Monday, 19 March 2012

Designer Babies – Preimplantation Genetic Diagnosis


Inheriting genes of unfavourable nature has plagued humanity since the dawn of time. And it was long before Gregor Mendel’s discovery of how our physical and behavioural traits are inherited, that humans had already established a desire for the customization of our off springs characterized by disease-free-inheritance matched by superior physical and behavioural genes such as good looks, intelligence and athleticism. [4] It was not until the beginning of the 21st century that scientists started making advances in this sensitive area of eugenics, colloquially termed designer baby – “a baby whose genetic make-up has been modified in order to eradicate a particular defect, or to ensure that a particular gene is present.”  [1] In spite of the ethical concerns, scientists continue to put preimplantation genetic diagnosis (PGD) into practice, involving in vitro fertilization (IVF) to examine chromosomal abnormalities and perform procedures on the embryo’s DNA before implantation. [2]

FIGURE 1: Embryo cells being removed

The biological causes of genetic variation is at the heart of what PGD aims to eliminate. The three most common mechanisms that arise from sexual reproduction are independent assortment of chromosomes, crossing over and random fertilization. Mendel’s Law of Independent Assortment tells us that during meiosis each pair of alleles segregates independently of each other pair of alleles. [3] And thus, each sperm cell carries chromosomes with a unique combination of the male’s genes and it is by chance that any one of the sperm cells will fertilize the female’s egg – the random nature of fertilization. Finally, the crossing over of alleles results in recombinant chromosomes the uniquely combined DNA from both parents. A fourth less common mechanism, Mutations can also develop whereby DNA replication encompasses an error either during meiosis or mitosis in a zygote.  [3] How can PGD reverse this variance at a cellular level?

PGD was originally developed to eradicate life-threatening diseases in unborn babies and to instill a sense of security in the mother, yet in more recent times it has gone one step further to enhance superficial features. PGD, first of all involves the fusion of gametes in the lab. Mitotic divisions form a cluster of embryo cells.  An incision is made through the membrane using acid and cells are removed. Each cell undergoes genetic analysis biopsy using Fluorescent in-situ Hybridization (FISH). Chemicals are used to illuminate chromosomes to correspond to a particular colour. A DNA probe is used to visualize the cell for genetic analysis. This process is repeated until a cell of favourable genes is found, which is implanted into the mother’s womb. All other cells are discarded, which brings up ethical concerns.



Figure 3: Unnatural Selection using PGD                                                             

Perhaps the practicality of PGD can be improved by maximizing its benefits while minimizing harm. Chromosomal analysis is quite often essential in couples, who carry balanced translocations, in advanced age women and women with previous children who have abnormal chromosome numbers. In addition, women experiencing recurrent pregnancy loss, recurring poor quality embryos or repeated IVF failures could also benefit from the PGD procedure to select healthy embryos. PGD can be arguably unethical due to its superficial and selective nature but its benefits looms large for those in need. [6]
 

References

1.     Definition for designer baby - Oxford Dictionaries Online (World English)." Oxford Dictionaries Online. N.p., n.d. Web. 14 Mar. 2012. .
2.     Genetic Testing PGD | Fertility Treatment | IVFAustralia." IVFAustralia. N.p., n.d. Web. 14 Mar. 2012. .
3.     Reece, Jane B., and Neil A. Campbell. Campbell biology Jane B. Reece et al. 9th ed. Boston: Benjamin Cummings :, 2011. Print.
4.     BBC - Science & Nature - Horizon - Designer Babies." BBC - Homepage. N.p., n.d. Web. 15 Mar. 2012.
5.     FISH in PGD." IVF Fertility Clinic | Chicago Infertility Specialist - Dr. Randy Morris. N.p., n.d. Web. 19 Mar. 2012. .
6.     Preimplantation genetic diagnosis, PGD, PGD by FISH, Common chromosomal abnormalities, FISH, aneuploidy, IVF cycle, Blastomere biopsy, genetic disorders, embryo biopsy, FISH for anruploidies, Chromosomal aneuploidies, Couples with balanced translocations, Women with advanced age, Recurrent pregnancy loss, IVF failures, Selecting normal embryo, blastomere, preimplantation embryos, Klinefelter Syndrome." New Document . N.p., n.d. Web. 19 Mar. 2012.


2 comments:

  1. Preimplantation genetic diagnosis, or PGD as it is known for short, is used for the identification of genetic defects in embryos that are created using in vitro fertilization or other forms of assisted reproductive technologies. The procedure may also be used for gender selection purposes as well.

    PGD Preimplantation Genetic Diagnosis

    ReplyDelete
  2. PGD may be used if one or both of the parents have a known genetic abnormality, as the embryos are put through a panel of tests looking for various common chromosome abnormalities.

    PGD

    ReplyDelete