Lecture 18: Pre-Implantation Genetic Screening and Diagnosis Flashcards
What is PGD? What does it do?
Pre-Implantation Genetic Diagnosis
- technique to identify genetic defects in embryos created through IVF BEFORE implantation
What is PGS? What does it do?
Pre-Implantation Genetic Screening
- Embryos from normal genetic parents are screened for defects
What are the 3 major group of diseases regarding PGS/PGD?
1) Chromosomal Disorders
2) Single Gene Defects
3) Sex-linked disorders
What is an example of Chromosomal Disorder?
Down Syndrome
Karyotyoes are prepared from ______ cells that have been arrested in ___phase portion of the cell cycle, when ____ assume their most condensed conformations
mitotic
meta(phase)
chromosomes
Normal compliment of chromosomes, exact multiple of haploid numbers, 2n (46 chromosomes) is:
Euploidy
Abnormal number of chromosomes is:
Aneuploidy
3 complete sets of chromosomes, 3n (69 in humans) is:
Triploidy
Presence of additional (third) chromosome of one type in otherwise Diploid cell (2n+1)
Trisomy
Cell Cycle Review:
The cell “double checks” the duplicated chromosomes for error, making any needed repair
G2
Cell Cycle Review:
Cellular contents, excluding the chromosomes, are duplicated
G1
Cell Cycle Review:
Each of the 46 chromosomes is duplicated by the cell
S
Cell Cycle Review:
Cell cycle arrest
G0
Fixation of cells for cyrogenetics is:
Metaphase
Nuclear Division is:
Karyokinesis
Cytoplasm division is:
Cytokinesis
Whats the process of mitosis between G2 and G1
Prophase, Prometaphase, Metaphase, Anaphase, Telephase, Cytokinesis
First polar body extruded prior to______
Second polar body extruded after______
Ovulation
Fertilization
What is the 6 step process of PGS/PDG
1) Genetic Counseling
2) IVF with ICSI
3) Biopsy
4) Genetic Testing
5) Transfer of “unaffected” embryo
6) Advise against intercourse during IVF cycle
Polar Body Biopsy:
First (and/or Second) polar bodies are removed using ________ and _______
micromanipulator
microscope
Polar Body Biopsy:
Can only detect female chromosomal disorders because:
- 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
Polar Body Biopsy:
Samples extra-embryonic material because:
- Less likely to affect subsequent embryo development
- May be ethically preferable to some (when embryo screening is not permitted)
Blastomere Biopsy:
Goal is to remove one (or two) ____ cell(s) with minimal _____ to remaining embryo
Intact
trauma
Blastomere Biopsy:
Embryo is cultured in calcium and magnesium free medium because:
- Reduces blastomere-to-blastomere adherence
- Facilitates blastomere removal
Blastomere Biopsy:
Single blastomere is removed using micromanipulator and microscope because:
- Second blastomere may also be removed to confirm results from first blastomere
What is the goal of Trophectoderm Biopsy:
remove 5-10 cells with minimal trauma to reaming embryo
What is “FISH?”
Fluorescence in situ hybridization
What are some examples of “Current Technology?”
- Whole genome sequencing
- Single-gene testing
What does FISH accomplish?
- 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
FISH can only analyze about __chromosomes at most for a ____ cell, by this method
10; single
What 9 chromosomes does FISH detect?
X, Y, 13, 15, 16, 18, 21, 22
FISH is performed in ___ rounds on _____ nucleus
2; blastomere
What are 2 test that fall under current technology?
PGS and PGD
What is PGS and what does it accomplish?
Whole-genome sequencing
- Screens all 24 chromosomes simultaneously
- 22 autosomal and X and Y
- Detects aneuploidy
What is PGD and what does it accomplish?
Single-gene testing
- Detects single gene mutations
- Requires mutation analysis for both parents
Transfer of “unaffected” embryos:
Genetic/ Chromosome testing can be completed within ____/_____
24 hours; 1 week
Transfer of "unaffected" embryos: Blastomere biopsy ( from Day \_\_ embryo) may permit \_\_\_\_\_ of \_\_\_\_\_\_\_ (day \_\_ embryo)
03; transfer; blastocyst; 05
Transfer of “unaffected” embryos:
_____ biopsy requires _____ of blastocyst
Trophectoderm; freezing
What is mosaicism
- 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
During mosaicism, when does self-correction occur?
- Euploid cells proliferate faster than aneuploidy cells
- Mosaic embryos may halt proliferation of abnormal cells or exclude abnormal cells
