|MadSci Network: Genetics|
Victoria- Congratulations on having twin brothers in your family. You must be very proud and excited. In answer to your question - hair whorls between identical twins are not necessarily identical. In fact - they can grow in opposite directions altogether! Identical twins have, in the past, been considered by most to be carbon copies of one and other. However, scientists in the last few years have modified their definitions of the "identical" part of identical twins. It has been found that though identical twins are for all appearances exactly alike they still have differences in such characteristics as fingerprints, hair whorls, moles, and other visible traits. Some identical twins known as "mirror image twins" even have their internal organs arranged opposite one and other. As you probably know - identical, or "monozygotic," twins actually are formed from the same zygote in their mother. A zygote is the mother's egg that has been joined by the father's sperm. A zygote is the very first stage of a growing baby. Usually the cells of a zygote just keep on dividing but the zygote stays a single mass of cells. Sometimes the zygote separates into two masses of cells that develop into two babies. These two babies are referred to as identical twins and should have identical genes. So how do they get slight differences in appearance if they have the same genes - right? Well, it gets a little complicated here. There is a debate in the scientific community called "nature versus nurture". Basically, it is a debate over how much does the environment and our genetic composition affect who we are and how we look and act. Twins may have started out as the same zygote - but once divided they are subjected to different environmental conditions at different times (even in the womb). Scientists now believe that such environmental conditions as how much blood supply, oxygen, and nutrition a baby receives in the womb (as well as polarity) can play a part in how a twin developed. This may be the cause of such visible variations as differing hair whorls. Also, even though twins may have exactly the same number and composition of genes - the genes probably aren't all turned on at the same time or producing exact amounts of product in both twins - as these things can be influenced by environment. So one twin may have a gene that is producing a product that is not present in the other at that time - or possibly producing much more product than the other twin is producing. Though twins theoretically have "identical" DNA - if a scientist were to examine every molecule between them they would find tiny differences (called mutations). We're talking VERY slight differences here between identical twins - but technically differences just the same. This may not seem like a big deal to say that a set of identical twins are something like 99.9999% genetically similar, but let's consider that chimpanzees and humans are thought to be (at current estimate) 99% genetically similar in coding and non-coding regions to each other! We certainly don't look or act very much like chimpanzees even though we're 99% similar genetically. So it is that very small changes in genetic code can have a huge outcome on what an organism is like and how it acts - the extent of which we just aren't sure of yet. One thing is apparent concerning genetic research at this point - the pathways and mechanisms are extremely complex and scientists are just beginning to scratch the surface of what is yet to be known. Hopefully, in the not too distant future, we will have a better understanding of how these things work, Victoria. Thanks for the question and take care. Regards, Todd
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