Reproduction Research Assignment Sac 5 PART 1 : Asexual vs. Sexual Reproduction [ 4 marks ] – Discuss the differences between, and the advantages and disadvantages of sexual and asexual reproduction : SEXUAL REPRODUCTION Sexual Reproduction is the formation of a new organism from two parents usually, and involves the joining of gametes [ e. g. sperm, pollen, egg] to form a single cell called a zygote [ or fertilised egg ]. The offspring are similar, but not identical to the parents. Sexually Reproductive organisms include mammals, most reptiles, and flowering plants. ADVANTAGES
There is greater genetic variation of the offspring and therefore, greater chance of survival in changing environments. Asexual Reproduction is the process by which a single organism produces a new organism identical to itself. An asexually reproducing organism does not require a partner to produce offspring. It is a process that requires no fusion of gametes whatsoever. Asexually Reproductive organisms include bacteria, nonflowering plants and some reptiles. DISADVANTAGES Some disadvantages of sexual reproduction are the facts that it requires 2 parents, so if one species dies out, they can no longer reproduce.
Sexual reproduction also poses risks of mutations and hereditary diseases. Sexual reproduction is also not as rapid as asexual reproduction. Energy is also expended in finding a mate in many organisms. However some organisms have both male and female reproductive organs that are able to produce gametes simultaneously. ASEXUAL REPRODUCTION Asexual reproduction is the formation of a new organism when there is the presence of a single parent and no joining gametes [ e. g. sperm, pollen, egg ]. The offspring has identical genes and chromosomes to the parent. ADVANTAGES No energy is expended in finding a mate. here is a high chance of survival of the offspring, if the offspring remains near the parent in a stable environment. DISADVANTAGES Less genetic diversity gives the offspring a lesser chance of survival if the environment changes. – Discuss the relevance of mitosis and meiosis to sexual and asexual reproduction ; Mitosis is the asexual form of reproduction, Meiosis being the sexual form. Mitosis involved replicating the Chromosomes of the cell and placing the exact replicas in the daughter cells, resulting in 2 cells. This is asexual reproduction because the cells are exactly the same.
Meiosis involved replication of the chromosomes, random mixing of them and division into 2 cells, duplication and random mixing again and then division into two more cells resulting in 4 cells. This is sexual reproduction because the cells are not exactly the same. – Include examples of the different types of asexual reproduction ; 1. Binary Fission [ Bacteria and Amoeba ] occurs when a cell simply grows larger, replicates its DNA in genes and chromosomes, and then forms a cell membrane down the midsection of the cell to form two new “ daughter” cells. 2.
Budding [ Of Yeast and Hydras ] occurs when a small part of the parent’s body separates from the rest of the rest and develops into a new individual, eventually either becoming an independent organism or part of an attached colony. 3. Spore Formation [ e. g. of Ferns, Malaria – Causing Protozoan called Plasmodium ] occurs where special cells with resistant coverings form. These coverings are resistant to unfavourable environmental conditions such as heat or dryness. 4. Fragmentation [ e. g. of Flatworms and Starfish ] occurs when a parent body is broken into pieces and each piece may form a new individual. . Regeneration [ Of Many Plants ] occurs when part of an organism grows to form other organisms that are often still connected to the original organism. Examples of regeneration in plants are the vegetative propagation of runners, of grasses, strawberries, rhizomes in ferns, tubers in potatoes and growing plants from cuttings. 6. Parthenogenesis [ e. g. Bees, Wasps, some Cockroaches and Liver Flukes inside a host ] occurs when a new organism develops from an unfertilised egg. For example, in honeybees, the female or queen is inseminated only once in her lifetime.
The sperm she receives is stored in a little pouch connected to the genital tract and closed off by a muscular valve. Whether or not she chooses to release the sperm to fertilise her eggs, and create female bees is her choice. Otherwise, only male drones are hatched. PART 2 : Structure And Function [ 6 marks ] – This section must include 3 labelled diagrams of the human male reproductive system, female reproductive system and the reproductive system of a flower. PARTS OF THE MALE REPRODUCTIVE SYSTEM TESTIS – There are two testes situated in a sac called the scrotum.
