KARYOTYPING AND NON-DISJUNCTION

What is karyotyping? A method of identification of chromosomes Pictures of chromosomes are taken as the cell undergoes mitosis The image is enlarged Individual chromosomes are cut up Chromosomes are matched up based on:  Size (largest to smallest)  Centromere position  G-banding

A mess of chromosomes…

After karyotyping… a normal male

After karyotyping…normal

Non-disjunction nondisjunction nondisjunction Non-disjunction is a failure of chromosomes to properly separate during either Stage 1 or Stage 2 of meiosis Upon fertilization the zygote may have one too many chromosomes ( trisomy) or one too few chromosomes (monosomy) All but one monosomy case results in death

Non-disjunction Non-disjunction occurs quite often among humans Impact is so severe to the zygote that miscarriage occurs very early in the pregnancy If the baby survives, it develops a set of traits that we call a syndrome

Down’s Syndrome Most commonly known trisonomy 1:700 births; 1 in 6 die within 1 st year Average age is 16.2 years Common facial feature Short stature Stubby fingers and toes Large tongue – makes speech difficult

Down’s syndrome

Down’s Syndrome One of the most common causes of mental disability (IQ is in the range) Prone to heart defects, respiratory problems and leukemia

Down’s Syndrome Odds of having a Down’s child increases with the age of the mother 1 in 1500 if mom is in early 20’s 1 in 70 if mom is over 35 1 in 25 if mom is over 45

Patau Syndrome 1:15,000 births as most fetuses die before term Of those that survive, 5% live to age 3; 45% die within the first month Serious eye, brain, and circulatory defects

Patau’s Syndrome

Edward’s Syndrome Only 10% survive past one year All die early in infancy Many complications

These are the only known trisonomy genetic disorders that result in offspring surviving for a short period of time

Non-disjunction of the sex chromosomes These can be fatal Most do survive just fine

Klinefelter’s Syndrome Affects 1:500 males XXY Tall, sterile males Normal intelligence Has female characteristics

Klinefelter’s Syndrome

Jacob’s Syndrome (super male) XYY Somewhat taller than average Slightly below normal intelligence 1:1000 males Extra testosterone

XXX (super female?) 1:1000 live births Normal intelligence Fertile No physical problems There are some women who are XXXX and XXXXX – each increasing X results in lesser intelligence and fertility

Monosomy – Turner’s Syndrome (XO) 1:2700 births Live normal lives but do not mature sexually at puberty Sterile Short stature Short broad neck Broad chest

Other chromosomal issues Deletion – a segment of the chromosome is missing Example: Cri-du-chat (1:1,000,000)  Improperly developed larynx  Severely mentally handicapped

Other chromosomal issues Duplication Ex. Fragile X 1:1500 males, 2500 females Most common form of mentally handicapped offspring