Читать книгу Lifespan Development - Tara L. Kuther - Страница 107

Sperm cells can be sorted by whether they carry the X or Y chromosome. Through in vitro fertlization a zygote with the desired sex is created.

Brain light / Alamy Stock Photo

Parents have long shown a preference for giving birth to a girl or boy, depending on circumstances such as cultural or religious traditions, the availability of males or females to perform certain kinds of work important to the family or society, or the sex of the couple’s other children. Yet, throughout human history until recently, the sex of an unborn child was a matter of hope, prayer, and folk rituals. It is only in the past generation that science has made it possible for parents to reliably choose the sex of their unborn child. The introduction of sex selection has been a boon to couples carrying a genetically transmitted disease (i.e., a disease carried on the sex chromosomes), enabling them to have a healthy baby of the sex unaffected by the disease they carried.

There are two methods of sex selection: preconception sperm sorting and preimplantation genetic diagnosis (PGD) (Bhatia, 2018). Preconception sperm sorting involves staining the sperm with a fluorescent dye and then leading them past a laser beam where the difference in DNA content between X- and Y-bearing sperm is visible. PGD creates zygotes within the laboratory by removing eggs from the woman and fertilizing them with sperm. This is known as in vitro (literally, “in glass”) fertilization because fertilization takes place in a test tube, outside of the woman’s body. After 3 days, a cell from each blastula is extracted to examine the chromosomes and determine whether or not it contains a Y chromosome (i.e., whether it is female or male). The desired male or female embryos are then implanted into the woman’s uterus. The second type of sex selection, sperm sorting, entails spinning sperm in a centrifuge to separate those that carry an X or a Y chromosome. Sperm with the desired chromosomes are then used to fertilize the ovum either vaginally or through in vitro fertilization.

As sex selection becomes more widely available, parents may seek to choose the sex of their child because of personal desires, such as to create family balance or to conform to cultural valuing of one sex over the other, rather than to avoid transmitting genetic disorders (Robertson & Hickman, 2013). Critics argue that sex selection can lead down a “slippery slope” of selecting for other characteristics—hair color, eye color, intelligence, and more (Dondorp et al., 2013). Might children born from gender selection be expected to act in certain sex-typical ways, and if they do not, might that disappoint parents? Others express concerns about societal sex ratio imbalances if sex selection becomes widely practiced (Colls et al., 2009; Robertson & Hickman, 2013). Such sex ratio imbalances favoring males have occurred in India and China because of female infanticide, gender-driven abortion, and China’s one-child family policy (see the Cultural Influences on Development feature in Chapter 10 for more information; Bhatia, 2010; Ethics Committee of the American Society for Reproductive Medicine, 2001).

Should selecting an embryo’s sex be a matter of parental choice? A review of 36 countries, including 25 in Europe, revealed that many had no policies regarding selection; those that did prohibited sex selection for nonmedical reasons (Darnovsky, 2009). The European Union bans socially, nontherapeutically motivated sex selection (Council of Europe, 1997). The United States does not have a formal policy regarding sex selection (Deeney, 2013). Sex selection remains hotly debated in medical journals, hospital and university ethics boards, and the public.