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

Monosomy Trisomy

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.

Trisomy Monosomy

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)

Down’s Syndrome

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 Elliot