embryo biopsy definition of embryo biopsy in the Free Online Encyclopedia.

embryo biopsy or preimplantation genetic diagnosis (PGD), diagnostic procedure, used in genetic screening genetic screening, testing for genetic disorders. Most commonly, prospective parents or an embryo or fetus is tested when a specific genetic disorder is suspected (e.g., Tay-Sachs or sickle cell disease ).
..... Click the link for more information. , in which a single cell is removed from an embryo two or three days after it has been conceived through in vitro fertilization in vitro fertilization (vē`trō, vĭ`trō), technique for conception of a human embryo outside the mother's body.
..... Click the link for more information. . At this age the embryo consists of about eight genetically identical cells. The embryo itself is unaffected and continues to grow while the selected cell's genes are replicated using polymerase chain reaction polymerase chain reaction (pŏl`ĭmərās')
..... Click the link for more information. and then studied for genetic defects. The procedure allows an embryo to be tested before it is implanted into the womb when an inheritable disease or a genetic predisposition to a disease is carried by or exhibited in one or both parents.

Embryo biopsy has been used successfully to screen for such diseases as cystic fibrosis cystic fibrosis (sĭs`tĭk fībrō`sĭs)
..... Click the link for more information. and Tay-Sachs Tay-Sachs disease (tā`-săks`)
..... Click the link for more information. as well as for genes that predispose a person to breast or colon cancer. The procedure can also be used to determine the gender of the embryo. Given this ability, X-chromosome-linked diseases that manifest only in males (hemophilia hemophilia (hē'məfĭl`ēə,–fēl`yə)
..... Click the link for more information. , for example) can be "screened" by implanting only female embryos (which will carry but will not develop the disease). Another variation, used for women over 35 (women past that age being statistically more likely to give birth to babies with Down syndrome Down syndrome, congenital disorder characterized by mild to severe mental retardation , slow physical development, and characteristic physical features. Down syndrome affects about 1 in every 730 live births and occurs in all populations equally.
..... Click the link for more information. and other chromosomal defects) involves examining the sample to make sure it has the correct number of chromosomes. Embryo biopsy has also been used to select a child who is a compatible donor for a sibling with a life-threatening disease such as certain anemias and leukemias.

See also amniocentesis amniocentesis (ăm'nēō'sĕntē`sĭs)
..... Click the link for more information. ; birth defects birth defects, abnormalities in physical or mental structure or function that are present at birth. They range from minor to seriously deforming or life-threatening. A major defect of some type occurs in approximately 3% of all births.
..... Click the link for more information. ; chorionic villus sampling chorionic villus sampling (CVS) or chorionic villus biopsy (CVB) (kōr'ē-ŏn`ĭk, kôr'–)
..... Click the link for more information. .