Question

in genetics, a mother has two children who are twins. the children, one has a black skin while the other has a white skin, explain the genetics behind this? Note, the skin complexion of the children has nothing to do with the father.

Answer 1

Does it say the skin color of the mother? or does it specify whether twins are fraternal or monozygotic?

Answer 2

the skin colour of the mothe is dark too. they are identical twins

Answer 3

the skin colour is determined by more than one gene (hence there are mixed types, obviously). now if you have mixed blood type and your mother is white and the dad is black (and same goes for your partner), you can potentionally have kids this way. since most likely, the genes are codominant in their succession, odds are about one in a million that this happens and one is truly black and one truly white.

Answer 4

god doesn't throw dice? well, he does. :-)

Answer 5

ok, so I would say that since skin color is primarily a dominant trait (dark), then there would have to be some sort of point mutation or multiple mutation in the monozygotic twin in the gene or regulatory elements that later express the protein melanin.

The twin cannot have albinism, I would say because then the other twin would also be albino. See http://www.biology-online.org/3/1_genetic_control.htm, for more information on melanin and skin color expression

but due to the fact that they are identical and one twin expresses the dominant phenotype from mom, it must be a mutation.

Answer 6

nono, no mutation ^^ just basic luck. :-) see, this is what I found in the interwebz:

"If a woman is of mixed race, her eggs will usually contain a mixture of genes coding for both black and white skin.

Similarly, a man of mixed race will have a variety of different genes in his sperm. When these eggs and sperm come together, they will create a baby of mixed race.

But, very occasionally, the egg or sperm might contain genes coding for one skin colour. If both the egg and sperm contain all white genes, the baby will be white. And if both contain just the versions necessary for black skin, the baby will be black.

For a mixed-race couple, the odds of either of these scenarios is around 100 to one. But both scenarios can occur at the same time if the woman conceives non-identical twins, another 100 to one chance.

This involves two eggs being fertilised by two sperm at the same time, which also has odds of around 100 to one.

If a sperm containing all-white genes fuses with a similar egg and a sperm coding for purely black skin fuses with a similar egg, two babies of dramatically different colours will be born.

The odds of this happening are 100 x 100 x 100 - a million to one."

( http://www.dailymail.co.uk/news/article-377839/Black-white-twins.html#ixzz1gRC8ZFgl)

Answer 7

the identical twins(monozygotic) is whats throwing a wrench in the theory of inheritance... this is why I suspect that its either mutation or differences in gene regulation (switching of expression on or off), if they were fraternal or just siblings... it would make perfect sense

Answer 8

oops, overread "identical twins". well, yours is even more unlikely than mine, but makes sense, oddly enough ^^

Answer 9

I dont get why the skin complexion would have nothing to do with the father, though... and the mutation must've happened nearly instantly after the first cell division - since the skin stem cells obviously all wear it. in this phase of development, usually evolution protects you enough for that to not happen. but hell, chances are that I fall right through my chair in a moment and get quantum mechanically stuck :D

Answer 10

yes interesting question, i'd like to sequence these twins genome! ha