Tuesday, August 3, 2010



Sexual selection is a term which refers to a medical technique used for selecting the gender (sex) of an offspring. This is achieved through a series of processes that begins with in vitro fertilization (IVF), a process where the egg cell (ova) if removed from the female’s ovary and fertilised by sperm, in a fluid medium, outside the womb and then implanted into the female’s uterus (to induce a pregnancy). For sexual selection, the sperm which fertilise the ova is also from a range of selected samples (by separation), and subsequently the embryos are selected for transfer and implantation. Selective termination of pregnancy is done and the whole process repeated until a desired result is obtained, i.e. the desired gender of offspring is conceived.

Prenatal screening, also called prenatal diagnosis, on the other hand, are a series of tests carried out on pregnant women in order to check the health status of a developing baby. These tests are done during early pregnancy (usually within the first 20 weeks) and they are also a means of sex determination, where the sex of the developing baby is seen. Though a screening test does not tell for sure if a developing baby has a certain problem, it does however give an idea on the likelihood of its occurrence.

Some of the tests include maternal serum screen (MSS) where the blood sample from the mother is used to check the health of the developing baby. The blood in the mother arm contains some substances that are present in all pregnant women, and out-of-range levels of those substances usually indicate either Down syndrome or spina bifida. Ultrasound is a method of sonic photography where sound waves are used to project the picture of a foetus on a special screen. It is the method used for sex determination. Another test is through simple questionnaire and enquiry about history of genetic diseases and a special kind of ultrasound is also used for further diagnosis of spina bifida.
Sexual selection for prenatal screening is the coupling of both processes in order to conceive and deliver a health offspring of a pre-determined gender.

Obtaining Fetal DNA
First DNA is obtained from the unborn child for testing. The oldest procedure for doing this is amniocentesis, which is usually performed between 15 and 18 weeks of pregnancy. Ultrasound is used to guide a long, hollow needle through the woman's abdominal wall and into the amniotic fluid surrounding the fetus. A small amount of amniotic fluid that contains some cells sloughed off from the fetus is then removed via the needle and cultured for one to two weeks before the cells are ready to be used in genetic testing.

Another method, alternative to amniocetesis, called Chorionic villus sampling (CVS) can be employed. It is slightly more risky and is performed earlier in the course of development, between 10 and 12 weeks of pregnancy. Because the placenta is derived from the extra embryonic portion of the early embryo, the villus cells in the placenta have the same genetic composition as the cells in the fetus's tissues, but they can be removed without harming the fetus.
Some techniques can be used which are not as invasive as the above mentioned techniques.

Testing for Abnormalities in Fetal DNA

After isolating of fetal DNA, it can be tested for a variety of genetic abnormalities, including the most common maternal-fetal incompatibilities for the rhesus D antigen, as well as other more ethically controversial factors, like the child's sex. The presence of additional chromosomes or chromosome translocations in a karyotype  may be indicating factors of Down syndrome. Healthy individuals may also be unwitting carriers of chromosomal translocation that can be passed down to their children. Translocation carriers have the full complement of genes, but one or more of their chromosomes are abnormal, depending on whether the translocation resulted from chromosome fusion or from a reciprocal exchange between two chromosomes. Carriers of translocations display a range of reproductive problems. Moreover, they sometimes have other children who died in infancy or who have mental retardation, because most of the gametes produced by translocation carriers are aneuploid. Today, the use of genetic testing techniques makes it possible to determine whether a fetus is a healthy translocation carrier.
The availability of a genetic profile for a developing fetus is an important family planning tool. Its only shortcoming is that by the time these tests can be performed, the pregnancy is already well under way, so the parents often face profound ethical dilemmas regarding family planning. An alternative in vitro testing method called pre-implantation genetic diagnosis (PGD) does exist, but it carries with it a whole new set of ethical issues.
PGD depends on methods that are routinely used for in vitro fertilization (IVF). Multiple oocytes are first collected from the ovaries of a prospective mother who has been treated with hormones that cause her to "super ovulate," and these oocytes are then fertilized using the father's sperm. Successful fertilizations can be detected by the fusion of the maternal and

-Counselling before a test is done, helps the woman decide which test, if any, and is best for the woman and the baby
- Prenatal Screen detects foetal abnormalities: tests that may identify a baby as being at an increased risk of having a particular problem.
-The process enables couple to have the desired gender of a child.
-It is useful where there is an unbalance of gender, if more males than females then females can be “created” and vice versa.
- No one wants to pass on a debilitating physical condition to the next generation, but all pregnancies carry some degree of risk

- These testes can cause the mother to have a miscarriage or develop an infection
-No test gives a 100% guarantee of a healthy baby. The tests give some information about the baby’s health. They do not necessarily find all potential health problems.
-Testing procedure during amniocentesis carries with it a high risk of infection and possible miscarriages.




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