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Suppose a sperm fertilized a 2nd polar body( haploid) is there a chance of somewhat normal development?
The 2nd polar body contains almost no cytoplasm, so if only this body is fertilized it contains no maternal genes to guide the development and moreover not enough nutrients. So this wouldn't work. "Source" Moreover, there wasn't reported even any case of "twin" resulting from the fertilization of 2nd polar body according to this article
There was reported case of twins formed by a mass of fertilized ovum and fertilized (diploid) first polar body. Source
What could happen is that if both polar body and oocyte are fertilized, these two cells merge and form tetraploid embryo. Which is sometimes able to form fetus (sometimes just ends as mola hydatinosa), but definitely not able to produce a viable child in humans.
Mpribis is 99% correct, except that the polar body does indeed contain the same amount of maternal genes as the secondary oocyte (remember, it's the product of the second division--from diploid to haploid). But like Mpbris said, since the second polar body is nutrient-poor, and lacks full complement of organelles, the odds of it remaining viable if it were fertilized are vanishingly small. Such "polar body twinning" is theoretically possible, but has yet to be documented as of the the time of my writing this.
Preimplantation Genetic Diagnosis
23.2.2 Polar Body Biopsy
Polar bodies (PBs) are produced in the first and second meiotic division as oocytes complete maturation upon fertilization. PB analysis represents an indirect method in which the genotype or chromosomal constitution of the oocyte is derived from the complement present in the PBs. An accurate diagnosis should be based on an analysis of both the first and second PBs to preclude a misdiagnosis, which may arise from recombination or allele dropout (ADO) (monogenic diseases) or by nondisjunction or meiotic errors (chromosomal analysis). The doubling of the total sample number together with the fact that some oocytes fail to fertilize or form embryos may be regarded as a waste of time and resources unless the PB samples can be stored, and only those corresponding with normal embryo development are ultimately processed.
For PB biopsy, the ZP is breached using either mechanical slitting with a fine needle or laser technology, as the acidic Tyrode's solution may adversely affect subsequent oocyte development. Although both PBs may be biopsied simultaneously (requiring only one manipulation), it may be difficult to differentiate them morphologically, and sequential biopsy has been recommended to ensure a correct PB identification ( Treff et al., 2012 ).
The advantages of PB biopsy are self-evident: as PBs do not contribute to normal fertilization or embryonic development, their removal has no detrimental effects. In countries where genetic testing should be finished before syngamy, PB biopsy is the only legal option, but it leaves very little time to complete diagnosis. Conversely, if legal restrictions or ethics are not an issue, more time is available for analysis compared with a cleavage-stage biopsy. The most important limitation of PB biopsy is that only the maternal genetic contribution can be evaluated.
Oocyte biology and genetics revelations from polar bodies
The enormous volume of the fertilized egg is attributable to the suppression of cleavage during oocyte growth and the unequal cleavages during the first and second meiotic divisions. The two products of these divisions are the diminutive polar bodies (PB), which contain a redundant set of chromosomes/chromatids plus cytoplasmic organelles. The PB have strictly limited but differential life spans while viable they possess the genetic potential to support normal embryonic development after transfer to a cytoplast. In addition to the theoretical possibility of using this non-cloning technique to generate more embryos, polar bodies can be used for genetic testing. By cytogenetic analysis of both PB using fluorescent in-situ hybridization (FISH) or chromosome painting, partial or full chromosomal status in the oocyte can be predicted this approach finds particular application for women of advanced reproductive age as well as with maternally inherited translocations and single gene defects. By studying both of the PB, potential problems of interpretation arising from allele dropout can be reduced a heterozygous first polar body provides the least ambiguous result. Mitochondria segregate randomly during meiotic cleavages providing an opportunity also to use the PB to screen for mitochondrial mutations and deletions. Thus, the PB can serve useful diagnostic purposes, especially where pre-fertilization screening or avoidance of embryo biopsy is desirable.
What is a Polar Body? (with picture)
A polar body, sometimes referred to as a polar cell, is a cell found within the ovum of mammals as well as plants. It is the byproduct of the natural process of cell division during oogenesis and meiosis. Oogenesis is the process by which ova are created, and meiosis is the division of the cells at the time of ovulation, when the ovum is released into the fallopian tubes, and an additional division just after fertilization. In mammals, it is not a functional reproductive cell, and it disintegrates after a period of time, but in plants, the polar body performs a separate function in the development of the resulting offspring.