Due to the testes needing an optimum temperature for sperm production, the sac is located outside the body. This is because the core body temperature is far too warm to keep producing healthy sperm. EPIDIDYMIS – This stores the large numbers of sperm until they are ejaculated out through the penis. In these two ducts, sperm complete their maturation. SPERM DUCT/VAS DEFERENS – The sperm duct, or vas deferens transport sperm from the testes to the urethra. SEMEN-PRODUCING GLANDS – Semen is the fluid produced to protect the sperm from dehydration and the acidic environment of the female vagina after sexual intercourse.
Semen allows the sperm to swim more easily. URETHRA – This is the tube that normally carries urine from the urinary bladder. When semen containing sperm is ejaculated, it also travels out through the urethra, but the prostate gland enlarges to block of any urine in the urinary bladder at this time. PENIS – The urethra is the tube inside the penis. During sexual intercourse, the spongy cells that surround the urethra fill with blood and the penis becomes firm and erect. The Path That Sperm Travel Testes Epididymis Vas Deferens Urethra PARTS OF THE FEMALE REPRODUCTIVE SYSTEM
OVARY – There are two ovaries. The ovary produces eggs or ova, female sex hormones [oestrogen and progesterone] that regulate the menstrual cycle, pregnancy, and the secondary sexual characteristics, [ e. g. pubic hair, breasts and enlarged hips ] At birth, females have all their eggs formed, but in an immature state. After puberty, and before menopause, one egg is released about every 28 days from each ovary. OVIDUCT/FALLOPIAN TUBE – This connects between the ovary and the uterus. It is also the place where conception or fertilisation of an egg by a sperm occurs.
UTERUS/WOMB – The uterus is a strong muscular and elastic organ where an unborn baby develops. After an egg is released from the ovary, a blood-filled lining develops on the walls of the uterus in preparation for the nourishment of the unborn baby. If no fertilisation of the egg occurs, then this lining passes out through the vagina over seven days as ‘periods’ or menstruation. CERVIX – This is the opening between the uterus and the vagina. During pregnancy, a mucous plug forms across the cervix separating the uterus from the outside to prevent infection of the unborn baby.
This plug falls out and the cervix dilates before the birth of a baby. VAGINA – This is a place where the penis is inserted during sexual intercourse. It is an elastic and muscular organ that expands during birth to allow for the passage of the baby. The Path The Egg Travels Ovary Oviduct/Fallopian Tube Uterus/Womb Cervix Vagina REPRODUCTIVE SYSTEM OF A FLOWER STIGMA – The receptive part of the carpel. Pollen grains will germinate onl if they land here STYLE – The structure that supports the stigma OVARY – The base of the carpel where the ovules develop. ANTHER –
Top portion of the Stamen, the male organ of reproduction. FILAMENT – The slender stalk of the stamen that supports the anther. STAMEN – [ male ] Anther filament CARPEL – [ female] stigma style ovary ovule Part 3 : Fertilisation [ 8 marks ] – Compare in detail the processes of fertilisation in humans and plants. Flowering Plants After the carpel is pollinated, the pollen grain germinates in a response to a sugary fluid secreted by the mature stigma [mainly sucrose]. From each pollen grain, a pollen tube grows out and attempts to travel to the ovary by creating a path through the female tissue.
The vegetative [or tube] and generative nuclei of the pollen grain pass into its respective pollen tube. After the pollen grain sticks to the stigma of the carpel [female reproductive structure] a pollen tube grows and penetrates the ovule through a tiny pore called a micropyle. The pollen tube does not directly reach the ovary in a straight line. It travels near the skin of the style and curls to the bottom of the ovary, then near the receptacle, it breaks through the ovule through the micropyle [an opening in the ovule wall] and the pollen tube “bursts” into the embryo sac.
After being fertilized, the ovary starts to swell and will develop into the fruit. With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule. The growth of the pollen tube is controlled by the vegetative [or tube] cytoplasm. Hydrolytic enzymes are secreted by the pollen tubes that digest the female tissue as the tube grows down the stigma and style; the digested tissue is used as a nutrient source for the pollen tube as it grows.
During pollen tube growth toward the ovary, the generative nucleus divides to produce two separate sperm nuclei [haploid number of chromosomes] – a growing pollen tube therefore contains three separate nuclei, two sperm and one tube. The sperms are interconnected and dimorphic, the large one, in a number of plants, is also linked to the tube nucleus and the interconnected sperm and tube nucleuses form the “male germ unit”. Double fertilization is the process in angiosperms [flowering plants] in which two sperm nuclei from each pollen tube fertilize two cells in an ovary.
