Sex selection

From Wikipedia, the free encyclopedia
This article is about the selection of the sex of offspring. For the evolutionary concept, see sexual selection.

Sex selection is the attempt to control the sex of the offspring to achieve a desired sex. It can be accomplished in several ways, both pre- and post-implantation of an embryo, as well as at birth. It has been marketed under the title family balancing.

Preference for sex of child

In many cultures, male offspring are desired in order to inherit property, carry on family name and to provide support for parents in old age.

In countries such as India, China and Nepal sons have been favored over daughters.[1][2][3][4][5] According to a 2011 Gallup poll, American parents favor boys by a 40% to 28% margin. The results were similar to a survey in 1941, when Americans preferred a boy to a girl by a 38% to 24% margin. The overall preference was driven by men, of whom 49% preferred a son compared to 22% who preferred a daughter. Men's preference for sons was most pronounced among men aged 18 to 29. Women, on the other hand, showed no preference for either sex, with 33% stating that they preferred a girl and 31% responding that they favored a boy.[6][7][8][9] Evidence suggests couples in the United Kingdom tend to pick sons and daughters in roughly even numbers.[10]

A 2009 study at the University of Ulster found that having sisters, as compared to brothers, can enhance the quality of an adult's life .[11]

Son Preference

There is a universal view that boys tend to have more privilege and freedom than girls do.[12] Nowhere is this more evident than the preference of parents to have a son over a daughter.[13] This can be observed through sex ratios of children in various countries.[14] Although biologically the sex ratio of children is around 95 girls to every 100 boys, this number generally evens out due to the higher infant mortality rate of boy infants.[15] However, in a number of countries, including China, Bangladesh, South Korea, India, and Pakistan, the sex ratio of children is severely distorted.[16] In these countries, the sex ratio is around 80 girls per 100 boys.[17] The preference for sons over daughters can be connected to a number of reasons. In these countries, it is argued that son preference is linked to factors including economics, religion, and culture.[18] Having a son ensures that families are more economically secure by not having to provide dowry payments, but rather being on the receiving end of this practice.[19] Furthermore, in countries where there are discriminatory practices regarding women inheriting, owing, or controlling land by law, having a son ensures that the family will not have to worry about the legal aftermath if something were to happen to them.[20] It can also be argued that parents in these countries are aware of the potential hardship their daughter would have to endure in her lifetime, and therefore prefer to have a son in order not to see their daughter endure such difficulties. Having a distorted sex ratio in which there are a higher percentage of boys in comparison to girls presents many consequences. Scholars have stated that this has lead to increased trafficking and kidnapping of women and girls.[21] It can be argued that crime rates, especially sexual crimes, have risen in these countries as a result.[22] Furthermore, this preference continues to empower men while devaluing women and prohibiting the view of women as equals throughout society.[23] By examining the higher ratio of men in countries that practice this preference, it is not without mentioning that the commonality of same-sex relationships could also rise since men are left without a suitable number of female partners. If this is the case, the acceptance of same-sex partnerships may increase, especially since the same countries that practice son preference are the very countries that do not support same-sex partnerships.[24] Lastly, it is important to recognize that although son preference is most common in the countries mentioned above, it is not necessarily the dominant view within these societies. As these countries, which are considered less developed than the West, continue to undergo transformation, negative views within cultural traditions are left within its history.

Methods

Pre-implantation

Two major types of pre-implantation methods can be used for social sex selection. Both of them are based on actively rendering the second sex chromosome to be either a Y chromosome (resulting in a male), or an X chromosome (resulting in a female).[25]

The Ericsson method

The Ericsson method, first applied in a clinical setting in the 1970s by Dr. Ronald J. Ericsson, uses higher concentrations of sperm of the desired sex to increase the likelihood of conceiving that sex. The method has a 70-72% success rate for boys and a 69-75% success rate for girls.[26] Currently, approximately 50 gender selection centers in the United States use the Ericsson Method for artificial gender selection.[27]

