Saber Prime wrote:Sledge wrote:Saber, I'm not asking you to explain your rubbish, I'm asking you to prove it. Every book, website, piece of research I've ever encountered on the subject says you're wrong. Cite your source, or admit you made a boo boo.
I gave you a scourse a few pages back. Go to a local high school, pick up a science book, read up on DNA.
My Elementry school sucked and was lacking the money department but my high school sure wasn't.
Sonora Uninion High School graduate thank you verry much.
Make sure it's up to date information too. The information you're getting sounds like it came from 30 something years ago.
Look like your High school sucked too because I just got this from my daughters JR.High School book online text books web site.
And its from the 2007 edition of the book and it took me almost an hour to down load the whole book.
Identical twins.
Identical twins occur when a single egg is fertilized to form one zygote (monozygotic) which then divides into two separate embryos. Although their traits and physical appearances are not exactly the same due to environmental conditions both in and outside the womb, they do have identical DNA. This is not considered to be a hereditary trait, but rather an anomaly that occurs in birthing at a rate of about 3 in every 1000 deliveries worldwide, regardless of ethnic background. The two embryos develop into fetuses sharing the same womb. When one egg is fertilized by one sperm cell, and then divides and separates, two identical cells will result. If the zygote splits very early (in the first 2 days after fertilization) they may develop separate placentas (chorion) and separate sacs (amnion). These are called dichorionic, diamniotic (or "di/di") twins, which occurs 20-30% of the time. Most of the time in identical twins the zygote will split after 2 days, resulting in a shared placenta, but two separate sacs. These are called monochorionic, diamniotic ("mono/di") twins.
In about 1% of identical twins the splitting occurs late enough to result in both a shared placenta and a shared sac called; monochorionic, monoamniotic ("mono/mono") twins. Finally, the zygote may split extremely late, resulting in conjoined twins. Mortality is highest for conjoined twins due to the many complications resulting from shared organs. Mono/mono twins have an overall in-utero mortality of about 60%, principally due to cord entanglement prior to 32 weeks gestation. Many times, monoamniotic twins are delivered at 32 weeks electively for the safety of the babies. In higher order multiples, there can sometimes be a combination of fraternal/identical twins.
Mono/di twins have about a 25% mortality due to twin-twin transfusion. Di/di twins have the lowest mortality risk at about 9%, although that is still significantly higher than that of singletons.
Monozygotic twins are genetically identical (unless there has been a mutation in development) and they are usually the same sex. (On rare occasions, Monozygotic twins may express different phenotypes (normally due to an environmental factor or the deactivation of different X chromosomes in monozygotic female twins), and in some extremely rare cases, due to aneuploidy, twins may express different sexual phenotypes, normally due to an XXY Klinefelter's syndrome zygote splitting unevenly. Monozygotic twins generally look alike. Although they do not have the same fingerprints (which are environmental as well as genetic). As they mature, identical twins often become less alike because of lifestyle choices or external influences. Genetically speaking, the children of identical twins are half-siblings rather than cousins. If each member of one set of identical twins marries one member of another set of identical twins then the resulting children would be genetic full siblings. It is estimated that there are around 10 million identical twins and triplets in the world.
The likelihood of a single fertilisation resulting in identical twins appears to be a random event, not a hereditary trait, and is uniformly distributed in all populations around the world.[citation needed] This is in marked contrast to fraternal twinning which ranges from about 6 per thousand births in Japan (almost similar to the rate of identical twins, which is around 4-5) to 15 and more per thousand in some parts of India(and up to 24 in the US, which might mainly be due to IVF, in vitro fertilisation). The exact cause for the splitting of a zygote or embryo is unknown.
Studies have shown that identical twins reared in different environments share similar personality traits, mannerisms, job choices, attitudes, and interests. These findings add to the belief that many behaviors are derived from genes.[citation needed]
Identical twins have identical DNA but differing environmental influences throughout their lives affect which genes are switched on or off. This is called epigenetic modification. A study of 80 pairs of human twins ranging in age from 3 to 74 showed that the youngest twins have relatively few epigenetic differences. The number of epigenetic differences between identical twins increases with age. 50-year-old twins had over three times the epigenetic difference of 3-year-old twins. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference. However, certain characteristics become more alike as twins age, such as IQ and personality. This phenomenon illustrates the influence of genetics in many aspects of human characteristics and behaviour.
A new theory (July 3, 2007) found that identical twins are formed after an embryo essentially collapses, splitting the progenitor cells (those that contain the body's fundamental genetic material) in half. That leaves the same genetic material divided in two on opposite sides of the embryo. Eventually, two separate fetuses develop. The research was presented at a meeting of the European Society for Human Reproduction and Embryology in Lyon, France. Utilizing computer software to take photos every 2 minutes of 33 embryos growing in a laboratory, Dr. Dianna Payne, a visiting research fellow at the Mio Fertility Clinic in Japan, documented for the first time the early days of twin development. Payne also discovered explanation for why in-vitro fertilization techniques are more likely to create twins. Only about 3 pairs of twins per 1,000 deliveries occur as a result of natural conception. But for IVF deliveries, there are nearly 21 pairs of twins for every 1,000.Also, the latest twin study found that ability to listen to 2 things at once is largely inherited. Thus, listening to someone talking, speech entering the right ear travels in large part to the left side of the brain, where language is processed. Speech entering the left ear travels first to the right side of the brain before crossing to the brain's language center on the left side by way of the corpus callosum, a pathway connecting the brain's right and left hemispheres. NIDCD researchers based this finding from studies of identical and fraternal twins (national twins festival in Twinsburg, OH, during the years 2002 through 2005). 194 same-sex pairs of twins participated in the study (138 identical pairs and 56 fraternal pairs), representing ages 12 through 50. Researchers found a significantly higher correlation among identical twins than fraternal twins, indicating that differences in performance for those activities had a strong genetic component. It was found that if a trait is purely genetic, identical twins, who share the same DNA, will be alike nearly 100 percent of the time, while fraternal twins, who share roughly half of their DNA, will be less similar. Conversely, if a trait is primarily due to a person's environment, both identical and fraternal twins should have roughly the same degree of similarity, since most twins grow up in the same household.