After the pollen tube reaches the ovary the pollen tube nucleus disintegrates and the two sperm cells are released into the ovary; one of the two sperm cells fertilizes the egg cell [at the bottom of the ovule near the micropyle], forming a diploid zygote. This is the point when fertilization actually occurs. Note that pollination and fertilization are two separate processes. The other sperm cell fuses with two haploid polar nuclei [contained in the central cell] in the centre of the embryo sac [or ovule]. The resulting cell is triploid.
This triploid cell divides through mitosis and forms the endosperm, a nutrient-rich tissue, inside the seed. Double fertilization occurs only in angiosperm plants. One primitive species of flowering plant, Nuphar polysepala, has endosperm that is diploid, resulting from the fusion of a pollen nucleus with one, rather than two, maternal nuclei. It is believed that early in the development of angiosperm lineages, there was duplication in this mode of reproduction, producing seven-celled/eight-nucleate female gametophytes, and triploid endosperms with a 2:1 maternal to paternal genome ratio.
In many plants, the development of the flesh of the fruit is proportional to the percentage of fertilized ovules. For example, with watermelon, about a thousand grains of pollen must be delivered and spread evenly on the three lobes of the stigma to make a normal sized and shaped fruit. embryo and its surrounding membranes. The term “conception” is not usually used in scientific literature because of its variable definition and connotation. Mammals Usually mammals rely on internal fertilization through copulation.
After a male ejaculates, a large number of sperm cells move to the upper vagina [via contractions from the vagina] through the cervix and across the length of the uterus toward the ovum. The capacitated spermatozoon and the oocyte meet and interact in the middle of the fallopian tube. It is probable that chemotaxis is involved in guiding the sperm to the egg, but the mechanism has yet to be worked out. Fusion between the oocyte plasma membranes and sperm follows, allowing the entry of the sperm nucleus, centriole and flagellum, but not the mitochondria, into the oocyte.
The egg “activates” itself upon fusing with a single sperm cell, thereby changing its cell membrane to prevent fusion with other sperm. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote begins to divide and form a blastocyst and when it reaches the uterus, it performs implantation in the endometrium. At this point the female’s pregnancy has begun. If the embryo implants in any tissue other than the uterine wall, an ectopic pregnancy results, which can be fatal to the mother. PART 4 – Embryo Development ; Nutrition [ 8 Marks ] Compare embryo nutrition in humans and in plants. In plants, the seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant. The formation of the seed completes the process of reproduction in seed plants [ started with the development of flowers and pollination ], with the embryo developed from the zygote and the seed coat from the integuments of the ovule. In humans, nutrition is quite different.
Although everyone needs the same amount on nutrients and minerals, the level of such amounts can vary depending on what life stage the person is in. the nutritional demands of pregnancy are extraordinary due to the baby’s growth depending on getting all minerals and other nutrients, most being in larger amounts. Before falling pregnant, a woman must establish nutrition habits that will optimally nourish a growing foetus. In early pregnancy, the embryo undergoes rapid and significant developmental changes that depend on the mother’s prior balance of minerals, vitamins and other nutrition.
Men don’t get off lightly either. Before conception, it is said their nutrition needs to be in check also, to ensure the best transit of genetics into the fertilisation. One major reason, among many others for the mothers nutrition to be ultimate before falling pregnant determines whether the uterus will be able to support the growth of a healthy placenta during the first month of gestation. If the placenta works perfectly, the foetus wants/needs nothing, If it doesn’t however, there is no alternative source of nourishment available, giving the foetus a limited chance to thrive.
Essentially, the placenta is the baby’s only lifeline. The placenta is a cushion of tissue in which the mother’s and baby’s blood vessels intertwine and exchange materials. The blood never mixes, but nutrients and oxygen cross while wastes are passed through to mum, therefore being excreted by her also. The amniotic sac is formed essentially to cradle the baby from outside sounds and abrupt movement. All shock is cushioned by fluids. The placenta is a highly metabolic organ, with around 60 sets of enzymes of its own.
This means it is able to actively gather hormones, nutrients and protein molecules such as antibodies alike, transferring them to baby’s bloodstream. If the mother is undernourished, and her placenta is weak, her child may not hold nutrients in later life, and if the child born is a girl, she may miss out on the change to develop a placenta of her own when she falls pregnant herself. The single, most critical nutrition period in a pregnancy generally occurs before a woman even knows she is pregnant. – Give an outline of the different stages of embryo development in humans and plants.
