Abnormal meiosis

Nondisjunction happens when two homologus chromosomes don’t separate during meiosis One pole ends up with an extra chromosome and one pole ends up missing a chromosome The abnormal separation of the tetrads causes resulting gametes to have one too many or one too few chromosomes

MonosomyTrisomy The resulting gamete in humans has only 22 chromosomes After fertilization, the individual will have only 45 chromosomes instead of 46. The resulting gamete has an extra chromosome – so 24. After fertilization, the individual will have 47 chromosomes.

TrisomyMonosomy

Abnormal foot and palm crease Also known as trisomy 21 – extra #21 chromosome is the most common cause Increases with the age of the mother Enlarged tongue, weak muscle tone Slanted eyes Occurs in 1/600 births (under 35 – 1/1000 – over 45 1/60)

Turner’s Syndrome – also called Monosomy X - XO  Female, sterile, don’t mature sexually, short stature, thick,wide neck,  About 1 in every 300o babies are born with Turner’s  Most Turner’s fetuses are miscarried by week 20  Only develop secondary sexual characteristics if given HRT

Female with a tendency toward male traits May be sterile (can be fertile) May be mentally challenged but may also have normal intelligence

XXY Male Sterile, underdeveloped sexually Thin, high pitched voice May be mentally challenged

Occurs in about 1 in 1000 newborn boys 5-10 boys are born in the US every day with this disorder Ed’s story Why it is called the “criminal chromosome”.

Because the Y chromosome is shorter than the X chromosome, YO babies are miscarried and never born.

Edward’s Syndrome A story of ElliotElliot