Reproductive Systems Gametogenesis and Early Development
Which of the following statements is true regarding twin formation?
|A||Identical twins result from the fertilization of one egg by two sperm.|
|B||Fraternal twins result when two eggs are mistakenly released at once, and each is fertilized by one sperm.|
|C||Fraternal twins result when one egg is fertilized by one sperm, and the developing embryo splits apart, each part being able to grow into a new individual.|
|D||Identical twins are not really genetically identical.|
Identical twins result when one egg is fertilized by one sperm, as normal, but for some reason the two cells that result after the zygote divides become separated; at this early stage, each of the cells can go on to produce a complete individual. Fraternal twins are created when two eggs are mistakenly released, and are fertilized by separate sperm. Thus identical twins are in fact genetically identical, while fraternal twins are no more genetically related than any siblings. Of course, identical twins are not identical in all of their characteristics, due to the influence of the environment on development. Choice B is the only answer consistent with this information.