HUMAN EMBRY DEVELOPMENTAbout 1 month before conception: The sperm take a month or so to travel from a testicle, through a long tube called the “vas deferens,” to reach a small reservoir inside the man’s prostate gland. Here, semen (a mixture of spermatozoa and various fluids) is formed. Each spermatozoon contains human DNA. | Perhaps one day before conception: The woman ovulates and produces one mature ovum (egg cell). It travels down one of her fallopian tubes towards her uterus. | At conception: One very lucky spermatozoon out of hundreds of millions ejaculated by the man may penetrate the outside layer of the ovum and fertilize it.
This happens typically in the upper third of one of the woman’s Fallopian tubes. The surface of the ovum changes its electrical characteristics and normally prevents additional sperm from entering. A genetically unique entity is formed shortly thereafter, called a zygote. This is commonly referred to as a “fertilized ovum. ” However that term is not really valid because the ovum ceases to exist after conception. The zygote “… is biologically alive. It fulfils the four criteria needed to establish biological life: 1. metabolism, 2. growth, 3. eaction to stimuli, and 4. reproduction. ” The zygote first divides into two identical cells, called blastomeres. They continue to subdivide once every 12 to 20 hours as the zygote slowly passes down the fallopian tubes. | About 3 days after conception: The zygote now consists of 16 cells and is called a 16 cell morula (a. k. a. pre-embryo). It has normally reached the junction of the fallopian tube and the uterus. | 5 days or so after conception: A cavity appears in the center of the morula. The grouping of cells are now called a blastocyst.
It has an inner group of cells which will become the fetus and later the newborn; it has an outer shell of cells which will “become the membranes that nourish and protect the inner group of cells. ” 3 It has traveled down the fallopian tubes and has started to attach itself to the endometrium, the inside wall of the uterus (a. k. a. womb). | 9 or 10 days after conception: The blastocyst has fully attached itself to endometrium. Primitive placental blood circulation has begun. This blastocyst has become one of the lucky ones. The vast majority of ova are never fertilized and make it this far in the process. 12 days or so after conception: The blastocyst has started to produce hormones which can be detected in the woman’s urine. If instructions are followed exactly, a home-pregnancy test may reliably detect pregnancy at this point, or shortly thereafter. | 13 or 14 days after conception: A “primitive streak” appears. It will later develop into the fetus’ central nervous system. The pre-embryo is now referred to as an embryo. It is a very small cluster of undifferentiated tissue at this stage of development. | 3 weeks: The embryo is now about 1/12″ long, the size of a pencil point.
It most closely resembles a worm – long and thin and with a segmented end. Its heart begins to beat about 18 to 21 days after conception. Before this time, the woman might have noticed that her menstrual period is late; she might suspect that she is pregnant and conduct a pregnancy test. | 4 weeks: The embryo is now about 1/5″ long. It looks something like a tadpole. The structure that will develop into a head is visible, as is a noticeable tail. The embryo has structures like the gills of a fish in the area that will later develop into a throat. | 5 weeks: Tiny arm and leg buds have formed.
Hands with webs between the fingers have formed at the end of the arm buds. Fingerprints are detectable. The face “has a distinctly reptilian aspect. ” 1 “… the embryo still has a tail and cannot be distinguished from pig, rabbit, elephant, or chick embryo. ” | 6 weeks: The embryo is about 1/2″ long. The face has two eyes on each side of its head; the front of the face has “connected slits where the mouth and nose eventually will be. ” | 7 weeks: The embryo has almost lost its tail. “The face is mammalian but somewhat pig-like. ” 1 Pain sensors appear. Many conservative Christians believe that the embryo can feel pain.