The Ericsson method separates male and female sperm by passing them through a column filled with blood protein, human serum albumin. As the sperm enter the human serum albumin, the differences in mass between the X and Y chromosomes manifest as the lighter male sperm push deeper into the protein than the females dragged down by the weight of the extra "leg" of the X sex chromosome.[28] This tiny difference creates separate layers of concentrated male and female sperm. The layers of gender-selected sperm are of higher concentrations but not pure. This lack of purity explains the 30% chance of gender selection failure of the Ericsson method.[29]

IVF/PGD technique

An 8-celled embryo prior to IVF/PGD analysis
Further information: IVF and Preimplantation genetic diagnosis

After ovarian stimulation, multiple eggs are removed from the mother. The eggs are fertilized in the laboratory using the father's sperm in a technique called in vitro fertilization (IVF). "In vitro" is Latin for "within glass". Fertilized eggs are called embryos. As the embryos develop through mitosis, they are separated by sex. Embryos of the desired gender are implanted back in the mother's uterus.

Prior to fertilization with IVF, the fertilized eggs can be genetically biopsied with preimplantation genetic diagnosis (PGD) to increase fertilization success.[30] Once an embryo grows to a 6-8 cell size, a small laser incision in the egg membrane (zona pellucida) allows safe removal of one of the cells.[31] Every cell in the embryo contains an identical copy of the genome of the entire person. Removal of one of these cells does not harm the developing embryo.[32] A Geneticist then studies the chromosomes in the extracted cells for genetic defects and for a definite analysis of the embryo’s gender.[33] Embryos of the desired sex and with acceptable genetics are then placed back into the mother. The IVF/PGD technique is favored over the Ericsson method because of the stricter control of the offspring gender in the laboratory. Since only embryos of the desired sex are transferred to the mother, IVF/PGD avoids the small likelihood present in the Ericsson method of an undesired sperm fertilizing the egg. Gender selection success rates for IVF/PGD are very high. The technique is recommended for couples who will not accept a child of the undesired gender.[34][35]

Timing methods

Timing methods aim to affect the sex ratio of the resultant children by having sexual intercourse at specific times as related to ovulation, but have shown no influence on the sex of the baby.[36]

  • The Shettles method, first formally theorized in the 1960s by Landrum B. Shettles, proposes that sperm containing the X (female) chromosome are more resilient than sperm containing the Y (male) chromosome. The method advocates intercourse two to four days prior to ovulation. By the time ovulation occurs, the cervix should contain a higher concentration of female sperm still capable of fertilization (with most of the male sperm already dead). Intercourse close to ovulation, on the other hand, should increase the chances of conceiving a boy since the concentration of Y sperm will be higher at the height of the menstrual cycle.[37]
  • The Whelan method is an "intercourse timing" method that advocates the opposite of the Shettles method. The Whelan method suggests intercourse four to six days prior to ovulation to increase likelihood of fertilization by male sperm.[38]

Sperm sorting

Main article: Sperm sorting

Sperm sorting is an advanced technique that sorts sperm "in vitro" by flow cytometry. This shines a laser at the sperm to distinguish X and Y chromosomes, and can automatically separate the sperm out into different samples. During the early to mid 1980s, Dr. Glenn Spaulding was the first to sort viable whole human and animal spermatozoa using a flow cytometer, and utilized the sorted motile rabbit sperm for artificial insemination. Subsequently, the first patent application disclosing the method to sort "two viable subpopulations enriched for x- or y- sperm" [39] was filed in April 1987 as US Application Serial Number 35,986 and later became part of US Patent 5,021,244; and the patent included the discovery of haploid expression (sex-associated membrane proteins, or SAM proteins) and the development of monoclonal antibodies to those proteins. Additional applications and methods were added, including antibodies, from 1987 through 1997.[40] At the time of the patent filing, both Lawrence Livermore National Laboratories and the USDA were only sorting fixed sperm nuclei,[41] after the Application Serial Number 35,986 patent filing a new technique was utilized by the USDA where "sperm were briefly sonicated to remove tails".[42] USDA in conjunction with Lawrence Livermore National Laboratories, 'Beltsfield Sperm Sexing Technology' relies on the DNA difference between the X- and Y- chromosomes.[43] Prior to flow cytometric sorting, semen is labeled with a fluorescent dye called Hoechst 33342 which binds to the DNA of each spermatozoon. As the X chromosome is larger (ie has more DNA) than the Y chromosome, the "female" (X-chromosome bearing) spermatozoa will absorb a greater amount of dye than its male (Y-chromosome bearing) counterpart. As a consequence, when exposed to UV light during flow cytometry, X spermatozoa fluoresce brighter than Y- spermatozoa. As the spermatozoa pass through the flow cytometer in single file, each spermatozoon is encased by a single droplet of fluid and assigned an electric charge corresponding to its chromosome status (eg X-positive charge, Y-negative charge). The stream of X- and Y- droplets is then separated by means of electrostatic deflection and collected into separate collection tubes for subsequent processing.[44] The technology is already in commercial use for animal farming.[45] It is currently being trialed on humans in the US under the trademark MicroSort; it claims a 90% success rate but is still considered experimental by the FDA.[46][47]

