Vocal-cord physiology, the shape of the oral cavity, the height and shape of the soft palate all influence the voice and result in different sounds produced. This and future studies will help determine how much control a person has. An earlier study Crawford conducted found that identical twins had genetic similarities related to voice characteristics. More fraternal twins are needed for better comparisons. Identical twins are genetically the same, Crawford said.
Fraternal twins share half the same genes.
All twins share the same environment for nine months. Crawford said he has noticed that fraternal twins don't participate in twins studies as often as identical twins. Fraternal twins don't tend to view themselves as unique. Puppala asks twins to read a short passage and pronounce selected vowel sounds. She also takes several facial measurements of each participant.