Huntington's disease, which causes degeneration of neurons, runs in Mark's family. Huntington's is a heritable, autosomal dominant genetic disease. In an autosomal dominant disease, only one abnormal allele is required to cause the disease in offspring. However, it is possible that not all offspring will receive the abnormal allele from an affected heterozygous parent. Family members that have the disease include Mark's maternal grandfather and Mark's maternal aunts. Mark's maternal grandmother does not have the disease. Because symptoms of Huntington's disease do not appear until later in life, genetic testing is necessary to determine whether a younger individual possesses the allele for the disease. These tests determined that Mark's mother does not carry the allele for Huntington's disease. Mark's paternal aunt suggested that Mark create a pedigree to track the disease in his family. Use the symbols provided to complete the pedigree. Each symbol may be used more than once.