Reproductive Biology Associates
Preimplantation Genetic Diagnosis (PGD) and Embryo Biopsy
Each of the 100 trillion cells in the human body (except for red blood cells) contains the entire human genome. Chromosomes are the string-like elements within the nucleus (center) of every cell of your body. They contain genetic information made of DNA. A gene occupies a specific location on a chromosome. Normally, there are 23 identical pairs of chromosomes (6 feet of DNA) in each cell, with a total of 46 chromosomes. Each partner normally provides 23 chromosomes during fertilization. If an egg or sperm have an abnormal chromosome package, the embryo that they create will have a chromosomal abnormality as well. This is sometimes due to a rearrangement of chromosomes, or a missing piece of a chromosome. In some cases there is a missing chromosome, or an extra chromosome (aneuploidy) leading to an inheritable disorder. Any embryo with a missing chromosome (monosomy) will stop growing before implantation (fatal anomaly). If the aneuploidy involves chromosomes including 13, 18, 21, X or Y, the pregnancy may go to term. The most common of these non-fatal anomalies is trisomy 21, or Downs syndrome, in which an extra chromosome 21 is present. Others include Turner’s syndrome in females and Klinefelter’s Syndrome in males.