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-disjunctionnondisjunction 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 1st 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 25-75 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 X1:1500 males, 2500 femalesMost common form of mentally handicapped offspring