Post-implantation

Sex selection after implantation can be performed by prenatal sex discernment, followed by sex-selective abortion of any offspring of the unwanted sex. For prenatal sex discernment, a blood test can be taken from the mother for testing of small amounts of fetal DNA within it, and has been estimated to be reliable more than 98% of the time, as long as the samples are taken after the seventh week of pregnancy.[48][49]

Post-birth

Sex-selective infanticide - Killing children of the unwanted sex. Though illegal in most parts of the world, it is still practiced.

Sex-selective child abandonment - Abandoning children of the unwanted sex. Though illegal in most parts of the world, it is still practiced.

Sex-selective adoption - Placing children of the unwanted sex up for adoption. Less commonly viewed as a method of social sex selection, adoption affords families that have a gender preference a legal means of choosing offspring of a particular sex.

Ethical concerns

The application of these techniques to humans creates moral and ethical concerns in the opinion of some, while the advantages of sensible use of selected technologies is favored by others.

In contrast, in an interview study, sex-selection technology providers generally argued that sex selection is an expression of reproductive rights, was initiated and pursued by women, and was a sign of female empowerment that allowed couples to make well-informed family planning decisions, prevented occurrences of unintended pregnancy and abortion, and minimized intimate partner violence and/or child neglect.[50] In contrast, primary care physicians questioned whether women could truly express free choice under pressure from family and community.[50] In addition, primary care physicians voiced the concerns that sex selection led to invasive medical interventions in the absence of therapeutic indications, contributed to gender stereotypes that could result in child neglect of the lesser-desired sex, and was not a solution to domestic violence.[50]

Post-conceptual selection by preimplantation testing (PGD) also involves preferential use of embryos, and termination of pregnancy for gender selection also raises many ethical questions of the abortion debate.

Demographic concerns

In addition to the ethical concerns mentioned, issues of demographics arise in societies where social sex selection is common. A society may exhibit a widespread bias towards having children of a specific gender, either due to cultural biases or economic concerns (e.g. male children may be more employable in the future and thus provide more financial support). When combined with frequent social sex selection, this bias may produce a gender imbalance that has undesirable consequences. This phenomenon has been observed in many nations in the Far East, such as India and China, where social sex selection has produced unnaturally high male/female ratios in the population. China's gender imbalance is further increased by the One Child Policy, although applicable only in most urban populations. In these nations, a lack of opportunity for many men to marry is believed to be producing increases in crime, demand for prostitution, mass emigration, and the selling of brides.[51][52]

Major demographic changes have occurred in China because of sex selection. Chinese government reports show that the sex ratio for newborns is 118:100 (boys:girls), higher in rural areas such as Guangdong and Hainan (130:100) compared to the average of 104:100 in developed countries. It is believed that the ratio would increase further to the point that, by 2020, men of marriageable age would be unable to find mates, resulting in large social problems.[53][54]

Some nations, such as India, have attempted to curtail these gender imbalances with criminal statutes. In contrast, bioethicist Jacob Appel of New York University has argued that governments should pay couples to choose to have female children. According to Professor Appel, "if female babies [were] worth their weight in rupees and yuan, economic and educational opportunities for girls would soon follow."[citation needed]