During meiosis, the number of chromosomes in germ cells are split in half to produce reproductive cells, or gametes. When the female reproductive cell, or ovum, joins with the male reproductive cell, or sperm, the correct full number of chromosomes is regained. The polar body is the other half of the developing female cell, also containing half the required number of chromosomes. However, it does not contain sufficient cytoplasm to function as a full-fledged reproductive cell, because during meiosis, the cytoplasm is distributed into the ovum during a process called cytokinesis. In mitosis, the process that leads to two separate body cells with a full complement of chromosomes, cytokinesis divides the cytoplasm evenly.
In plants, the fertilization process involves both the ovum and the polar bodies. When the ovum is fertilized by the plant's male gamete, the polar bodies also are fertilized by a second male cell. They then develop not into a plant but into endosperm, a cell structure that functions to produce nutrients for the growing plant cell. Endosperm not only helps nourish the growing plant, it also makes seeds and grains highly nutritious for consumption by other animals, including humans.
It has been theorized that something similar might occur within mammals, if two sperm fertilized both the egg and a polar body. This theoretical occurrence is called polar body twinning. Some scientists believe viable twins could be produced through this process, but others believe that the polar body, with its lack of sufficient cytoplasm, would not be able to develop properly. If twinning were possible, the resulting offspring would not be identical twins, because they would share the genes of the mother but would theoretically carry genetic material from two different sperm.
At birth, a female&rsquos ovaries contain all the eggs she will ever produce. However, the eggs do not start to mature until she enters puberty. After menarche, one egg typically matures each month until a woman reaches middle adulthood.
The process of producing eggs in the ovary is called oogenesis. Eggs, like sperm, are haploid cells, and their production occurs in several steps that involve different types of cells, as shown in Figure below. You can follow the process of oogenesis in the figure as you read about it below.
Oogenesis. Oogenesis begins before birth but is not finished until after puberty. A mature egg forms only if a secondary oocyte is fertilized by a sperm.
Oogenesis begins long before birth when an oogonium with the diploid number of chromosomes undergoes mitosis. It produces a diploid daughter cell called a primary oocyte. The primary oocyte, in turn, starts to go through the first cell division of meiosis (meiosis I). However, it does not complete meiosis until much later. The primary oocyte remains in a resting state, nestled in a tiny, immature follicle until puberty.
Maturation of a Follicle
Beginning in puberty, each month one of the follicles and its primary oocyte starts to mature (also see Figure below). The primary oocyte resumes meiosis and divides to form asecondary oocyte and a smaller cell, called a polar body. Both the secondary oocyte and polar body are haploid cells. The secondary oocyte has most of the cytoplasm from the original cell and is much larger than the polar body.
Maturation of a Follicle and Ovulation. A follicle matures and its primary oocyte (follicle) resumes meiosis to form a secondary oocyte in the secondary follicle. The follicle ruptures and the oocyte leaves the ovary during ovulation. What happens to the ruptured follicle then?
Ovulation and Fertilization
After 12&ndash14 days, when the follicle is mature, it bursts open, releasing the secondary oocyte from the ovary. This event is called ovulation (see Figure above). The follicle, now called acorpus luteum, starts to degenerate, or break down. After the secondary oocyte leaves the ovary, it is swept into the nearby fallopian tube by the waving, fringelike end (see Figure below).
Egg Entering Fallopian Tube. After ovulation, the fringelike end of the fallopian tube sweeps the oocyte inside of the tube, where it begins its journey to the uterus.
If the secondary oocyte is fertilized by a sperm as it is passing through the fallopian tube, it completes meiosis and forms a mature egg and another polar body. (The polar bodies break down and disappear.) If the secondary oocyte is not fertilized, it passes into the uterus as an immature egg and soon disintegrates.
Probing Polar Bodies to Pick Disease-Free Embryos
A polar body is to an oocyte what a moon is to a planet. (NASA)
After writing eleven editions of a human genetics textbook, I automatically assign chapter numbers to exciting new findings. But the 3-page case report in this week&rsquos JAMA Neurology on selecting disease-free embryos tangled up my brain with all its connections.
The case report delves into:
a. Meiosis, including polar bodies
b. Mendel&rsquos first law
e. Protein folding
f. Assisted reproductive technologies (ARTs)
i. All of the above
The researchers (Alice Uflacker and Murali Doraiswamy from the Duke Institute for Brain Science, Svetlana Rechitsky and Ilan Tur-Kaspa from the Reproductive Genetics Institute in Chicago, and Michael Geschwind and Tricia See from UCSF) describe using ARTs to enable a woman whose relatives have a devastating and very rare brain disease to have children free of the family legacy.
