Presentation on theme: "Abnormal meiosis. Nondisjunction happens when two homologus chromosomes don’t separate during meiosis One pole ends up with an extra chromosome and one."— Presentation transcript:
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.
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