In contrast, actual experience in Western cultures provides no evidence for any degree of gender imbalance from technologies which have long been available and legal - such as selective abortion or preimplantation embryo testing. When used for family balancing indications in such countries as the United States, pre-conceptual sex selection is widely sought without any preferential selection of males. Thus the right of individual families to determine whether or not to balance gender of offspring in their families is not and will not become, in many countries, a demographic issue. Furthermore, in countries where such demographic issues exist because of strong gender preferences in a segment of the population, regulatory and legal control of, without denial of access to, sperm sorting technology can be utilized to provide individuals with choices while ensuring that equal numbers of boys and girls are produced for population demographic equality.

Although problems such as rising crime rates may be associated with high male-female ratios (more males than females), it is not clear that such problems would arise in connection with low male-female ratios (fewer males than females). In addition, cultural practices such as polyamory and polyandry may reduce or eliminate potential problems. Also incentives for emigration of young singles out of gender imbalanced nations into more gender balanced nations, has often been seen as another solution to reduce potential social problems.[55]

History and folk beliefs

There are a wide variety of social sex selections methods which have not been demonstrated to be effective. Because even implausible and ineffective methods have a "success" rate of 50%, many continued to be recommended by word of mouth.

The Greeks and Romans did not have a consistent theory of how sex was determined. Pliny the Elder claims that tying the right testicle of a ram will cause him to produce only females, but does not claim this about other creatures.[56] Pseudo-Plutarch lists many Greek theories of sex determination, including heat and cold, left and right testicles, left and right sides of the body, sperm crossing or not crossing from one side of the womb to the other, and the strength or dominance of various body parts.[57]

Some people believe that timing conception according to astrological charts can influence a baby's sex,[58] though there is no evidence to support this or any other timing method. A 13th-century Chinese conception chart purports to be able to identify the sex of the baby before birth.

An 18th-century French book called The art of boys suggested an extreme method of ensuring children of one sex. The author suggests that one testicle and one ovary are intended for each sex. By removing a testicle or ovary, children of the other sex can be guaranteed.[59]

Sperm sorting utilizes the technique of flow cytometry to analyze and 'sort' spermatozoa. During the early to mid-1980s, Dr. Glenn Spaulding was the first to sort viable whole human and animal spermatozoa using a flow cytometer, and utilized the sorted motile rabbit sperm for artificial insemination. Subsequently, the first patent application disclosing the method to sort "two viable subpopulations enriched for x- or y- sperm"[39] was filed in April 1987 as US Application Serial Number 35,986 and later became part of US Patent 5,021,244; and the patent included the discovery of haploid expression (sex-associated membrane proteins, or SAM proteins) and the development of monoclonal antibodies to those proteins. Additional applications and methods were added, including antibodies, from 1987 through 1997.[40] At the time of the patent filing, both Lawrence Livermore National Laboratories and the USDA were only sorting fixed sperm nuclei,[60] after the Application Serial Number 35,986 patent filing a new technique was utilized by the USDA where "sperm were briefly sonicated to remove tails".[61] USDA in conjunction with Lawrence Livermore National Laboratories, 'Beltsfield Sperm Sexing Technology' relies on the DNA difference between the X- and Y- chromosomes.[62] Prior to flow cytometric sorting, semen is labeled with a fluorescent dye called Hoechst 33342 which binds to the DNA of each spermatozoon. As the X chromosome is larger (i.e. has more DNA) than the Y chromosome, the "female" (X-chromosome bearing) spermatozoa will absorb a greater amount of dye than its male (Y-chromosome bearing) counterpart. As a consequence, when exposed to UV light during flow cytometry, X spermatozoa fluoresce brighter than Y- spermatozoa. As the spermatozoa pass through the flow cytometer in single file, each spermatozoon is encased by a single droplet of fluid and assigned an electric charge corresponding to its chromosome status (e.g. X-positive charge, Y-negative charge). The stream of X- and Y- droplets is then separated by means of electrostatic deflection and collected into separate collection tubes for subsequent processing.[63]

