Medical Genetics Monosomy is lack of one of a pair of chromosomes, An individual having only one chromosome 6 is said to have monosomy 6. A common monosomy seen in many species is X chromosome monosomy, also known as Turner's syndrome. Monosomy is most commonly lethal during prenatal developmentMedical Genetics Monosomy is lack of one of a pair of chromosomes. An individual having only one chromosome 6 is said to have monosomy 6. A common monosomy seen in many species is X chromosome monosomy, also known as Turner's syndrome. Monosomy is most commonly lethal during prenatal development