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Cytogenetic analysis of human blastocysts
Hazel J Clouston1, Mary Herbert, Jeanette Fenwick
1Department of Cytogenetics, Institute of Human Genetics, International Centre for Life, Newcastle upon Tyne, UK.
Prenatal Diagnosis
|November 28, 2002
Summary
Human blastocysts reveal the range of chromosome abnormalities, with most constitutional abnormalities established by this stage. This study analyzed 438 blastocysts to understand early embryonic aneuploidy.
Area of Science:
- Reproductive Biology
- Human Genetics
- Developmental Biology
Background:
- The human blastocyst is crucial for understanding constitutional chromosome abnormalities.
- Early embryonic development involves complex chromosomal processes.
Purpose of the Study:
- To determine the frequency and types of chromosome abnormalities in human blastocysts.
- To compare blastocyst chromosomal status with earlier embryonic stages and first-trimester pregnancies.
Main Methods:
- Utilized thymidine to synchronize cell division in IVF-generated blastocysts (5-8 days old).
- Employed G-band analysis after acetic acid disaggregation for metaphase preparation.
- Applied Fluorescence In Situ Hybridization (FISH) for detailed analysis of abnormalities and mosaicism.
Main Results:
- Analyzed 438 blastocysts; 3% were polyploid (primarily tetraploid), 29% were diploid/tetraploid mosaics, and 68% were uniformly diploid.
- Identified specific abnormalities including triploidy, trisomy 16, trisomy 2, and mosaic trisomies 3 and 7.
- Observed a range of chromosomal aberrations in the blastocyst stage.
Conclusions:
- Significant loss of certain aneuploidies (monosomies, some trisomies) occurs before the blastocyst stage.
- The blastocyst stage reflects the majority of constitutional chromosomal abnormalities seen in the first trimester.
- Chromosomal normality or abnormality is largely established by the blastocyst stage.