Topics: Twin, Conjoined twins, Twins Pages: 8 (1624 words) Published: April 13, 2015

Everything Better Comes in Pairs

Biology 1010
Professor Harvey
April 30, 2014
It’s crazy to think about how not too long ago the mystery of a woman having two or more babies at once was completely a miracle, and now it’s just another part of the evolution and life cycle. The concept of twins has been around since the idea of genetics and biology has been discovered. As evolution has progressed we have seen a change in the gene pool and this has resulted in mutations and the perception of twins. As time has proceeded twins have become more common in society. Often people say that they would love to have twins or they would have loved to be a twin. As you can see presented in the graph above twins have been on the rise since 1990 and they are continuing to grow in population. There are many different types of twins in the world today. The ones that are most common to society are Identical, Fraternal, and Siamese twins. Although twins are conceived at the same time and are in utero together, not all are identically the same and there are many similarities and differences between them. Actually most common among twins is either extreme similarity or extreme dissimilarity.

The first type of twins is identical twins and this means that they are genetically identical. The DNA sequences of identical twins are almost exactly the same, and this is why they look alike. They only use one fertilized egg that then splits into two and these twins can only be the same sex (Meyers 2004). These children have the same genes but they do not necessarily have the same number of those genes. The most common attributes with these twins is that they share the same birthdate, blood type and physical appearance in some rare cases they can even have different birthdays, sometimes the next day or in other circumstances they can be weeks or months apart. Even though people tend to think of twins as being identical only 1 out of every 250 pregnancies are identical twins. Only one third of all twins are identical throughout the world. Due to the genetic similarity identical twins are considered nature’s own human clones (Meyers 2004). Approximately one quarter of identical twins are mirror images of each other, which in other words is saying the right side of one child matches the left side of the other twin. The little differences in the twin’s appearances most often come from their environments, and not their genes (Meyers 2004).

Fraternal twins are those that develop from separate fertilized eggs, therefore they are no similar than any other set of siblings (Meyers 2004). In fact they can easily be compared to any regular set of siblings sometimes even mistaken for ordinary brothers and sisters. Fraternal twins have 50% of the same genes and the only difference between them and other siblings is their birthdays. Some researchers say that once you have had fraternal twins you are 3 to 4 times more likely to have another set (DDC 2008). Unlike identical twins, fraternal twins can be hereditary and run in the family and passed from mothers to daughters. Identical twins simply occur by coincidence and have not been proven to run in families. Another difference between identical and fraternal twins is that fraternal twins don’t always have the same blood type whereas identical twins always do (DDC 2008). Too much of a surprise there are rare cases when fraternal twins have been born months even years apart, the main cause of this is when parents do in vitro and fertilized more than one egg then freeze them for later use. When a mother is having fraternal twins they can and most likely will be different genders. If a woman doesn’t want to be pregnant at the given moment, but is of an older age this is a good alternative. Having fraternal twins are genetically predisposed, not random. DNA tests have shown that in rare cases a women is carrying twins from separate fathers, the reason...

References: 1.Facts About Twins [Internet]. [UMMC]. University of Maryland Medical Center; 2014 [cited 2014 April 30].
2.Martin JA, Hamilton BE, Osterman MJK. Three decades of twin births in the United States, 1980–2009. NCHS data brief, no 80. Hyattsville, MD: National Center for Health Statistics. 2012.
3.Meyers, David G. 2004. Psychology: Tenth Edition in Modules. New York (NY); Worth Publishers. 135 p.
4.Paternity Testing: Twins With Different Fathers [Internet]. [DDC] DNA Diagnostics Center; 2008 [cited 2014 April 30].
5.What are conjoined Twin? [Internet]. [SCHRF]. Seattle Childrens Hospital Research Foundation; 2014 [cited 2014 April 30].
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