Well they are using a 1% chance that an egg or a sperm would contain all white or all black genes.... not a 25% chance... so yea, if you do that, you easily get to 1 million....
1%? 25%?
Uhh, if they're using those percentages they need to go back to grade school or junior high and retake that first biology class. A few math classes couldn't hurt either.
It's NOT physically possible for either of those percentages to show up, at least when you're considering normal reproduction.
You see, we each have two chromosomes. One from our father, and one from our mother. If you're female, you have one X from your mother, and your father's X chromosome. If you're male you have one of your mother's X chromosomes, and your father's Y chromosome.
A sperm cell (rare mutations aside) EITHER the father's X chromosome or his Y chromosome. An egg (once again, mutations aside) contains EITHER her mother's X or her father's X.
Your chromosomes do not engage in wild orgies with one another as you are being conceived. They don't usually swap genetic material with one another. So, the chromosome you inherit from your mother is the same one she inherited from one of her parents. Likewise on the father's side.
*hint* You can't be 3/4ths Irish and 1/4th Black. You're either 50/50 or 100%. You're only related to TWO of your grandparents (unless they were inbreeding, in which case you should be posting on DU instead of here). It's not PC, but then no one's ever accused the laws of nature of being overly concerned with political correctness.
POP QUIZ!
What is the race of the PATERNAL GRANDMOTHER?
You can derive the answer from looking at a photograph of the twins. You need no other information.
If you fail this quiz, I will expect a 5-page report on Mendelian Genetics (double-spaced; 10-point font; Times New Roman). I expect you to define: Chromosome; Heredity and Heritable Traits.