Cell Cycle Review:

Cell cycle arrest

Answer 13

G0

Question 14

Fixation of cells for cyrogenetics is:

Answer 14

Metaphase

Question 15

Nuclear Division is:

Answer 15

Karyokinesis

Question 16

Cytoplasm division is:

Answer 16

Cytokinesis

Question 17

Whats the process of mitosis between G2 and G1

Answer 17

Prophase, Prometaphase, Metaphase, Anaphase, Telephase, Cytokinesis

Question 18

First polar body extruded prior to______

Second polar body extruded after______

Answer 18

Ovulation

Fertilization

Question 19

What is the 6 step process of PGS/PDG

Answer 19

1) Genetic Counseling
2) IVF with ICSI
3) Biopsy
4) Genetic Testing
5) Transfer of “unaffected” embryo
6) Advise against intercourse during IVF cycle

Question 20

Polar Body Biopsy:

First (and/or Second) polar bodies are removed using ________ and _______

Answer 20

micromanipulator

microscope

Question 21

Polar Body Biopsy:

Can only detect female chromosomal disorders because:

Answer 21

• gives indirect information about whether genetic defect is present in oocyte
• Chromosomal abnormalities occurring after fertilization are not detected
• Technique is infrequently used due to limitations

Question 22

Polar Body Biopsy:

Samples extra-embryonic material because:

Answer 22

• Less likely to affect subsequent embryo development

- May be ethically preferable to some (when embryo screening is not permitted)

Question 23

Blastomere Biopsy:

Goal is to remove one (or two) ____ cell(s) with minimal _____ to remaining embryo

Answer 23

Intact

trauma

Question 24

Blastomere Biopsy:

Embryo is cultured in calcium and magnesium free medium because:

Answer 24

• Reduces blastomere-to-blastomere adherence

- Facilitates blastomere removal

Question 25

Blastomere Biopsy:

Single blastomere is removed using micromanipulator and microscope because:

Answer 25

• Second blastomere may also be removed to confirm results from first blastomere

Question 26

What is the goal of Trophectoderm Biopsy:

Answer 26

remove 5-10 cells with minimal trauma to reaming embryo

Question 27

What is “FISH?”

Answer 27

Fluorescence in situ hybridization

Question 28

What are some examples of “Current Technology?”

Answer 28

• Whole genome sequencing

- Single-gene testing

Question 29

What does FISH accomplish?

Answer 29

• Probes are small pieces of DNA matched for chromosomes being analyzed
• Each probe is labeled with different fluorescent dye
• Fluorescent probes are applied to biopsy sample
• Probes can be seen under microscope

Question 30

FISH can only analyze about __chromosomes at most for a ____ cell, by this method

Answer 30

10; single

Question 31

What 9 chromosomes does FISH detect?

Answer 31

X, Y, 13, 15, 16, 18, 21, 22

Question 32

FISH is performed in ___ rounds on _____ nucleus

Answer 32

2; blastomere

Question 33

What are 2 test that fall under current technology?

Answer 33

PGS and PGD

Question 34

What is PGS and what does it accomplish?

Answer 34

Whole-genome sequencing

• Screens all 24 chromosomes simultaneously
• 22 autosomal and X and Y
• Detects aneuploidy

Question 35

What is PGD and what does it accomplish?

Answer 35

Single-gene testing

• Detects single gene mutations
• Requires mutation analysis for both parents

Question 36

Transfer of “unaffected” embryos:

Genetic/ Chromosome testing can be completed within ____/_____

Answer 36

24 hours; 1 week

Question 37

Transfer of "unaffected" embryos:
Blastomere biopsy ( from Day \_\_ embryo) may permit \_\_\_\_\_ of \_\_\_\_\_\_\_ (day \_\_ embryo)

Answer 37

03; transfer; blastocyst; 05

Question 38

Transfer of “unaffected” embryos:

_____ biopsy requires _____ of blastocyst

Answer 38

Trophectoderm; freezing

Question 39

What is mosaicism

Answer 39

• presence of two populations of cells with different genotype in one individual who has developed from a single fertilized egg
• may result from mutation during meiotic or mitotic cell division

Question 40

During mosaicism, when does self-correction occur?

Answer 40

• Euploid cells proliferate faster than aneuploidy cells

- Mosaic embryos may halt proliferation of abnormal cells or exclude abnormal cells