FUNDC1 is a 155 amino acid protein belonging to the FUN14 family. The gene encoding FUNDC1 maps to human chromosome Xp11.3 and mouse chromosome X A1.2. The X and Y chromosomes are the human sex chromosomes. Chromosome X consists of about 153 million base pairs and nearly 1,000 genes. The combination of an X and Y chromosome lead to normal male development while two copies of X lead to normal female development. More than one copy of the X chromosome with a Y chromosome causes Klinefelter's syndrome.