Recently, a study published in 2006 indicated that mothers with toxoplasmosis have a significantly higher sex ratio of boys to girls. This has been discussed in connection with the manipulation hypothesis of parasites.[64] Another study found a link between sex and the diet of the mother, but this may be due to statistical chance, and has yet to be confirmed.[65]

Legality

Sex selection is officially prohibited in China, but the Chinese government admits that the practice is widespread, especially in rural areas of China and among lawless groups such as ghettoized migrant workers in cities (despite denials by the government-sponsored studies).[53][66]

Social sex selection is illegal in India. To ensure this, prenatal determination of sex through ultrasound is also illegal in India. These laws are instituted to combat the prevalent practice of sex-selective abortion. However, these laws have generally failed to be effective in rural areas and, despite education efforts, sex-selective abortion continues to be widely practiced there.

Sex selection is legal in most of the world, and it is practiced particularly in Western countries, but is more limited in Eastern countries, such as India or China. There is fertility tourism from the United Kingdom to the United States for sex selection, because preimplantation genetic diagnosis (PGD, a potential expansion of IVF), which can be used for sex selection, is prohibited in the UK, except when it is used to screen for genetic diseases, while the laws in the US are more relaxed in this subject.[10]

See also

References

  1. ↑ Ryju, S.; Lahiri-Dutt, eds. (2011). Doing gender, doing geography: emerging research in India. New Delhi: Routledge. p. 212. ISBN 978-0-415-59802-6. 
  2. ↑ Weiner, M.; Varshney, A.; Almond, G. A., eds. (2004). India and the politics of developing countries. Thousand Oaks, Calif.: SAGE Publications. p. 187. ISBN 978-0-7619-3287-1. 
  3. ↑ Joseph, W. A., ed. (2010). Politics in China: an introduction. Oxford: Oxford University Press. p. 308. ISBN 978-0-19-533530-9. 
  4. ↑ Lai-wan, C. C.; Eric, B.; Celia Hoi-Yan, Chan (2006). "Attitudes to and practices regarding sex selection in China". Prenatal Diagnosis 26 (7): 610–613. doi:10.1002/pd.1477. 
  5. ↑ "Sex selection: pervasiveness and preparedness in Nepal". United Nations Population Fund. September 2007. Retrieved May 13, 2013. 
  6. ↑ Rampell, C. (June 24, 2011). "Preferring Boys to Girls". The New York Times. Retrieved May 13, 2013. 
  7. ↑ "Gallup: Americans prefer having boys to girls, just as they did in 1941". CNN. June 13, 2011. Retrieved May 13, 2013. 
  8. ↑ Haas, M. (June 26, 2011). "Oh, Boy! The Anti-Girl Bias Is in Fashion". Huffington Post. Retrieved May 13, 2013. 
  9. ↑ Kim, C. (June 27, 2011). "Poll: More Americans Prefer Sons to Daughters". Time. Retrieved May 13, 2013. 
  10. ↑ 10.0 10.1 US clinic offers British couples the chance to choose the sex of their child From The Times. August 22, 2009
  11. ↑ Sisters 'make people happy'
  12. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  13. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  14. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  15. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  16. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  17. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  18. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  19. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  20. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 87. 
