Normally, there is only one egg available in the womb at any given time ready for fertilization. If there are two or more eggs present and they are fertilized, the result is fraternal twins (or triplets, etc.). Because the eggs are fertilized by different sperm, each resulting child's DNA will be different, and thus their genetic blueprints will be different. They may look very different physically, sound different, act different and have different health issues. Fraternal siblings may even be different genders. Fraternal twins will likely share some similar characteristics, however, as they have both inherited DNA from the same parents. The likelihood of having fraternal twins is determined entirely through the mother and factors affecting her reproductive system. A twin zygosity test can determine whether siblings are identical or fraternal twins.