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The human twin birth rate in the United States rose 76% from 1980 through 2009, from 9.4 to 16.7 twin sets (18.8 to 33.3 twins) per 1,000 births. [5] The Yoruba people have the highest rate of twinning in the world, at 45–50 twin sets (90–100 twins) per 1,000 live births, [6] [7] [8] possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may ...
Dizygotic (fraternal) twins can be caused by a hyperovulation gene in the mother. [8] Although the father's genes do not influence the woman's chances of having twins, he could influence his children's chances of having twins by passing on a copy of the hyperovulation gene to them. Monozygotic (identical) twins do not run in families.
In 2019, a Chinese woman was reported to have two babies from different fathers, one of whom was her husband and the other was a man having a secret affair with her during the same time. [ 12 ] In 2022, a 19-year-old Brazilian from Mineiros gave birth to twins from two different fathers with whom she had sex on the same day.
In this system, the sex of an individual usually is determined by a pair of sex chromosomes. Typically, females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males typically have two different kinds of sex chromosomes (XY), and are called the heterogametic sex. [1]
Both twins born vaginally – this can occur both presented head first or where one comes head first and the other is breech and/or helped by a forceps/ventouse delivery; One twin born vaginally and the other by caesarean section. If the twins are joined at any part of the body – called conjoined twins, delivery is mostly by caesarean section.
Identical twin studies are a useful mechanism for assessing the role of genes and environment. Twin studies have also found that among twins with differing sexual orientations, homosexual twins were significantly more gender nonconforming than their heterosexual co-twin, and that this was noticeable from a young age. [29] Bailey states:
While HCG levels can vary throughout a pregnancy, they can be anywhere between 200 to 7,000 for a women carrying twins after the first five weeks since the last menstrual cycle, according to ...
A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. [1] Most organisms that create their offspring using sexual reproduction have two common sexes and a few less common intersex variations.