Non-disjunction

Non-disjunction Non-disjunction means that chromosomes fail to separate correctly when gametes are formed. Because of this, a sperm or egg cell may have two copies of a chromosomes or no copies of a chromosome.

Disorders caused by non-disjunction Down syndrome Patau syndrome Edward Syndrome Turner Syndrome Klinefelter Syndrome

Down Syndrome Trisomy 21 – 3 copies of chromsome 21 Causes cognitive impairment, facial abnormalities, heart defects and stomach problems

Patau Syndrome Trisomy 13 – 3 copies of chromsome 13 Causes major heart and brain damage along with deformities of the hands and feet. 90% of affected individuals die within a year after birth.

Edward Syndrome Trisomy 18 – 3 copies of chromosome 18 Causes major heart, kidney and brain deformities 50% die before 2 months of age. 90% die before 12 months of age.

Turner Syndrome Monosomy X – female with one X chromosome Normal life expectancy Can cause mild kidney problem, short height, webbed neck and sterility.

Klinefelter Syndrome Males with XXY genotype 1 out of 500 males have the condition but show no symptoms Creates reduced fertility