However, the higher functions of the brain have yet to develop, and the pathways to transfer pain signals from the pain sensors to the brain are not in place at this time. | 2 months: The embryo’s face resembles that of a primate but is not fully human in appearance. Some of the brain begins to form; this is the primitive “reptilian brain” that will function throughout life. The embryo will respond to prodding, although it has no consciousness at this stage of development. The brain’s higher functions do not develop until much later in pregnancy when the fetus becomes sentient. | 0 weeks: The embryo is now called a fetus. Its face looks human; its gender may be detectable via ultrasound. | 13 weeks or 3 months: The fetus is about 3 inches long and weighs about an ounce. Fingernails and bones can be seen. | 17 weeks or 3. 9 months: It is 8″ long and weighs about a half pound. The fetus’ movements may begin to be felt. Its heartbeat can usually be detected. | 22 weeks or 5 months: 12″ long and weighing about a pound, the fetus has hair on its head. Its movements can be felt. Half-way through the 22nd week, the fetus’ lungs may be developed to the point where it would have a iniscule chance to live on its own. State laws and medical association regulations generally outlaw almost all abortions beyond 20 or 21 weeks gestation. “A baby born during the 22nd week has a 14. 8 percent chance of survival. And about half of these survivors are brain-damaged, either by lack of oxygen (from poor initial respiration) or too much oxygen (from the ventilator). Neonatologists predict that no baby will ever be viable before the 22nd week, because before then the lungs are not fully formed. ” 4 Of course, if someone develops an artificial womb, then this limit could change suddenly. | 6 weeks or 6 months: The fetus 14″ long and almost two pounds. The lungs’ bronchioles develop. Interlinking of the brain’s neurons begins. The higher functions of the fetal brain turn on for the first time. Some rudimentary brain waves indicating consciousness can be detected. The fetus will probably be able to feel pain for the first time. It has become conscious of its surroundings. The fetus has become a sentient human life for the first time. | 7 months: 16″ long and weighing about three pounds. Regular brain waves are detectable which are similar to those in adults. | 8 months: 18″ long and weighing about 5 pounds. 9 months: 20″ long and with an average weight of 7 pounds, a full-term fetus’ is typically born about this time. | PART 5 – Reproductive Technology [4 marks] – Provide 2 newspaper articles from 2008/2009 discussing reproductive technology. ARTICLE ONE In vitro fertilization (IVF) Modern IVF generally involves controlled ovarian hyper stimulation with exogenous gonadotropins, harvesting the eggs via transvaginal ultrasonographic-guided aspiration, co-culture of eggs and sperm in culture (or intracytoplasmic injection of sperm into the oocyte), and placement of the resultant zygotes (2-5 d later) directly into the uterus.
The first IVF pregnancy was achieved in 1978. Since then, the number of IVF centers and IVF procedures performed has increased dramatically. An intense effort to obtain insurance coverage for these services has also occurred. With the support of organizations such as RESOLVE (ie, the National Fertility Association), 15 US states provide coverage for these services. Currently, 3 states (Massachusetts, New Jersey, and Rhode Island) offer full coverage. Other states exempt health maintenance organization programs, private insurers, or companies with few employees. Other states offer limits to their coverage.
In states that provide full coverage, the actual cost per paid subscriber is not substantial. A recent study in Massachusetts calculated that the increase is only $25 per year per subscriber. As a result of the Fertility Clinic Success Rate and Certification Act, the US Centers for Disease Control and Prevention (CDC) gathers information from 422 of the 475 clinics throughout the United States. Information from 2005 shows that 134,260 assisted reproductive technique (ART) cycles were performed resulting in 38,910 live births (deliveries of one or more living infants) and 52,041 infants.
Other assisted reproductive techniques Gamete intrafallopian transfer (GIFT) was developed in 1984 for women with unexplained infertility. GIFT is much less utilized, but to certain religious and ethnic communities (in which fertilization inside the woman’s body is the only type allowed), it is considered more acceptable. During this procedure, the patient undergoes a controlled ovarian hyperstimulation. The oocytes are retrieved transvaginally under ultrasonographic guidance, and 3-4 oocytes are placed via laparoscopy into one of the fallopian tubes along with sperm.
During zygote intrafallopian transfer (ZIFT), oocytes are retrieved similar to IVF and GIFT and they are allowed to fertilize in vitro in the laboratory as in IVF. A day after fertilization (2 cell stage), 3-4 embryos are transferred via laparoscopy into one of the fallopian tubes. If the embryos are allowed to develop to greater than a 2-cell stage, the procedure is termed tubal embryo transfer (TET). The only benefit to a ZIFT or TET versus the more traditional IVF is for women who are thought to have compromised embryo quality due to embryo in vitro culture.
Placing these zygotes or embryos back into their own natural incubators is thought to enhance subsequent development with improved pregnancy rates. With the development of enhanced culture media, the success rates for IVF are now comparable, if not better, to those of GIFT and ZIFT, and IVF is less invasive than GIFT and ZIFT. Interpreting IVF success rates Comparing one program’s success rate to another is difficult because of all the variables involved, including the program’s selection criteria, patient demographics, and insurance coverage.