I also got this from the Howard Hughes medical institute's web site.
http://www.hhmi.org/cgi-bin/askascienti ... s_018.htmlquestion
Submitted by Adrian, a high school teacher in Pasadena, California.
My students ask me this question all the time and I am stumped. Are fingerprints the same for twins? That is, are they based on development, on the genetic code, or a combination of both? On a molecular level, would two twins have the same DNA fingerprint? (Basically, how genetically identical are they?)
answer
Provided by Max Heiman, HHMI predoctoral fellow at the University of California, San Francisco.
I have no doubt your students ask the "twins' fingerprints" question often—I've only received a couple dozen questions through the Ask a Scientist program, and you're already the second to ask about it! I always thought that identical twins did have the same fingerprints, but apparently this is not always true.
In humans (and in most animals), it is hard to predict how the body will take shape during development. Some things are programmed in the DNA, but most seem to happen by chance within the bounds of certain rules. Identifying those rules is a big challenge in developmental biology right now.
In fruit flies, for instance, breathing tubes extend from every cell to the surface of the organism to supply it with oxygen. The complicated branching pattern of these tubes is different in every fly, even ones with the same DNA. But developmental biologists are beginning to understand the rules behind this pattern formation: as cells need oxygen, they send out a signal that causes a tube to grow towards them. So even though every fly seems to have a different pattern, development of these breathing tube patterns is governed by programmed rules.
Fingerprints might be like this—partly genetically preprogrammed and partly made up during development.
As you know, there are different kinds of twins: identical and fraternal. Identical twins come from a single zygote—that is, the fusion of a single sperm cell with a single egg cell. Their DNA is as closely related as the DNA of your hand is to that of your foot—in other words, identical. (However, there are some very interesting exceptions. For example, the immune systems of identical twins might not respond the same way to a disease. Since immune cells rearrange their DNA semi-randomly, the twins would make different sets of antibodies.) But for the most part identical twins' DNA would be identical in sequence, and since the DNA fingerprint is a rough representation of sequence, their DNA fingerprints also would be identical.
Fraternal twins are as related as any pair of siblings. Therefore, their DNA is 50 percent identical. Their DNA fingerprints would also be 50 percent identical (as are the DNA fingerprints of any siblings, or of a parent and child).
I did find one article that I wanted to tell you about: "Comparative diagnoses of twin zygosity by SSLP variant analysis, questionnaire, and dermatoglyphic analysis." Behavior Genetics 1996;6(1):55-63. The authors are Elisabeth Spitz, Rene Moutier, Terry Reed, Marie Claire Busnel, Catherine Marchaland, Pierre L. Roubertoux, and Michele Carlier. Here is my understanding of their work based on reading the paper's abstract.
The authors of that article used three methods to try to determine whether twins are monozygotic (identical), meaning they have the same DNA, or dizygotic (fraternal), meaning they share as much DNA as brothers and sisters do. The three methods were DNA analysis (DNA "fingerprinting"); fingerprint analysis (actual fingerprinting), and having the parents of the twins fill out a questionnaire on how similar the twins are. The authors thought that DNA analysis would enable them to tell every time whether the twins were identical or fraternal. But this approach is still fairly expensive. They found that the questionnaire could correctly identify 97% of the twins as identical or fraternal. Surprisingly, old-fashioned fingerprinting (what they call "dermatoglyphic analysis") was correct only 86% of the time.
You also might like to read about a roundworm called Caenorhabditis elegans. Unlike human cells, C. elegans cells always develop exactly the same way. We know exactly where each cell comes from, starting with the one-cell embryo and ending with the adult worm that has about 1,000 cells in its body. These cells always do everything exactly the same way. For this reason, C. elegans has been a great system for learning about genes that control development.
And this from the USA today website...
http://www.usatoday.com/tech/science/ge ... wins_x.htmA private lab in Dallas is set to try something never before attempted by scientists who investigate crimes: separate the DNA of identical twins to try to show which member of the pair committed a crime.
Unlike other people, twins begin life with the same genetic profile because they are formed when a single fertilized egg divides. But tiny mutations are known to occur in DNA, the cellular acid that carries the genetic code, as cells divide during an embryo's growth.
The lab, Orchid Cellmark, hopes to identify those differences to distinguish between the DNA of a pair of twins from Grand Rapids, Mich. The DNA of both men matches a semen sample from a November 1999 rape that was committed by one man.
The experiment is being watched closely by authorities across the nation. They say that in several cases, genetic evidence left at crime scenes — typically blood or semen — has linked identical twins to crimes that only one could have committed. The DNA testing used by law enforcement authorities and the FBI's national DNA database of convicted felons does not detect differences between identical twins.
Police in Virginia, Massachusetts and Texas have had a half-dozen such cases during the past two years, authorities say. Police in the United Kingdom have had several more.
Searching for tiny mutations in DNA is "a lot like looking for a needle in a haystack," says Robert Giles, Orchid Cellmark's director of U.S. operations. But "it also holds the possibility of doing something very useful."
So in lamemans terms Identical twins do have Identical DNA at birth but little mutations caused by viruses and pathegens over the years can alter the DNA an a sub-celular level and at this time we can barly track these differences.
[ Click to attempt signal recovery... ]