  21. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  22. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  23. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 42. 
  24. ↑ Seager, Joni (2009). The Penguin Atlas of Women in the World. New York, New York: Penguin Group. p. 27. 
  25. ↑ Dugdale, David, M.D. (February 19, 2009). "Chromosome url=http://www.nlm.nih.gov/medlineplus/ency/article/002327.htm". U.S. National Library of Medicine. 
  26. ↑ Beernink, FJ; Dmowski, WP; Ericsson, RJ (1993). "Sex preselection through albumin separation of sperm". Fertility and Sterility 59 (2): 382–6. PMID 8425635. 
  27. ↑ Silverman, M.D., Ph.D., Andrew Y. "Gender Selection Ericsson Method". Retrieved February 13, 2011. 
  28. ↑ Dmowski, WP; Gaynor, L; Rao, R; Lawrence, M; Scommegna, A (1979). "Use of albumin gradients for X and Y sperm separation and clinical experience with male sex preselection". Fertility and Sterility 31 (1): 52–7. PMID 283932. 
  29. ↑ Chen, M.; Guu, HF; Ho, ES (1997). "Efficiency of sex pre-selection of spermatozoa by albumin separation method evaluated by double-labelled fluorescence in-situ hybridization". Human Reproduction 12 (9): 1920–6. doi:10.1093/humrep/12.9.1920. PMID 9363707. 
  30. ↑ Pehlivan, T; Rubio, C; Rodrigo, L; Romero, J; Remohi, J; Simón, C; Pellicer, A (2003). "Impact of preimplantation genetic diagnosis on IVF outcome in implantation failure patients". Reproductive BioMedicine Online 6 (2): 232–7. doi:10.1016/S1472-6483(10)61715-4. PMID 12676006. 
  31. ↑ Boada, M.; Carrera, M.; De La Iglesia, C.; Sandalinas, M.; Barri, P. N.; Veiga, A. (1998). "Successful use of a laser for human embryo biopsy in preimplantation genetic diagnosis: report of two cases". Journal of Assisted Reproduction and Genetics 15 (5): 302–7. doi:10.1023/A:1022548612107. PMC 3454754. PMID 9604764. 
  32. ↑ Rice, Mary. "Children born after PGD as healthy as those born after conventional IVF treatment". European Society of Human Genetics. Retrieved February 12, 2011. 
  33. ↑ Bredenoord, Annelien; Dondorp, Wybo; Pennings, Guido; De Die-Smulders, Christine; Smeets, Bert; De Wert, Guido (2009). "Preimplantation genetic diagnosis for mitochondrial DNA disorders: ethical guidance for clinical practice". European Journal of Human Genetics 17 (12): 1550–9. doi:10.1038/ejhg.2009.88. PMC 2987024. PMID 19471315. 
  34. ↑ Kanavakis, E; Traeger-Synodinos, J (2002). "Preimplantation genetic diagnosis in clinical practice". Journal of Medical Genetics 39 (1): 6–11. doi:10.1136/jmg.39.1.6. PMC 1734958. PMID 11826017. 
  35. ↑ Silverman, M.D., Ph.D., Andrew Y. "Determine baby gender with IVF/PGD". Retrieved February 12, 2011. 
  36. ↑ Wilcox AJ, Weinberg CR, Baird DD (December 1995). "Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby". N. Engl. J. Med. 333 (23): 1517–21. doi:10.1056/NEJM199512073332301. PMID 7477165. 
  37. ↑ Gray, RH (1991). "Natural family planning and sex selection: fact or fiction?". American journal of obstetrics and gynecology 165 (6 Pt 2): 1982–4. doi:10.1016/S0002-9378(11)90558-4. PMID 1836712. 
  38. ↑ Shettles, L.; D.M. Rorvick (2006). "How Do They Compare?". In Martin J. Whittle and C. H. Rodeck. How to Choose the Sex of Your Baby: The Method Best Supported by Scientific Evidence. New York: Random House. p. . ISBN 978-0-7679-2610-2. 
  39. ↑ 39.0 39.1 US Patent 5,021,244, column 9, Sorting Sperm; http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5021244.PN.&OS=PN/5021244&RS=PN/5021244
  40. ↑ 40.0 40.1 US Patent 5,021,244; 5,346,990; 5,369,012; 5,439,362; 5,496,722; 5,648,468; 5,660,997; PCT/US1989/002069
