Biracial twins are either born of parents of two races, or as a result of what scientists call “heteropaternal superfecundation.”
Heteropaternal superfecundation is said to be common among stray dogs or cats which, if it mates with different breeds of dogs or cats, can have litters in which every puppy has a different sire (father).
Clinical Professor of Obstetrics and Gynaecology at Columbia University, Dr. Hilda Hutcherson, says it is possible for a woman who has had sex with men of two different races to conceive such pair of babies.
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In one scientific study on humans, the frequency of such incidents was 2.4 per cent among dizygotic twins whose parents had been involved in paternity suits.
One of such rare occurrences was that of a 19-year-old Texas woman who gave birth to twins of different fathers in 2008.
How it happens: Every month, a woman’s ovary releases one egg that can be fertilised by one sperm. But in the case of the Texan woman, she released two eggs.
And since sperm can remain alive and well and viable for up to five days in the reproductive tract, if a woman has sex with different men within those five days, the sperm from two men can fertilise the two different eggs.
For the Texas woman, sperm from the men of two different races she had sex with ended up fertilising her two eggs during the separate sexual encounters.
The result was a set of biracial twins, both of whom were male.
In the case of the Illinois twins, however, their parents are of mixed race — a Black father and a White mother.
Dean, Meyer, the twins and their White brother. Photo: Yahoo.
As reported in many foreign media, one of the twins, Kalani, inherited her mother Whitney Meyer’s lighter complexion, while twin sister Jarani got her darker complexion from her father, Tomas Dean.
They were born in April 2016.
Scientists say that a biracial couple expecting twins have approximately one in 500 chance of their twins being born with different skin colours.
According to Wikipedia, mixed twins are fraternal twins born to multiracial families that differ in skin colour and other traits considered to be racial features.
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The online resource site explains that in humans, a relatively small number of genes are thought to be responsible for human skin colour.
Gene variants, otherwise called “alleles,” are responsible for the differences in the level of melanin found in human skin. Melanin is a dark brown or black substance that is a natural part of people’s skin, hair and eyes.
In some groups, there are high frequencies of dark skin alleles, while others have high frequencies of light skin alleles. The parents of biracial twins, who are typically both of mixed race, have a combination of alleles for light and dark skin in their genome.
In terms of fertilisation of the eggs during sex, researchers say each sperm (from the father) or egg cell (from the mother) possesses a random selection of genes from either parent.
Even though it rarely happens, a sperm or egg may randomly acquire, for example, mostly alleles that confer light skin coloration or mostly alleles that confer dark skin coloration. When this happens, fraternal twins can differ from each other quite dramatically in terms of skin colour or other physical characteristics.
Fraternal twins are twins that developed from separate fertilised eggs, they are genetically distinct and may not necessarily be of the same sex.
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