In general, like any statistical analysis, the more IVF cycles a program has performed, the more valid the numbers are. The cancellation rate is a critical number. If the rate is high, the program is possibly very selective for the patients it allows to proceed to egg retrieval. This type of program would rather cancel the patient’s procedure than have a low chance for success. The implantation rate refers to the pregnancy rate divided by the number of embryos transferred.
If the implantation rate is low and the pregnancy rate is high, this suggests that the program is transferring a large number of embryos per patient to achieve that success. Chances are good that the program’s multiple pregnancy (eg, twins, triplets, and higher order multiples) rate is high. Optimally, the better programs have a low cancellation rates, good pregnancy and implantation rates, and high singleton pregnancy rates compared with multiple pregnancy rates. The ultimate critical number is the birth rate because this represents the final goal of the patient and the physician.
This goal is also less vulnerable to misinterpretation than the pregnancy rate (single positive HCG vs serial increases) or the clinical pregnancy rate (gestational sac vs fetal pole vs fetal pole with heartbeat). IVF outcomes 2005 data for IVF outcomes are summarized and results can be viewed on the CDC and Society for Assisted Reproductive Technology Web sites. Outcomes are stratified based on cycle type (fresh IVF, frozen embryo IVF, donor IVF, and maternal age). Overall, 134,260 ART cycles were performed in the United States in 2005 resulting in 38,910 live birth deliveries. For reference, in 996, 14,507 deliveries resulted from 64,681 ART cycles. Because more than 1 infant is born during a live-birth delivery (eg, twins) in some cases, the total number of infants born is larger than the number of live-births. From 1996-2005, the percentage of transfers resulting in live births for fresh–nondonor cycles increased from 28% in 1996 to 34% in 2005. ARTICLE TWO Some parents would love the chance to decide, while others wouldn’t dream of meddling with nature. The medical world is also divided. Professional groups say sex selection is allowable in certain situations, but differ as to which ones.
Meanwhile, it’s not illegal, and some doctors are already cashing in on the demand. There are several ways to pick a baby’s sex before a woman becomes pregnant, or at least to shift the odds. Most of the procedures were originally developed to treat infertility or prevent genetic diseases. The most reliable method is not easy or cheap. It requires in vitro fertilization, in which doctors prescribe drugs to stimulate the mother’s ovaries, perform surgery to collect her eggs, fertilize them in the laboratory and then insert the embryos into her uterus.
Before the embryos are placed in the womb, some doctors will test for sex and, if there are enough embryos, let the parents decide whether to insert exclusively male or female ones. Pregnancy is not guaranteed, and the combined procedures can cost $20,000 or more, often not covered by insurance. Many doctors refuse to perform these invasive procedures just for sex selection, and some people are troubled by what eventually becomes of the embryos of the unwanted sex, which may be frozen or discarded. Another method, used before the eggs are fertilized, involves sorting sperm, because it is the sperm and not the egg that determines a baby’s sex.
Semen normally has equal numbers of male- and female-producing sperm cells, but a technology called MicroSort can shift the ratio to either 88 percent female or 73 percent male. The “enriched” specimen can then be used for insemination or in vitro fertilization. It can cost $4,000 to $6,000, not including in vitro fertilization. MicroSort is still experimental and available only as part of a study being done to apply for approval from the Food and Drug Administration. The technology was originally developed by the Agriculture Department for use in farm animals, and it was adapted for people by scientists at the Genetics and IVF
Institute, a fertility clinic in Virginia. The technique has been used in more than 1,000 pregnancies, with more than 900 births so far, a spokesman for the clinic said. As of January 2006 (the most recent figures released), the success rate among parents who wanted girls was 91 percent, and for those who wanted boys, it was 76 percent. Regardless of the method, the American College of Obstetricians and Gynecologists opposes sex selection except in people who carry a genetic disease that primarily affects one sex.
But allowing sex selection just because the parents want it, with no medical reason, may support “sexist practices,” the college said in an opinion paper published this month in its journal, Obstetrics and Gynecology. Some people say sex selection is ethical if parents already have one or more boys and now want a girl, or vice versa. In that case, it’s “family balancing,” not sex discrimination. The MicroSort study accepts only people who have genetic disorders or request family balancing (they are asked for birth records), and a company spokesman said that even if the technique was approved, it would not be used for first babies.
