Twins are two offspring produced by the same pregnancy. In contrast, a fetus that develops alone in the womb is called a singleton , and the general term for one offspring of a multiple birth is multiple. The Yoruba peoples have the highest rate of twinning in the world, at 45—50 twin sets or 90— twins per 1, live births,    possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may stimulate the ovaries to release an egg from each side. In Central Africa , there are 18—30 twin sets or 36—60 twins per 1, live births. North America and Europe have intermediate rates of 9 to 16 twin sets per 1, live births.
Fraternal Twins: Facts, Information and Common Questions
Ask Marilyn: What Are the Chances of Boy-Girl Twins?
Every parent of twins faces the question "Are your twins identical or fraternal? Many think that being identical twins refers to how twins look and not how they form. Take a look at the biology that determines the sex combinations that are possible with identical and fraternal twins. The terms identical and fraternal don't describe what the twins look like, but actually how they form. Identical monozygotic twins are always of the same sex because they form from a single zygote fertilized egg that contains either male XY or female XX sex chromosomes. Fraternal twins can be either two girls, two boys, or one of each. These are the possible sex combinations:.
Whether your baby is a boy or a girl is determined by the chromosome it inherits from its father. The egg from its mother always contains an X female chromosome, but the sperm contains either a female or a Y male chromosome. When the egg is fertilized the chromosomes come together and if they are XY a baby boy is conceived and if they are XX a baby girl is conceived. In the s Dr Shettles found that female and male sperm had different characteristics.
Zyler, wearing rainbow leggings, scrutinized a pair of hot-pink-and-purple sneakers. Kadyn, in a T-Rex shirt, fixated on a musical cube that flashed colorful lights. Is Zyler a boy or a girl? How about Kadyn?