  41. ↑ L. A. Johnson, J. P. Flook, M. V. Look, D. Pinkel, Flow sorting of X and Y chromosome-bearing spermatozoa into two populations. Gamete Research Volume 16, Issue1, pages 1-9, January 1987; http://onlinelibrary.wiley.com/doi/10.1002/mrd.1120160102/abstract
  42. ↑ L. A. Johnson, J. P. Flook and M. V. Look, Flow cytometry of X and Y chromosome-bearing sperm for DNA using an improved preparation method and staining with Hoechst 33342. Gamete Research Volume 17, Issue 3, July 1987, Pages: 203–212; http://onlinelibrary.wiley.com/doi/10.1002/mrd.1120170303/abstract
  43. ↑ Garner DL, Seidel GE. History of commercializing sexed semen for cattle. Theriogenology 2008;69: 886-895.
  44. ↑ Seidel GE, Jr., Garner DL. Current status of sexing mammalian spermatozoa. Reproduction 2002;124: 733-743.
  45. ↑ ABC Landline, Dairy farms use gender selection process, 2006.
  46. ↑ "MicroSort Information". MicroSort, Inc. Retrieved February 13, 2011. 
  47. ↑ Mayor S (July 2001). "Specialists question effectiveness of sex selection technique". BMJ 323 (7304): 67. doi:10.1136/bmj.323.7304.67. PMC 1120747. PMID 11451774. 
  48. ↑ Devaney SA, Palomaki GE, Scott JA, Bianchi DW (2011). "Noninvasive Fetal Sex Determination Using Cell-Free Fetal DNA". JAMA 306 (6): 627–636. doi:10.1001/jama.2011.1114. PMID 21828326. 
  49. ↑ Roberts, Michelle (10 August 2011). "Baby gender blood tests 'accurate'". BBC News Online. 
  50. ↑ 50.0 50.1 50.2 Puri S, Nachtigall RD (May 2010). "The ethics of sex selection: a comparison of the attitudes and experiences of primary care physicians and physician providers of clinical sex selection services". Fertil. Steril. 93 (7): 2107–14. doi:10.1016/j.fertnstert.2009.02.053. PMID 19342036. 
  51. ↑ India's lost girls, BBC Online, 4 Feb 2003.
  52. ↑ China facing major gender imbalance, MSNBC, 12 Jan 2007.Archive
  53. ↑ 53.0 53.1 China facing major gender imbalance - Asia-Pacific - msnbc.com
  54. ↑ "China fears bachelor future". BBC News. April 5, 2004. 
  55. ↑ "Infanticide, Abortion Responsible for 60 Million Girls Missing in Asia". Fox News. June 13, 2007. 
  56. ↑ Pliny the Elder, The Natural History, Book XXX, Chapter 16.
  57. ↑ Pseudo-Plutarch, Placita Philosophorum, Book V, Chapter VII.
  58. ↑ Ancient chinese birth gender chart
  59. ↑ Michel Procope-Couteaux, L'art de faire des garçons, 1770, p. 129.
  60. ↑ Johnson LA, Flook JP, Look MV, Pinkel D (January 1987). "Flow sorting of X and Y chromosome-bearing spermatozoa into two populations". Gamete Res 16 (1): 1–9. doi:10.1002/mrd.1120160102. PMID 3506896. 
  61. ↑ Johnson LA, Flook JP, Look MV (July 1987). "Flow cytometry of X and Y chromosome-bearing sperm for DNA using an improved preparation method and staining with Hoechst 33342". Gamete Res 17 (3): 203–12. doi:10.1002/mrd.1120170303. PMID 3507347. 
  62. ↑ Garner DL, Seidel GE (April 2008). "History of commercializing sexed semen for cattle". Theriogenology 69 (7): 886–95. doi:10.1016/j.theriogenology.2008.01.006. PMID 18343491. 
  63. ↑ Seidel GE, Garner DL (December 2002). "Current status of sexing mammalian spermatozoa". Reproduction 124 (6): 733–43. doi:10.1530/rep.0.1240733. PMID 12537000. 
  64. ↑ Flegr, Jaroslav; Sulc, J; Nouzová, K; Fajfrlík, K; Frynta, D; Flegr, J (2007). "Women infected with parasite Toxoplasma have more sons" (PDF). Naturwissenschaften 94 (2): 122–7. doi:10.1007/s00114-006-0166-2. PMID 17028886. 
  65. ↑ Can A Pregnant Woman's Diet Affect Baby's Sex?
  66. ↑ Gender imbalance in China October 27, 2008 - Shorenstein APARC, AHPP, SCP News. By Shannon Davidson, Jennifer Bunnell and Fei Yan

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