The obstetricians group doesn’t buy the family-balance argument, noting that some parents will say whatever they think the doctor wants to hear. The group also says that even if people are sincere about family balance, the very act of choosing a baby’s sex “may be interpreted as condoning sexist values. ” Much of the worry about this issue derives from what has happened in China and India, where preferences for boys led to widespread aborting of female fetuses when ultrasound and other tests made it possible to identify them. China’s one-child policy is thought to have made matters worse.
Last month, Chinese officials said that 118 boys were born for every 100 girls in 2005, and some reports have projected an excess of 30 million males in less than 15 years. The United Nations opposes sex selection for nonmedical reasons, and a number of countries have outlawed it, including Australia, Canada and Britain, and other nations in Asia, South America and Europe. Left unanswered is the question of whether societies, and families, that favor boys should just be allowed to have them, since attitudes are hard to change, and girls born into such environments may be abused.
The American Society for Reproductive Medicine, a group for infertility doctors, takes a somewhat more relaxed view of sex selection than does the college of obstetricians. Instead of opposing sex selection outright, it says that in people who already need in vitro fertilization and want to test the embryos’ sex without a medical reason, the testing should “not be encouraged. ” And those who don’t need in vitro fertilization but want it just for sex selection “should be discouraged,” the group says.
But sperm sorting is another matter, the society says. It is noninvasive and does not involve discarding embryos of the “wrong” sex. The society concludes that “sex selection aimed at increasing gender variety in families may not so greatly increase the risk of harm to children, women or society that its use should be prohibited or condemned as unethical in all cases. ” The group also says it may eventually be reasonable to use sperm sorting for a first or only child. Dr.
Jamie Grifo, the program director of New York University’s Fertility Center, said that he opposed using embryo testing just for sex selection, but that it was reasonable to honor the request in patients who were already having embryos screened for medical reasons, had a child and wanted one of the opposite sex. In those cases, he said, the information is already available and doesn’t require an extra procedure. “It’s the patient’s information, their desire,” he said. “Who are we to decide, to play God? I’ve got news for you, it’s not going to change the gender balance in the world. We get a handful of requests per year, and we’re doing it.
It’s always been a controversy, but I don’t think it’s a big problem. We should preserve the autonomy of patients to make these very personal decisions. ” Dr. Jeffrey M. Steinberg, from Encino, Calif. , who has three clinics that offer sex selection and plans to open a fourth, in Manhattan, said: “We prefer to do it for family balancing, but we’ve never turned away someone who came in and said, ‘I want my first to be a boy or a girl. ’ If they all said a boy first, we’d probably shy away, but it’s 50-50. ” “Reproductive choice, as far as I’m concerned, is a very personal issue,” Dr. Steinberg said. If it’s not going to hurt anyone, we go ahead and give them what they want. ” Many patients come from other countries, he said. John A. Robertson, a professor of law and bioethics at the University of Texas, said: “The distinction between doing it for so-called family balancing or gender variety would be a useful line to draw at this stage of the debate, just as maybe a practice guideline, and let’s just see how it works out. ” In the long run, Mr. Robertson said, he doubted that enough Americans would use genetic tests to skew the sex balance in the population, and he pointed out that so far, sperm sorting was more successful at roducing girls than boys. He concluded, “I think this will slowly get clarified, and people will see it’s not as big a deal as they think. ” SUMMARY IVF is a shiny new way to conceive kids for those who have unexplained infertility. There are several ways to pick a baby’s sex before a woman becomes pregnant, or at least to shift the odds. Most of the procedures were originally developed to treat infertility or prevent genetic diseases. The most reliable method is not easy or cheap.
It requires in vitro fertilization or IVF, in which doctors prescribe drugs to stimulate the mother’s ovaries, perform surgery to collect her eggs, fertilize them in the laboratory and then insert the embryos into her uterus. This method of fertilization has a more than reasonable success rate, with Information from 2005 shows that 134,260 assisted reproductive technique cycles were performed resulting in 38,910 live births. BIBLIOGRAPHY www. google. com www. wikipedia. com. au www. emedicine. medscape. com/article/263907-overview [ Article One ] www. nytimes. com Nelson Biology VCE Units 1;2 Encyclopaedia Brittanica
