Question

Preimplantation genetic diagnosis and its types.

Hint:

PGD helps prevent the transmission of genetic disorders by selecting embryos free of specific genetic conditions, but it comes with ethical and social implications.

Answer 1

Preimplantation genetic diagnosis (PGD) is a technique used to detect genetic defects in embryos before implantation during an in vitro fertilization (IVF) cycle. PGD allows for the selection of embryos without specific genetic conditions, ensuring healthier pregnancies.
Step 1: Process of PGD:
1. Embryo Biopsy: In PGD, a single cell is removed from an embryo at the 6-8 cell stage (usually on day 3 of development). The DNA from this cell is then analyzed for genetic defects.
2. Genetic Testing: The biopsy cells are tested for specific genetic disorders, chromosomal abnormalities, or inherited mutations using techniques like PCR (Polymerase Chain Reaction) or FISH (Fluorescence In Situ Hybridization).
Step 2: Types of Preimplantation Genetic Diagnosis:
1. PGD for Single Gene Disorders: This involves testing embryos for single gene disorders, such as cystic fibrosis, sickle cell anemia, or Huntington’s disease. This type of PGD is performed when one or both parents are carriers of a known genetic condition.
2. PGD for Chromosomal Disorders: This is used to detect chromosomal abnormalities such as Down syndrome (trisomy 21) or other chromosomal rearrangements. This type of PGD is typically recommended for older women or those with a history of recurrent miscarriage.
3. PGD for HLA Typing: In this case, embryos are tested to identify whether they can be a potential match for a sibling needing stem cell or bone marrow transplant. This is done for cases where a child needs a stem cell donor, such as in certain blood cancers.
Step 3: Ethical Considerations:
While PGD offers significant benefits, there are ethical concerns about embryo selection, especially when used for non-medical purposes like gender selection. Additionally, the potential for the rejection of certain embryos can raise emotional and moral dilemmas for parents.