Nondisjunction occurs when chromosome pairs fail to separate during meiosis. As a result, gametes form having either too many or too few chromosomes, explains Education Portal. Offspring who inherit such gametes may exhibit genetic disorders related to chromosome number, such as Turner syndrome and Down syndrome, notes MedicineNet.com.
In humans, males typically possess an X and a Y sex chromosome, while females have two copies of the X chromosome, notes the National Human Genome Research Institute. Turner syndrome occurs when a female possesses only one X chromosome or one full and one incomplete X chromosome. In some individuals with Turner syndrome, only some of their cells are missing a complete X chromosome, while the rest of the cells have two complete copies. This chromosomal syndrome commonly results in symptoms including shorter-than-average stature, non-functioning ovaries, infertility, recurrent ear infections in childhood, heightened risk for high blood pressure and a wide neck.
While Turner syndrome is characterized by a missing chromosome or part of a chromosome, Down syndrome, also known as trisomy 21, occurs most often when an individual possesses an extra copy of chromosome 21, explains the National Down Syndrome Society. Complications of Down syndrome can include decreased cognitive functioning, growth retardation, hearing impairment and a protruding tongue that appears too large to fit inside of the mouth, explains MedicineNet.com.