AN INHERITED PRION DISEASE
The disease, Gerstmann-Straussler-Scheinker Syndrome (GSS), affects only 1-10 per 100 million births. Much of what&rsquos known about it comes from an 8-generation family from Indiana that has had 57 affected members.
GSS is a prion disorder, but one that is inherited rather than acquired from eating tainted burgers from mad cows (bovine spongiform encephalopathy) or the brains of dead people (kuru). A prion is a protein that can exist in several folded forms, one of which is infectious &ndash it makes the other forms like itself. These &ldquorogue proteins&rdquo tend to turn brains into a spongy mess.
Cannibals, Papua New Guinea
Prions were first described in 1954 in sheep afflicted with scrapie, but farmers had reported it since the Middle Ages. Chronicling of kuru among the Fore people of Papua New Guinea was the life&rsquos work of D. Carleton Gajdusek, from the 1950s for many years before his legal woes. I tell the curious history of prions in chapter 4 of my essay book Discovery: Windows on the Life Sciences (Blackwell Science). (It was poorly marketed into oblivion.)
Women and children Fore infected themselves when they ate the raw brains of dead friends and relatives to honor them. The men got safe cooked parts, mostly muscle, and wives of dead warriors ate the penises, cooked I presume. You can read the gory story in Dr. Gajdusek&rsquos Nobel speech. Then in the 1980s came the notorious stumbling bovines of England.
Because a prion is a protein, it&rsquos encoded by a gene &mdash the prion protein gene (PrP) on chromosome 20. Mutations at different places in the gene cause different inherited prion disorders, all of which are exceedingly rare.
Creutzfeldt-Jakob disease (CJD) is like mad cow. Fatal familial insomnia (FFI) is an inherited prion disease that may have inspired an illness among the crew of the USS Enterprise in Star Trek: The Next Generation (&ldquoNight Terrors,&rdquo which aired March 16, 1991, Stardate 19144631.2) The ship&rsquos wandering into a rift in space deprived crew members of dream sleep, causing terrifying hallucinations and extreme paranoia. But unlike Commander Riker and colleagues, people with FFI do not sleep at all. Nor do they recover at the end of the episode.
GSS progresses from memory loss and slurred speech to &ldquoprion dementia,&rdquo uncontrollable movements, limb weakness, and sometimes deafness and/or blindness. Gummy prion protein is deposited in the cerebral cortex, the basal ganglia, and especially in the cerebellum, which destroys voluntary movement.
Alice Uflacker, MD, one of the Duke researchers, describes the condition. &ldquoTypical age of onset is the 40s to 50s. Disease progression is longer than that of genetic CJD and FFI. A patient may be symptomatic for about 5 years, leading to death. Because age of onset is past young reproductive age, patients may not be aware that there is a 50% chance of passing the mutation to their offspring. Often times, however, the person at risk has contact with immediate and extended family members and has witnessed their loved ones deteriorate.&rdquo
The patient, Amanda Kalinsky, and her husband and children appeared on the front page of the New York Times on Tuesday.
Because GSS is autosomal dominant, it peppers family pedigrees in each generation, striking men and women. Even people who know their family history may have difficulty finding a physician who has heard of GSS, a problem that unites the rare disease community. Orthopedic surgeons, the specialists usually consulted when symptoms begin, look for common causes (&ldquohorses&rdquo) rather than the rare &ldquozebras.&rdquo
Many physicians also haven&rsquot heard of preimplantation genetic diagnosis (PGD), although it&rsquos been around awhile. The Kalinskys learned about it from a genetic counselor, and elected to have predictive testing so Amanda could learn whether or not her father&rsquos disease lay in her own future. It was a brave decision that few in her position for similar conditions, such as Huntington Disease, make. Now she knows she&rsquoll develop GSS, for the disease has near-complete penetrance &ndash inherit the mutation and you get the disease.
Amanda and her husband didn&rsquot want her genetic fate for their children. And thanks to technology, they had a choice.
