Friday 15 July 2016

Sex Selection in Humans



Throughout history, people have attempted to influence the gender of their unborn offspring by following varied and sometimes bizarre procedures. In medieval Europe, prospective parents would place a hammer under the bed to help them conceive a boy, or a pair of scissors to conceive a girl. Other practices were based on the ancient belief that semen from the right testicle created male offspring and that from the left testicle created females. As late as the eighteenth century, European men might tie off or remove their left testicle to increase the chances of getting a male heir.

In some cultures, efforts to control the sex of offspring has had a darker outcome— female infanticide. In ancient Greece, the murder of female infants was so common that the male:female ratio in some areas approached 4:1. In some parts of rural India, hundreds of families admitted to female infanticide as late as the 1990s. In 1997, the World Health Organisation reported population data showing that about 50 million women were “missing” in China, likely because of selective abortion of female fetuses and institutionalized neglect of female children.

In recent times, sex-specific abortion has replaced much of the traditional female infanticide. For a fee, some companies offer amniocentesis and ultrasound tests for prenatal sex determination. Studies in India estimate that hundreds of thousands of fetuses are aborted each year because they are female. As a result of sex-selective abortion, the female:male ratio in India was 927:1000 in 1991. In some northern states, the ratio was as low as 600:1000.

In Western industrial countries, new genetics and reproductive technologies offer parents ways to select their children’s gender prior to implantation of the embryo in the uterus—called preimplantation gender selection (PGS). Following in vitro fertilization, embryos are biopsied and assessed for gender. Only sex- selected embryos are then implanted. The simplest method involves separating X and Y chromosome-bearing spermatozoa based on their DNA content. Because of the difference in size of the X and Y chromosomes, X-bearing sperm contain 2.8 to 3.0 percent more DNA than Y-bearing sperm. Sperm samples are treated with a fluorescent DNA stain, then passed through a laser beam in a Fluorescence-Activated Cell Sorter (FACS) machine that separates the sperm into two fractions based on the intensity of their DNA-fluorescence. The sorted sperm are then used for standard intrauterine insemination.


The emerging PGS methods raise a number of legal and ethical issues. Some people feel that prospective parents have the legal right to use sex-selection techniques as part of their fundamental procreative liberty. Proponents state that PGS will reduce the suffering of many families. For example, people at risk for transmitting X-linked diseases such as hemophilia or Duchenne muscular dystrophy can now enhance their chance of conceiving a female child, who will not express the disease.

The majority of people who undertake PGS, however, do so for nonmedical reasons—to “balance” their families. A possible argument in favor of this use is that the ability to intentionally select the sex of an offspring may reduce overpopulation and economic burdens for families who would repeatedly reproduce to get the desired gender. By the same token, PGS may reduce the number of abortions. It is also possible that PGS may increase the happiness of both parents and children, as the children would be more “wanted.”



On the other hand, some argue that PGS serves neither the individual nor the common good. They argue that PGS is inherently sexist, having its basis in the idea that one sex is superior to the other, and leads to an increase in linking a child’s worth to gender. Other critics fear that social approval of PGS will open the door to other genetic manipulations of children’s characteristics. It is difficult to predict the full effects that PGS will bring to the world. But the gender-selection genie is now out of the bottle and is unwilling to return.

Investigate the references and links below to help you understand some of the issues that surround the topic of gender selection. Answer the following questions:

1. What do you think are valid arguments for and against the use of PGS?
2. A generally accepted moral and legal concept is that of reproductive autonomy—the freedom to make individual reproductive decisions without external interference. Are there circumstances under which reproductive autonomy should be restricted?
3. What do you think are the reasons that some societies practice female infanticide and prefer the birth of male children?
4. If safe and efficient methods of PGS were available to you, do you think that you would use them to help you with family planning? Under what circumstances might you use them?

References for further reading:
The above questions, and others, are explored in a series of articles in the American Journal of Bioethics, Volume 1 (2001). See the article by J. A. Robertson on pages 2–9, for a summary of the moral and legal issues surrounding PGS.
“ Gendercide Watch” Web site http://www.gendercide.org/

The Genetics and IVF Institute (Fairfax, Virginia) is presently using PGS techniques based on sperm sorting, in an FDA-approved clinical trial. As of 2008, over 1000 human pregnancies have resulted, with an approximately 80 percent success rate. Read about these methods on their Web site: http://www.microsort.com/
                                            Adopted from: Concepts of Genetics 11th edition by Klug, Cummings, Spencer, Palladino p.193



Girls Changing to Boys: The Case of the Guevedoces



In humans sex is determined by the X and Y chromosomes: Female XX and male XY. In a remote community in the Dominican Republic a it was discovered that some children were born looking like girls, with no testes and what appears to be a vagina. Once these children reach puberty then the penis grows and testicles descend. These children have been called "Guevedoces" which literally means "penis at 12".

It was discovered that Guevedoces children have a deficiency of the 5-alpha-reductase which is an enzyme that converts testosterone to dihydrotestosterone (DHT), a more potent androgen. This deficiency is a genetic condition resulting from a mutation in the 5-alpha-reductase 2 gene located on chromosome 2. DHT and testosterone are essential for the normal development of the male sex characteristics. DHT directs the development of the external male genitalia before birth, thus its absence results in an XY child being born with ambiguous genetalia and often mistaken for a girl. However, at puberty the individual will receive a second dose of testosterone which will promote the growth of the penis.




Read the stories of some of these children
Extraordinary case of the Guevedoces
Guevedoces: Rare medical condition
Curious case of the children whose penises don't appear until puberty

Friday 6 May 2016

The Age of Genetics




Genetically Modified Foods




The "Age of Genetics" was created by remarkable advances in the use of biotechnology to manipulate plant and animal genomes. Given that the world population has topped 6 billion and is expected to reach 9.2 billion by 2050, some scientists have proposed that only the worldwide introduction of genetically modified (GM) foods will increase crop yields enough to meet future nutritional demands. Pest resistance, herbicide, cold, drought, and salinity tolerance, along with increased nutrition, are seen as positive attributes of GM foods. However, others caution that unintended harm to other organisms, reduced effectiveness to pesticides, gene transfer to non-target species, allergenicity, and as yet unknown effects on human health are potential concerns regarding GM foods.

If you were in a position to control the introduction of a GM primary food product (rice, for example), what criteria would you establish before allowing such introduction?
Write your answers in the comments section.
(Adopted from Concepts of Genetics 10th Edition, Klug, Cummings, Spencer, Palladino)