What causes a mixed race couple with twins to have one baby look white and the other black?

They always show it every couple years when it happens what is the cause of it. You got one black parent and one white parent or both parents are mixed themselves and one of there twins looks white and the other looks black; what causes that.What causes a mixed race couple with twins to have one baby look white and the other black?
The evolution of the different skin tones is thought to have occurred as follows: the haired primate ancestors of humans, like modern great apes, had light skin under their hair. When Hominids evolved relative hairlessness (the most likely function of which was to facilitate perspiration) , they evolved dark skin, needed to prevent low folate levels since they lived in sun-rich Africa. (The skin cancer connection is probably of secondary importance, since skin cancer usually kills only after the reproductive age and therefore does not exert much evolutionary selection pressure.) When humans migrated to less sun-intensive regions in the north, low vitamin D3 levels became a problem and light skin color re-emerged. (sexual selection and diet may well have played a part in the evolution of skin tone diversity, as well)





The Inuit and Yupik are special cases: even though they live in an extremely sun-poor environment, they have retained their relatively dark skin. This can be explained by the fact that their traditional fish-based diet provides plenty of vitamin D.





Human skin color can range from almost black (due to very high concentrations of the dark brown pigment melanin) to nearly colorless (appearing reddish white due to the blood in the skin) in different people. Skin color is determined by the amount and type of melanin, the pigment in the skin. Variation in skin color is largely due to genetic rather than environmental causes. As a general pattern people with ancestors from tropical regions (hence greater sunlight exposure) have darker skin than people with ancestors from subtropical regions. This is far from a hard and fast rule however, because many light skinned groups have managed to survive at the equator by way of social adaptation. The same can be said of dark skinned groups living at subtropical latitudes.


Melanin comes in two types: pheomelanin (red) and eumelanin (very dark brown). Both amount and type are determined by four to six genes which operate under incomplete dominance. One copy of each of those genes is inherited from each parent. Each gene comes in several alleles, resulting in a great variety of different skin tones.


So it's not solely a recessive dominant inheritance thing, like blood type. Fraternal twins can share 25% to 50% of their genes in common (depending on whether or not they were from a single divided egg or two separate eggs at the time of fertilization) Identical twins share 100% of their genes in common.


So with fraternal twins, it's perfectly possible for one to appear to be fairer skinned compared to the other. And their have been people with 100% African ancestry who have 'passed' for caucasians as well.What causes a mixed race couple with twins to have one baby look white and the other black?
This happens in intra-racial couples where one parent is white and the other is a heterozygous black person (has one copy of dominant black gene and a copy of recessive white gene). When such couple has a kid, there is always a 50/50 chance that the kid might be black or white.


Fraternal twins (non-identical) are born when 2 sperms fertilize 2 eggs. In this case each kid has his/her own set of chromosomes therefore, there are 50/50 chance that each kid might be black or white.
your i can't remeber what its called but in bio class. there is a chart and mens chromosomes are XYz and womens are XY so because both parents are mixed one of the chromosomes like XY and then the resesive gene z wasn't dominate so one of the twins is lighter because gene z wasn't dominate to the XY of the mother. and the other child was dominate to the whole gene XYZ so the 2nd twin would be darker because they have all dominate genes. If that makes sense/.
When twins are fraternal twins instead of identical twins, each baby has its own separate DNA, which determines skin color. Each set of DNA is like a roll of the dice between what will be inherited from each of the parents. One baby's dice turned up white; the other turned up black.
DNA. Mixed race people have white genes and black genes. So generally, one baby will look white and one baby will look black.