Selecting embryos isn&rsquot new &ndash it was first done in 1990 for X-linked mutations. In 1993 researchers selected the embryo that became Chloe O&rsquoBrien, free of the severe cystic fibrosis that affected her brother. In 1994 came another milestone, a girl conceived and selected to provide umbilical cord stem cells to treat her teenage sister&rsquos leukemia, echoed in Jodi Picoult&rsquos novel My Sister&rsquos Keeper. The most famous PGDer was Adam Nash, selected to cure his sister of Fanconi anemia and born in August 2000. I vividly remember the negative vibes against this first &ldquosavior sibling&rdquo family on the Today Show now the choice to have one child to help another isn&rsquot so unusual.
PGD works because of a feature of the early embryos of many animal species called indeterminate cleavage. A cell can be plucked from an 8-celled embryo, tested, and the 7-celled remainder put back into a woman to continue developing, or held over for a few cell divisions. If the 7-celled embryo has the probed mutation, it can be discarded or used in research to study the genesis of the family&rsquos disease. Some people who consider life to begin at conception object to the fate of the unused embryos. But thousands of children have been born without their family&rsquos genetic disease thanks to PGD.
To circumvent objections to testing 8-celled embryos, researchers can use a technique called &ldquosequential polar body analysis.&rdquo Polar bodies are by-products of egg formation that are Nature&rsquos way to pack nutrients and organelles into a gigantic egg, prepping it to support an early embryo. The World Health Organization first suggested genetic testing of polar bodies to infer the genotype of the egg in the early 1980s. The intervention destroys the polar bodies, but they serve no function once they&rsquove siphoned off extra genomes and built up the egg. They&rsquore expendable.
Although both sperm and eggs carry only one copy of the genome so fertilization can restore the double number, their timetables are markedly different. Sperm develop quickly and equally. That&rsquos not the case for the female cells.
Technically, the female cell is called an oocyte until it&rsquos a fertilized ovum, so there&rsquos really no such thing as a lone ovum. Oocytes jettison parts of themselves as they form by a double division (meiosis), yielding one huge oocyte and three much smaller cells, the polar bodies. Each of these four cells houses a single genome. In fact, researchers from Harvard and Peking University have already sequenced polar body genomes to infer the genome sequence of the oocytes to which they cling. The name &ldquopolar body&rdquo is celestial and not ursine, because a polar body is like a moon that travels along with its planet.
The &ldquopolar&rdquo in polar body is a celestial reference, not an ursine one.
The jettisoned polar bodies hold important clues, because as chromosome pairs part, a mutation that ends up in a polar body doesn&rsquot end up in the all-important oocyte, or vice versa. This is the physical basis of Gregor Mendel&rsquos observation of the segregation of traits in pea plants. So researchers can test the genes of a polar body to deduce which gene variants made it into the oocyte &ndash in the case of Amanda Kalinsky, the GSS mutation or the normal version of the gene.
The researchers looked at the prion protein gene and 5 markers bracketing it on chromosome 20 in the polar bodies hanging onto some of Amanda&rsquos retrieved oocytes. A different set of markers accompanied the mutant PrP gene and its normal (&ldquowild type&rdquo) version, so they could be distinguished.
But there&rsquos more. Female meiosis actually spawns two sets of polar bodies, at each of the two stages of the division. Examining the markers of the later-released polar bodies can reveal whether the genes on the chromosomes swap parts, called crossing over. If so, then a false negative or false positive oocyte choice could result. A paper from 2011 from Anver Kuliev and Svetlana Rechitsky (who is on the JAMA Neurology paper) reports polar body testing for 938 cycles for 146 different single-gene diseases, resulting in 345 healthy children. It works. But it isn&rsquot really a way to avoid intervening in prenatal development.
Let&rsquos return to the issue of timing. The first meiotic division happens when an oocyte pops out of an ovary sometime after puberty. But the second meiotic division occurs as fertilization happens. So probing polar bodies to catch those confusing crossovers, while a valid and earlier substitute for the 8-cell-stage PGD, happens at the exact time of fertilization. And as I know well from the personal name-calling that followed my recent DNA science post When Does a Human Life Begin? 17 Timepoints, many people do consider a merged sperm and egg to be a full-fledged person, equivalent to say a 53-year-old accountant. Shifting the time of selection to the very beginning of development, to a single cell, might not make a difference to them.
Anyway, the polar body technique, validated with 8-cell-stage PGD, served the Kalinskys well. The researchers injected sperm into 14 oocytes (a refinement of IVF called ICSI, for intracytoplasmic sperm injection), lost a few along the way, but the polar body testing indeed revealed a crossover event that could have led to a mistake. Three beautiful children free of GSS ultimately resulted &ndash 3-year-old twins and a baby, shown on the front page of the New York Times.
