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Case #018
I have a niece and a nephew living in California, both aged 22, in the lovely city of
Santa Monica. They are fraternal twins, a phenomenon which occurs when two different
eggs are fertilized at the same time by two different sperm cells; no zygote division ever
happens. Zygote division results in identical twins- a good example is the lovely Barbi
girls. Anyway, when you have identical twins, they must be of the same sex, and they look
absolutely identical. But, fraternal twins are just like normal siblings (possible different sex,
possible different eye color, possible different hair color, etc.) except for their simultaneous
birth. Well, as David and Gina were growing up, they were almost exactly the same height, until they
both reached the age of 12. At this age, my nephew was eating much more than my
niece, taking in much more protein, calcium, and zinc. Guess who was taller at the age
of 12? No, not David. Gina was the taller of the two at the age of 12, by at least three
inches. Even though she ate less, puberty occurs much earlier in girls than in boys. David
had caught up by the age of 14, however, and now is a full six inches taller.
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Exercises
