A multiple birth is when two or more babies are born from the same pregnancy. The most common types of multiple births are twins. There are two types of twins: identical and fraternal. Identical twins are caused by one egg being fertilized by one sperm. Sometimes after fertilization, the egg splits into two genetically identical halves. They have duplicate chromosomes, which leads to identical physical characteristics, such as hair color, eye color, and blood type. This type of twin accounts for about one in two hundred fifty births (Agnew, Klein & Robert, 17). Identical twins are always the same sex, although there has been about four very rare cases of opposite sex identical twins due to genetic abnormality (Agnew, Klein & Robert, 19). Identical twins share 100% of their genes, and are in reality, natural clones.
The second types of twins are fraternal twins. Fraternal twins are formed when two eggs released by the mother, and a different sperm fertilizes each egg (Twins). Fraternal twins are twice as common as identical twins. This type of twins can either be the same sex or opposite sex. They share up to
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