THE TOUGH QUESTIONS
The media focused much more on gathering bioethicists for comments than on explaining polar body biology or prions, so I&rsquoll just touch on those issues, since I teach &ldquogenethics&rdquo:
&bull Should an embryo be rejected because it has inherited a disease that won&rsquot cause symptoms for half a century? That question has been raised for the BRCA genes, even more controversial because they confer susceptibility to treatable conditions.
&bull The slippery slope. Will we slide from preventing future people from having deadly brain diseases to choosing trivial traits? We already have. PGD is misused in sex selection.
&bull Are all these manipulations eugenic? Not by intent, but perhaps in consequence. Eugenics has a societal goal, and can be negative (kill the imperfect) or positive (reward the perceived best for reproducing). Medical genetics aims to alleviate suffering at the individual and family levels, but some interventions will ultimately affect the gene pool.
This landmark report on the rarest-of-the-rare Gerstmann&ndashSträussler&ndashScheinker syndrome, a unicorn among the zebras, provides some assurance that for those electing to choose embryos that have won the genetic roulette and not inherited the family&rsquos disease, results are reliable, and can be done before the fertilized ovum divides.
Polar body-based preimplantation genetic diagnosis for Mendelian disorders
Introduced >20 years ago, the use of polar bodies (PBs), involving sequential removal and genetic analysis of the first (PB1) and second (PB2) PB, provides the option for pre-embryonic diagnosis, when the objection to the embryo biopsy procedures makes preimplantation genetic diagnosis (PGD) non-applicable. PB-based approach has presently been utilized in PGD for genetic and chromosomal disorders, applied either separately, or together with embryo biopsy approaches, especially if there are two or more PGD indications. We present here the world's largest experience of 938 PGD cycles for single-gene disorders performed by PB testing for 146 different monogenic conditions, which resulted in the birth of 345 healthy children (eight pregnancies are still ongoing), providing strong evidence that PB-based PGD is a reliable and safe procedure, with an extremely high accuracy rate of over 99%. With application of microarray technology, PB-based approach will be utilized for increasing number of indications, involving simultaneous testing for 24 chromosomes and single-gene disorders.
What is a Barr Body?
Barr body is the name given to the X chromosome that is inactive during the expression of the genes of somatic cells of females. Barr bodies are absent in normal males. Murray Barr discovered this inactive X chromosome in female somatic cells. Barr body is in the state of heterochromatin which is a transcriptionally inactive structure while the other copy, active X chromosome, is in the euchromatin state. Once the Barr body is packaged into heterochromatin, it is not easily accessible to molecules involved in transcription.
Since all females have two X chromosomes, X inactivation or lyonization is important in order to prevent them from having twice as many X chromosome gene products as males. In short, Barr body production ensures that only the necessary amount of genetic information is expressed in females, rather than doubling it. Therefore, throughout the cell’s whole life, one X chromosome of all somatic cells remains silent.
Males can produce sperm when they reach puberty at the age between 10-16 years old. Approximately 200 million sperms produce in a day. These sperms happen in the seminiferous tubules of the testes of male. In this case, the seminiferous tubules are separated by the blood-testis barrier from the systematic circulation.
The spermatogenesis is a process to produce sperms which occurs in the male gonads or testes. The human testes consist of many seminiferous tubules which are lined by the cells of germinal epithelium.
This germinal epithelium plays an important role to produce sperms through the process of spermatogenesis. The germinal cell also contains some somatic cells, known as sertoli cells which have a role in nourishing the developing spermatozoa or sperms.
Image Showing Spermatogenesis Process: Image credit-wikimedia commons
The spermatogenesis is a continuous process and it can be described in four different headings:
Getting confused on # of polar bodies oogenesis / fertilization
^ in this picture there are 3 polar bodies and 1 ovum after fertilization. why in books do they only talk about first and second polar body? why does the first polar body (according to pic) make a copy of itself? does that mean you end up with 3 polar bodies and 1 ovum? thanks!
Commenting because I also have the same question that I've been struggling with for ages and I'm hoping someone has the answer
so my understanding was that the polar bodies still have DNA and are still able to divide. the only difference between them and the ovum is the unequal distribution of things like RNA/cytoplasm/etc but because the polar bodies still have nuclei, there's no reason they can't divide. they just often die soon after because they lack these extra important factors