Difference between Fraternal and Identical twins; fraternal twins are twins that do not look alike. A boy and girl are always fraternal but same gender twins are not always fraternal. Identical twins are ALWAYS the same gender and they have the same features so they look alike. Unlike identical twins—who are genetically the same—fraternal twins are no more closely related in terms of DNA than regular siblings.
Identical twins are when one egg is fertilized and the egg divides into two, Fraternal twins is when two eggs get fertilized. Having identical twins is not genetic. On the other hand, fraternal twins can run in families. Fraternal twins are “dizygotic,” meaning that they developed from two different eggs fertilized by two different sperm cells, while identical twins are “monozygotic”, they developed from a single fertilized egg that split. The like hood for identical twins to be the same are 3 out of 1,000 as fraternal is 6 out of 20 per 1,00 deliveries.
Who determines the twins, Mom or Dad? However, for a given pregnancy, only the mother’s genetics matter. Fraternal twins happen when two eggs are simultaneously fertilized instead of just one. A father’s genes can’t make a woman release two eggs. Genetics can definitely play a role in having fraternal twins. For example, a woman that has a sibling that is a fraternal twin is 2.5 times more likely to have twins than average!
Researchers like Boomsma have some ideas, especially as fraternal twin births are on the rise in Western countries—for instance, the United States saw a 76% increase from 1980 to 2011. Having one copy of each SNP increased a mother’s chance of having fraternal twins by 29%, they report today in The American Journal of Human Genetics
Twin studies reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics and in content fields, from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, pedigree, etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.
Twins are a valuable source for observation because they allow the study of environmental influence and varying genetic makeup: "identical" or monozygotic (MZ) twins share nearly 100% of their genes, which means that most differences between the twins (such as height, susceptibility to boredom, intelligence, depression, etc.) are due to experiences that one twin has but not the other twin. "Fraternal" or dizygotic (DZ) twins share only about 50% of their genes, the same as any other sibling. Twins also share many aspects of their environment (e.g., uterine environment, parenting style, education, wealth, culture, community) because they are born into the same family. The presence of a given genetic trait in only one member of a pair of identical twins (called discordance) provides a powerful window into environmental effects.
Twins are also useful in showing the importance of the unique environment (specific to one twin or the other) when studying trait presentation. Changes in the unique environment can stem from an event or occurrence that has only affected one twin. This could range form a head injury or a birth defect that one twin has sustained while the other remains healthy.